National Strategy for the Survival of Released Line Caught Fish: investigating survival of fish released in Australia’s tropical and subtropical line fisheries

Project number: 2003-019
Project Status:
Completed
Budget expenditure: $674,340.00
Principal Investigator: Ian Brown
Organisation: James Cook University (JCU)
Project start/end date: 29 Jun 2003 - 28 Feb 2008
Contact:
FRDC
TAGS
Wild Catch
Tagging
Survey
Recreational Fishing
Fishing Gear
SPECIES
Redthroat Emperor
Spangled Emperor
Saddletail Snapper
Crimson Snapper
Red Emperor

Need

The report by McLeay et al. (2002) (“National strategy for the survival of line-caught fish: a review of research and fishery information”) summarises the need for this research as follows:

“The commercial and recreational line fisheries are the most highly participatory of all Australia’s fisheries. They are managed by a complex array of regulations, including size and catch limits, which create a high potential for captured fish to be released. The growing interest of recreational and charter fishers in catch-and-release practices has also increased release rates of line-caught fish. The susceptibility of line-caught fish to post-release mortality (PRM) is largely unknown, and is not taken into account in most current stock assessments”.

Perhaps half of the fish caught by line in Australia are released, for a variety of reasons including minimum legal sizes, bag limits, catch-release philosophy etc. However, we have little idea of how many of these die as a result of hook damage, inappropriate handling, barotrauma or capture stress, nor what effect this source of ‘cryptic’ mortality will have on the long-term sustainability of the various fisheries.

While there is good information on release rates in the recreational line fishing sector there is also a need to test the supposition that the commercial sector catches few undersized fish and also establish any differences between the general recreational community and the charter sector.

To more realistically appreciate the full effect of line fishing on the various species, the released catch needs to be described and quantified, and an attempt made to estimate post-release survival (PRS) rates. Alternative capture methods (hook designs) need to be tested, to determine whether a change in apparatus (via regulation or a Code of Practice) could reduce the catch of undersized fish. Pre-release handling and barotrauma relief procedures need to be evaluated to determine whether any changes may increase survival of fish returned to the water.

Objectives

1. To quantify the effects of hook type, hooking damage, barotrauma and barotrauma relief procedures on the short-term post-release survival (PRS) of key tropical and sub-tropical line-caught fish species.
2. To quantify the effects of hook type, hooking damage, barotrauma and barotrauma relief procedures on the long-term post-release survival (PRS) of key tropical and sub-tropical line-caught fish species.
3. To develop and extend ‘best practice’ handling procedures applicable to the recreational, commercial and charterboat sectors in Queensland, the Northern Territory and Western Australia.

Final report

ISBN: 978 0 7345 0393 0
Author: Ian Brown
Final Report • 2011-11-24
2003-019-DLD.pdf

Summary

Experiments were conducted in northern, central and southern Queensland to investigate the effects of hook design and size on the incidence of hooking injury, and the effects of a number of factors, including barotrauma-treatment method, on post-release survival rates of a suite of key reef-associated demersal fish species of particular importance to Queensland’s reef line fishery. The key species examined were common coral trout (Plectropomus leopardus), redthroat emperor (Lethrinus miniatus), crimson snapper (Lutjanus erythropterus), saddletail snapper (Lutjanus malabaricus), red emperor (Lutjanus sebae) and spangled emperor (Lethrinus nebulosus).

The work comprised four components:
(i) Analysis of existing datasets in terms of discarding/release rates in the commercial, recreational and charter sectors and estimation of barotrauma treatment effects;
(ii) Field trials to determine experimentally the effects of three hook patterns (J-hooks, offset circles and non-offset circles) and two sizes (small: 4/0 or 5/0, and large: 8/0) on hooking injury, location of hook lodgment and catch rate;
(iii) Field experiments using specially-developed vertical floating enclosures to test short-term (3-day) survival rates of fish treated to relieve barotrauma by venting or shotline releasing;
(iv) A community-based tag-release-recapture experiment involving recreational anglers to test the effects of barotrauma treatment and other covariates on long-term (months to years) post-release survival.

Discarding rates of some species have increased since 1997 largely as a result of increases in legislated minimum legal size limits and the introduction of maximum size limits. In December 2003 the minimum legal size (MLS) limit for red emperor was raised significantly, from 45 cm (TL) to 55 cm. Concurrent increases in MLS of bluespot coral trout, redthroat emperor and spangled emperor did not result in an observable change in discard rate. By 2005 the reported recreational discarding rates for coral trout, redthroat emperor, spangled emperor and saddletail snapper ranged between 42% and 55%, but for crimson snapper the rate was 69%, and for red emperor it was 83%. Between 1989 and 2003 some 300–620 t of coral trout and 33–95 t of redthroat emperor were discarded annually by the commercial reef line fishery on the GBR. Modelling of potential high-grading after the introduction of a (competitive) total allowable commercial catch for coral trout indicated that discarding of this species could increase to as much as 3,900 t. Spatial (but not temporal) differences in discarding rates were significant, and modelling indicated a potential for large increases in discarding rates and subsequent cryptic mortality as a result of changes in management arrangements.

The effects of hook pattern varied between species, with no consistent significant trends. Across all species only a relatively small proportion of fish (< 4%) were deep-hooked (in the throat or gut). Small hooks (5/0 circle and 4/0 J-hooks) were more likely to lodge in the lip or mouth than large hooks, although the effect was weak. Crimson snapper were significantly less prone to damage from non-offset circle hooks than either of the other patterns, but the opposite trend occurred with saddletail snapper. There was also a weak tendency for coral trout to sustain more injuries when captured on J-hooks or offset circle hooks than on non-offset circles. Hook size showed a more consistent trend, with large (8/0) circle or J-hooks being more frequently associated with injury than small hooks in all species, but this was statistically significant only in coral trout and blackblotch emperor. 

Our controlled short-term (3-day) field experiments revealed that hook location was a major determinant of short-term survival in coral trout, crimson snapper and saddletail snapper. Even when the hooks were left in place according to best practice procedures, survival rates among deep-hooked fish were considerably reduced compared to those hooked in the mouth or lip. The modelled survival rates of shallow and deep-hooked fish repectively were as follows: coral trout 81 and 50%, redthroat emperor 86 and 59%, crimson snapper 96 and 35%, and saddletail snapper 73 and 38%. This represents an overall reduction across species in survival rate of around 50% as a result of deep hooking, even when the hooks were left in place. The results of our hooking damage experiment showed that the incidence of deep hooking was generally low across the species examined (< 4%), so that the predicted added mortality due to deep hooking would be in the order of 0.04 × 0.50, or 2%. However this figure probably underestimates the actual value, as not all anglers are prepared to cut their hooks off if the hooks have become lodged in the gullet or gut. It is also likely that the higher level of angling skill among researchers conducting the hooking trials accounted for a lower incidence of deep-hooking than might be expected across the general angling community. 

Keywords: Released fish, Hook design, hooking injury, barotrauma, post-release survival, demersal fish species, reef line fishery, Coral Trout (Plectropomus leopardus), Redthroat Emperor (Lethrinus miniatus), Crimson Snapper (Lutjanus erythropterus), Saddletail Snapper (Lutjanus malabaricus), Red Emperor (Lutjanus sebae) and Spangled Emperor (Lethrinus nebulosus)

Final Report • 2011-11-24
2003-019-DLD.pdf

Summary

Experiments were conducted in northern, central and southern Queensland to investigate the effects of hook design and size on the incidence of hooking injury, and the effects of a number of factors, including barotrauma-treatment method, on post-release survival rates of a suite of key reef-associated demersal fish species of particular importance to Queensland’s reef line fishery. The key species examined were common coral trout (Plectropomus leopardus), redthroat emperor (Lethrinus miniatus), crimson snapper (Lutjanus erythropterus), saddletail snapper (Lutjanus malabaricus), red emperor (Lutjanus sebae) and spangled emperor (Lethrinus nebulosus).

The work comprised four components:
(i) Analysis of existing datasets in terms of discarding/release rates in the commercial, recreational and charter sectors and estimation of barotrauma treatment effects;
(ii) Field trials to determine experimentally the effects of three hook patterns (J-hooks, offset circles and non-offset circles) and two sizes (small: 4/0 or 5/0, and large: 8/0) on hooking injury, location of hook lodgment and catch rate;
(iii) Field experiments using specially-developed vertical floating enclosures to test short-term (3-day) survival rates of fish treated to relieve barotrauma by venting or shotline releasing;
(iv) A community-based tag-release-recapture experiment involving recreational anglers to test the effects of barotrauma treatment and other covariates on long-term (months to years) post-release survival.

Discarding rates of some species have increased since 1997 largely as a result of increases in legislated minimum legal size limits and the introduction of maximum size limits. In December 2003 the minimum legal size (MLS) limit for red emperor was raised significantly, from 45 cm (TL) to 55 cm. Concurrent increases in MLS of bluespot coral trout, redthroat emperor and spangled emperor did not result in an observable change in discard rate. By 2005 the reported recreational discarding rates for coral trout, redthroat emperor, spangled emperor and saddletail snapper ranged between 42% and 55%, but for crimson snapper the rate was 69%, and for red emperor it was 83%. Between 1989 and 2003 some 300–620 t of coral trout and 33–95 t of redthroat emperor were discarded annually by the commercial reef line fishery on the GBR. Modelling of potential high-grading after the introduction of a (competitive) total allowable commercial catch for coral trout indicated that discarding of this species could increase to as much as 3,900 t. Spatial (but not temporal) differences in discarding rates were significant, and modelling indicated a potential for large increases in discarding rates and subsequent cryptic mortality as a result of changes in management arrangements.

The effects of hook pattern varied between species, with no consistent significant trends. Across all species only a relatively small proportion of fish (< 4%) were deep-hooked (in the throat or gut). Small hooks (5/0 circle and 4/0 J-hooks) were more likely to lodge in the lip or mouth than large hooks, although the effect was weak. Crimson snapper were significantly less prone to damage from non-offset circle hooks than either of the other patterns, but the opposite trend occurred with saddletail snapper. There was also a weak tendency for coral trout to sustain more injuries when captured on J-hooks or offset circle hooks than on non-offset circles. Hook size showed a more consistent trend, with large (8/0) circle or J-hooks being more frequently associated with injury than small hooks in all species, but this was statistically significant only in coral trout and blackblotch emperor. 

Our controlled short-term (3-day) field experiments revealed that hook location was a major determinant of short-term survival in coral trout, crimson snapper and saddletail snapper. Even when the hooks were left in place according to best practice procedures, survival rates among deep-hooked fish were considerably reduced compared to those hooked in the mouth or lip. The modelled survival rates of shallow and deep-hooked fish repectively were as follows: coral trout 81 and 50%, redthroat emperor 86 and 59%, crimson snapper 96 and 35%, and saddletail snapper 73 and 38%. This represents an overall reduction across species in survival rate of around 50% as a result of deep hooking, even when the hooks were left in place. The results of our hooking damage experiment showed that the incidence of deep hooking was generally low across the species examined (< 4%), so that the predicted added mortality due to deep hooking would be in the order of 0.04 × 0.50, or 2%. However this figure probably underestimates the actual value, as not all anglers are prepared to cut their hooks off if the hooks have become lodged in the gullet or gut. It is also likely that the higher level of angling skill among researchers conducting the hooking trials accounted for a lower incidence of deep-hooking than might be expected across the general angling community. 

Keywords: Released fish, Hook design, hooking injury, barotrauma, post-release survival, demersal fish species, reef line fishery, Coral Trout (Plectropomus leopardus), Redthroat Emperor (Lethrinus miniatus), Crimson Snapper (Lutjanus erythropterus), Saddletail Snapper (Lutjanus malabaricus), Red Emperor (Lutjanus sebae) and Spangled Emperor (Lethrinus nebulosus)

Final Report • 2011-11-24
2003-019-DLD.pdf

Summary

Experiments were conducted in northern, central and southern Queensland to investigate the effects of hook design and size on the incidence of hooking injury, and the effects of a number of factors, including barotrauma-treatment method, on post-release survival rates of a suite of key reef-associated demersal fish species of particular importance to Queensland’s reef line fishery. The key species examined were common coral trout (Plectropomus leopardus), redthroat emperor (Lethrinus miniatus), crimson snapper (Lutjanus erythropterus), saddletail snapper (Lutjanus malabaricus), red emperor (Lutjanus sebae) and spangled emperor (Lethrinus nebulosus).

The work comprised four components:
(i) Analysis of existing datasets in terms of discarding/release rates in the commercial, recreational and charter sectors and estimation of barotrauma treatment effects;
(ii) Field trials to determine experimentally the effects of three hook patterns (J-hooks, offset circles and non-offset circles) and two sizes (small: 4/0 or 5/0, and large: 8/0) on hooking injury, location of hook lodgment and catch rate;
(iii) Field experiments using specially-developed vertical floating enclosures to test short-term (3-day) survival rates of fish treated to relieve barotrauma by venting or shotline releasing;
(iv) A community-based tag-release-recapture experiment involving recreational anglers to test the effects of barotrauma treatment and other covariates on long-term (months to years) post-release survival.

Discarding rates of some species have increased since 1997 largely as a result of increases in legislated minimum legal size limits and the introduction of maximum size limits. In December 2003 the minimum legal size (MLS) limit for red emperor was raised significantly, from 45 cm (TL) to 55 cm. Concurrent increases in MLS of bluespot coral trout, redthroat emperor and spangled emperor did not result in an observable change in discard rate. By 2005 the reported recreational discarding rates for coral trout, redthroat emperor, spangled emperor and saddletail snapper ranged between 42% and 55%, but for crimson snapper the rate was 69%, and for red emperor it was 83%. Between 1989 and 2003 some 300–620 t of coral trout and 33–95 t of redthroat emperor were discarded annually by the commercial reef line fishery on the GBR. Modelling of potential high-grading after the introduction of a (competitive) total allowable commercial catch for coral trout indicated that discarding of this species could increase to as much as 3,900 t. Spatial (but not temporal) differences in discarding rates were significant, and modelling indicated a potential for large increases in discarding rates and subsequent cryptic mortality as a result of changes in management arrangements.

The effects of hook pattern varied between species, with no consistent significant trends. Across all species only a relatively small proportion of fish (< 4%) were deep-hooked (in the throat or gut). Small hooks (5/0 circle and 4/0 J-hooks) were more likely to lodge in the lip or mouth than large hooks, although the effect was weak. Crimson snapper were significantly less prone to damage from non-offset circle hooks than either of the other patterns, but the opposite trend occurred with saddletail snapper. There was also a weak tendency for coral trout to sustain more injuries when captured on J-hooks or offset circle hooks than on non-offset circles. Hook size showed a more consistent trend, with large (8/0) circle or J-hooks being more frequently associated with injury than small hooks in all species, but this was statistically significant only in coral trout and blackblotch emperor. 

Our controlled short-term (3-day) field experiments revealed that hook location was a major determinant of short-term survival in coral trout, crimson snapper and saddletail snapper. Even when the hooks were left in place according to best practice procedures, survival rates among deep-hooked fish were considerably reduced compared to those hooked in the mouth or lip. The modelled survival rates of shallow and deep-hooked fish repectively were as follows: coral trout 81 and 50%, redthroat emperor 86 and 59%, crimson snapper 96 and 35%, and saddletail snapper 73 and 38%. This represents an overall reduction across species in survival rate of around 50% as a result of deep hooking, even when the hooks were left in place. The results of our hooking damage experiment showed that the incidence of deep hooking was generally low across the species examined (< 4%), so that the predicted added mortality due to deep hooking would be in the order of 0.04 × 0.50, or 2%. However this figure probably underestimates the actual value, as not all anglers are prepared to cut their hooks off if the hooks have become lodged in the gullet or gut. It is also likely that the higher level of angling skill among researchers conducting the hooking trials accounted for a lower incidence of deep-hooking than might be expected across the general angling community. 

Keywords: Released fish, Hook design, hooking injury, barotrauma, post-release survival, demersal fish species, reef line fishery, Coral Trout (Plectropomus leopardus), Redthroat Emperor (Lethrinus miniatus), Crimson Snapper (Lutjanus erythropterus), Saddletail Snapper (Lutjanus malabaricus), Red Emperor (Lutjanus sebae) and Spangled Emperor (Lethrinus nebulosus)

Final Report • 2011-11-24
2003-019-DLD.pdf

Summary

Experiments were conducted in northern, central and southern Queensland to investigate the effects of hook design and size on the incidence of hooking injury, and the effects of a number of factors, including barotrauma-treatment method, on post-release survival rates of a suite of key reef-associated demersal fish species of particular importance to Queensland’s reef line fishery. The key species examined were common coral trout (Plectropomus leopardus), redthroat emperor (Lethrinus miniatus), crimson snapper (Lutjanus erythropterus), saddletail snapper (Lutjanus malabaricus), red emperor (Lutjanus sebae) and spangled emperor (Lethrinus nebulosus).

The work comprised four components:
(i) Analysis of existing datasets in terms of discarding/release rates in the commercial, recreational and charter sectors and estimation of barotrauma treatment effects;
(ii) Field trials to determine experimentally the effects of three hook patterns (J-hooks, offset circles and non-offset circles) and two sizes (small: 4/0 or 5/0, and large: 8/0) on hooking injury, location of hook lodgment and catch rate;
(iii) Field experiments using specially-developed vertical floating enclosures to test short-term (3-day) survival rates of fish treated to relieve barotrauma by venting or shotline releasing;
(iv) A community-based tag-release-recapture experiment involving recreational anglers to test the effects of barotrauma treatment and other covariates on long-term (months to years) post-release survival.

Discarding rates of some species have increased since 1997 largely as a result of increases in legislated minimum legal size limits and the introduction of maximum size limits. In December 2003 the minimum legal size (MLS) limit for red emperor was raised significantly, from 45 cm (TL) to 55 cm. Concurrent increases in MLS of bluespot coral trout, redthroat emperor and spangled emperor did not result in an observable change in discard rate. By 2005 the reported recreational discarding rates for coral trout, redthroat emperor, spangled emperor and saddletail snapper ranged between 42% and 55%, but for crimson snapper the rate was 69%, and for red emperor it was 83%. Between 1989 and 2003 some 300–620 t of coral trout and 33–95 t of redthroat emperor were discarded annually by the commercial reef line fishery on the GBR. Modelling of potential high-grading after the introduction of a (competitive) total allowable commercial catch for coral trout indicated that discarding of this species could increase to as much as 3,900 t. Spatial (but not temporal) differences in discarding rates were significant, and modelling indicated a potential for large increases in discarding rates and subsequent cryptic mortality as a result of changes in management arrangements.

The effects of hook pattern varied between species, with no consistent significant trends. Across all species only a relatively small proportion of fish (< 4%) were deep-hooked (in the throat or gut). Small hooks (5/0 circle and 4/0 J-hooks) were more likely to lodge in the lip or mouth than large hooks, although the effect was weak. Crimson snapper were significantly less prone to damage from non-offset circle hooks than either of the other patterns, but the opposite trend occurred with saddletail snapper. There was also a weak tendency for coral trout to sustain more injuries when captured on J-hooks or offset circle hooks than on non-offset circles. Hook size showed a more consistent trend, with large (8/0) circle or J-hooks being more frequently associated with injury than small hooks in all species, but this was statistically significant only in coral trout and blackblotch emperor. 

Our controlled short-term (3-day) field experiments revealed that hook location was a major determinant of short-term survival in coral trout, crimson snapper and saddletail snapper. Even when the hooks were left in place according to best practice procedures, survival rates among deep-hooked fish were considerably reduced compared to those hooked in the mouth or lip. The modelled survival rates of shallow and deep-hooked fish repectively were as follows: coral trout 81 and 50%, redthroat emperor 86 and 59%, crimson snapper 96 and 35%, and saddletail snapper 73 and 38%. This represents an overall reduction across species in survival rate of around 50% as a result of deep hooking, even when the hooks were left in place. The results of our hooking damage experiment showed that the incidence of deep hooking was generally low across the species examined (< 4%), so that the predicted added mortality due to deep hooking would be in the order of 0.04 × 0.50, or 2%. However this figure probably underestimates the actual value, as not all anglers are prepared to cut their hooks off if the hooks have become lodged in the gullet or gut. It is also likely that the higher level of angling skill among researchers conducting the hooking trials accounted for a lower incidence of deep-hooking than might be expected across the general angling community. 

Keywords: Released fish, Hook design, hooking injury, barotrauma, post-release survival, demersal fish species, reef line fishery, Coral Trout (Plectropomus leopardus), Redthroat Emperor (Lethrinus miniatus), Crimson Snapper (Lutjanus erythropterus), Saddletail Snapper (Lutjanus malabaricus), Red Emperor (Lutjanus sebae) and Spangled Emperor (Lethrinus nebulosus)

Final Report • 2011-11-24
2003-019-DLD.pdf

Summary

Experiments were conducted in northern, central and southern Queensland to investigate the effects of hook design and size on the incidence of hooking injury, and the effects of a number of factors, including barotrauma-treatment method, on post-release survival rates of a suite of key reef-associated demersal fish species of particular importance to Queensland’s reef line fishery. The key species examined were common coral trout (Plectropomus leopardus), redthroat emperor (Lethrinus miniatus), crimson snapper (Lutjanus erythropterus), saddletail snapper (Lutjanus malabaricus), red emperor (Lutjanus sebae) and spangled emperor (Lethrinus nebulosus).

The work comprised four components:
(i) Analysis of existing datasets in terms of discarding/release rates in the commercial, recreational and charter sectors and estimation of barotrauma treatment effects;
(ii) Field trials to determine experimentally the effects of three hook patterns (J-hooks, offset circles and non-offset circles) and two sizes (small: 4/0 or 5/0, and large: 8/0) on hooking injury, location of hook lodgment and catch rate;
(iii) Field experiments using specially-developed vertical floating enclosures to test short-term (3-day) survival rates of fish treated to relieve barotrauma by venting or shotline releasing;
(iv) A community-based tag-release-recapture experiment involving recreational anglers to test the effects of barotrauma treatment and other covariates on long-term (months to years) post-release survival.

Discarding rates of some species have increased since 1997 largely as a result of increases in legislated minimum legal size limits and the introduction of maximum size limits. In December 2003 the minimum legal size (MLS) limit for red emperor was raised significantly, from 45 cm (TL) to 55 cm. Concurrent increases in MLS of bluespot coral trout, redthroat emperor and spangled emperor did not result in an observable change in discard rate. By 2005 the reported recreational discarding rates for coral trout, redthroat emperor, spangled emperor and saddletail snapper ranged between 42% and 55%, but for crimson snapper the rate was 69%, and for red emperor it was 83%. Between 1989 and 2003 some 300–620 t of coral trout and 33–95 t of redthroat emperor were discarded annually by the commercial reef line fishery on the GBR. Modelling of potential high-grading after the introduction of a (competitive) total allowable commercial catch for coral trout indicated that discarding of this species could increase to as much as 3,900 t. Spatial (but not temporal) differences in discarding rates were significant, and modelling indicated a potential for large increases in discarding rates and subsequent cryptic mortality as a result of changes in management arrangements.

The effects of hook pattern varied between species, with no consistent significant trends. Across all species only a relatively small proportion of fish (< 4%) were deep-hooked (in the throat or gut). Small hooks (5/0 circle and 4/0 J-hooks) were more likely to lodge in the lip or mouth than large hooks, although the effect was weak. Crimson snapper were significantly less prone to damage from non-offset circle hooks than either of the other patterns, but the opposite trend occurred with saddletail snapper. There was also a weak tendency for coral trout to sustain more injuries when captured on J-hooks or offset circle hooks than on non-offset circles. Hook size showed a more consistent trend, with large (8/0) circle or J-hooks being more frequently associated with injury than small hooks in all species, but this was statistically significant only in coral trout and blackblotch emperor. 

Our controlled short-term (3-day) field experiments revealed that hook location was a major determinant of short-term survival in coral trout, crimson snapper and saddletail snapper. Even when the hooks were left in place according to best practice procedures, survival rates among deep-hooked fish were considerably reduced compared to those hooked in the mouth or lip. The modelled survival rates of shallow and deep-hooked fish repectively were as follows: coral trout 81 and 50%, redthroat emperor 86 and 59%, crimson snapper 96 and 35%, and saddletail snapper 73 and 38%. This represents an overall reduction across species in survival rate of around 50% as a result of deep hooking, even when the hooks were left in place. The results of our hooking damage experiment showed that the incidence of deep hooking was generally low across the species examined (< 4%), so that the predicted added mortality due to deep hooking would be in the order of 0.04 × 0.50, or 2%. However this figure probably underestimates the actual value, as not all anglers are prepared to cut their hooks off if the hooks have become lodged in the gullet or gut. It is also likely that the higher level of angling skill among researchers conducting the hooking trials accounted for a lower incidence of deep-hooking than might be expected across the general angling community. 

Keywords: Released fish, Hook design, hooking injury, barotrauma, post-release survival, demersal fish species, reef line fishery, Coral Trout (Plectropomus leopardus), Redthroat Emperor (Lethrinus miniatus), Crimson Snapper (Lutjanus erythropterus), Saddletail Snapper (Lutjanus malabaricus), Red Emperor (Lutjanus sebae) and Spangled Emperor (Lethrinus nebulosus)

Final Report • 2011-11-24
2003-019-DLD.pdf

Summary

Experiments were conducted in northern, central and southern Queensland to investigate the effects of hook design and size on the incidence of hooking injury, and the effects of a number of factors, including barotrauma-treatment method, on post-release survival rates of a suite of key reef-associated demersal fish species of particular importance to Queensland’s reef line fishery. The key species examined were common coral trout (Plectropomus leopardus), redthroat emperor (Lethrinus miniatus), crimson snapper (Lutjanus erythropterus), saddletail snapper (Lutjanus malabaricus), red emperor (Lutjanus sebae) and spangled emperor (Lethrinus nebulosus).

The work comprised four components:
(i) Analysis of existing datasets in terms of discarding/release rates in the commercial, recreational and charter sectors and estimation of barotrauma treatment effects;
(ii) Field trials to determine experimentally the effects of three hook patterns (J-hooks, offset circles and non-offset circles) and two sizes (small: 4/0 or 5/0, and large: 8/0) on hooking injury, location of hook lodgment and catch rate;
(iii) Field experiments using specially-developed vertical floating enclosures to test short-term (3-day) survival rates of fish treated to relieve barotrauma by venting or shotline releasing;
(iv) A community-based tag-release-recapture experiment involving recreational anglers to test the effects of barotrauma treatment and other covariates on long-term (months to years) post-release survival.

Discarding rates of some species have increased since 1997 largely as a result of increases in legislated minimum legal size limits and the introduction of maximum size limits. In December 2003 the minimum legal size (MLS) limit for red emperor was raised significantly, from 45 cm (TL) to 55 cm. Concurrent increases in MLS of bluespot coral trout, redthroat emperor and spangled emperor did not result in an observable change in discard rate. By 2005 the reported recreational discarding rates for coral trout, redthroat emperor, spangled emperor and saddletail snapper ranged between 42% and 55%, but for crimson snapper the rate was 69%, and for red emperor it was 83%. Between 1989 and 2003 some 300–620 t of coral trout and 33–95 t of redthroat emperor were discarded annually by the commercial reef line fishery on the GBR. Modelling of potential high-grading after the introduction of a (competitive) total allowable commercial catch for coral trout indicated that discarding of this species could increase to as much as 3,900 t. Spatial (but not temporal) differences in discarding rates were significant, and modelling indicated a potential for large increases in discarding rates and subsequent cryptic mortality as a result of changes in management arrangements.

The effects of hook pattern varied between species, with no consistent significant trends. Across all species only a relatively small proportion of fish (< 4%) were deep-hooked (in the throat or gut). Small hooks (5/0 circle and 4/0 J-hooks) were more likely to lodge in the lip or mouth than large hooks, although the effect was weak. Crimson snapper were significantly less prone to damage from non-offset circle hooks than either of the other patterns, but the opposite trend occurred with saddletail snapper. There was also a weak tendency for coral trout to sustain more injuries when captured on J-hooks or offset circle hooks than on non-offset circles. Hook size showed a more consistent trend, with large (8/0) circle or J-hooks being more frequently associated with injury than small hooks in all species, but this was statistically significant only in coral trout and blackblotch emperor. 

Our controlled short-term (3-day) field experiments revealed that hook location was a major determinant of short-term survival in coral trout, crimson snapper and saddletail snapper. Even when the hooks were left in place according to best practice procedures, survival rates among deep-hooked fish were considerably reduced compared to those hooked in the mouth or lip. The modelled survival rates of shallow and deep-hooked fish repectively were as follows: coral trout 81 and 50%, redthroat emperor 86 and 59%, crimson snapper 96 and 35%, and saddletail snapper 73 and 38%. This represents an overall reduction across species in survival rate of around 50% as a result of deep hooking, even when the hooks were left in place. The results of our hooking damage experiment showed that the incidence of deep hooking was generally low across the species examined (< 4%), so that the predicted added mortality due to deep hooking would be in the order of 0.04 × 0.50, or 2%. However this figure probably underestimates the actual value, as not all anglers are prepared to cut their hooks off if the hooks have become lodged in the gullet or gut. It is also likely that the higher level of angling skill among researchers conducting the hooking trials accounted for a lower incidence of deep-hooking than might be expected across the general angling community. 

Keywords: Released fish, Hook design, hooking injury, barotrauma, post-release survival, demersal fish species, reef line fishery, Coral Trout (Plectropomus leopardus), Redthroat Emperor (Lethrinus miniatus), Crimson Snapper (Lutjanus erythropterus), Saddletail Snapper (Lutjanus malabaricus), Red Emperor (Lutjanus sebae) and Spangled Emperor (Lethrinus nebulosus)

Final Report • 2011-11-24
2003-019-DLD.pdf

Summary

Experiments were conducted in northern, central and southern Queensland to investigate the effects of hook design and size on the incidence of hooking injury, and the effects of a number of factors, including barotrauma-treatment method, on post-release survival rates of a suite of key reef-associated demersal fish species of particular importance to Queensland’s reef line fishery. The key species examined were common coral trout (Plectropomus leopardus), redthroat emperor (Lethrinus miniatus), crimson snapper (Lutjanus erythropterus), saddletail snapper (Lutjanus malabaricus), red emperor (Lutjanus sebae) and spangled emperor (Lethrinus nebulosus).

The work comprised four components:
(i) Analysis of existing datasets in terms of discarding/release rates in the commercial, recreational and charter sectors and estimation of barotrauma treatment effects;
(ii) Field trials to determine experimentally the effects of three hook patterns (J-hooks, offset circles and non-offset circles) and two sizes (small: 4/0 or 5/0, and large: 8/0) on hooking injury, location of hook lodgment and catch rate;
(iii) Field experiments using specially-developed vertical floating enclosures to test short-term (3-day) survival rates of fish treated to relieve barotrauma by venting or shotline releasing;
(iv) A community-based tag-release-recapture experiment involving recreational anglers to test the effects of barotrauma treatment and other covariates on long-term (months to years) post-release survival.

Discarding rates of some species have increased since 1997 largely as a result of increases in legislated minimum legal size limits and the introduction of maximum size limits. In December 2003 the minimum legal size (MLS) limit for red emperor was raised significantly, from 45 cm (TL) to 55 cm. Concurrent increases in MLS of bluespot coral trout, redthroat emperor and spangled emperor did not result in an observable change in discard rate. By 2005 the reported recreational discarding rates for coral trout, redthroat emperor, spangled emperor and saddletail snapper ranged between 42% and 55%, but for crimson snapper the rate was 69%, and for red emperor it was 83%. Between 1989 and 2003 some 300–620 t of coral trout and 33–95 t of redthroat emperor were discarded annually by the commercial reef line fishery on the GBR. Modelling of potential high-grading after the introduction of a (competitive) total allowable commercial catch for coral trout indicated that discarding of this species could increase to as much as 3,900 t. Spatial (but not temporal) differences in discarding rates were significant, and modelling indicated a potential for large increases in discarding rates and subsequent cryptic mortality as a result of changes in management arrangements.

The effects of hook pattern varied between species, with no consistent significant trends. Across all species only a relatively small proportion of fish (< 4%) were deep-hooked (in the throat or gut). Small hooks (5/0 circle and 4/0 J-hooks) were more likely to lodge in the lip or mouth than large hooks, although the effect was weak. Crimson snapper were significantly less prone to damage from non-offset circle hooks than either of the other patterns, but the opposite trend occurred with saddletail snapper. There was also a weak tendency for coral trout to sustain more injuries when captured on J-hooks or offset circle hooks than on non-offset circles. Hook size showed a more consistent trend, with large (8/0) circle or J-hooks being more frequently associated with injury than small hooks in all species, but this was statistically significant only in coral trout and blackblotch emperor. 

Our controlled short-term (3-day) field experiments revealed that hook location was a major determinant of short-term survival in coral trout, crimson snapper and saddletail snapper. Even when the hooks were left in place according to best practice procedures, survival rates among deep-hooked fish were considerably reduced compared to those hooked in the mouth or lip. The modelled survival rates of shallow and deep-hooked fish repectively were as follows: coral trout 81 and 50%, redthroat emperor 86 and 59%, crimson snapper 96 and 35%, and saddletail snapper 73 and 38%. This represents an overall reduction across species in survival rate of around 50% as a result of deep hooking, even when the hooks were left in place. The results of our hooking damage experiment showed that the incidence of deep hooking was generally low across the species examined (< 4%), so that the predicted added mortality due to deep hooking would be in the order of 0.04 × 0.50, or 2%. However this figure probably underestimates the actual value, as not all anglers are prepared to cut their hooks off if the hooks have become lodged in the gullet or gut. It is also likely that the higher level of angling skill among researchers conducting the hooking trials accounted for a lower incidence of deep-hooking than might be expected across the general angling community. 

Keywords: Released fish, Hook design, hooking injury, barotrauma, post-release survival, demersal fish species, reef line fishery, Coral Trout (Plectropomus leopardus), Redthroat Emperor (Lethrinus miniatus), Crimson Snapper (Lutjanus erythropterus), Saddletail Snapper (Lutjanus malabaricus), Red Emperor (Lutjanus sebae) and Spangled Emperor (Lethrinus nebulosus)

Final Report • 2011-11-24
2003-019-DLD.pdf

Summary

Experiments were conducted in northern, central and southern Queensland to investigate the effects of hook design and size on the incidence of hooking injury, and the effects of a number of factors, including barotrauma-treatment method, on post-release survival rates of a suite of key reef-associated demersal fish species of particular importance to Queensland’s reef line fishery. The key species examined were common coral trout (Plectropomus leopardus), redthroat emperor (Lethrinus miniatus), crimson snapper (Lutjanus erythropterus), saddletail snapper (Lutjanus malabaricus), red emperor (Lutjanus sebae) and spangled emperor (Lethrinus nebulosus).

The work comprised four components:
(i) Analysis of existing datasets in terms of discarding/release rates in the commercial, recreational and charter sectors and estimation of barotrauma treatment effects;
(ii) Field trials to determine experimentally the effects of three hook patterns (J-hooks, offset circles and non-offset circles) and two sizes (small: 4/0 or 5/0, and large: 8/0) on hooking injury, location of hook lodgment and catch rate;
(iii) Field experiments using specially-developed vertical floating enclosures to test short-term (3-day) survival rates of fish treated to relieve barotrauma by venting or shotline releasing;
(iv) A community-based tag-release-recapture experiment involving recreational anglers to test the effects of barotrauma treatment and other covariates on long-term (months to years) post-release survival.

Discarding rates of some species have increased since 1997 largely as a result of increases in legislated minimum legal size limits and the introduction of maximum size limits. In December 2003 the minimum legal size (MLS) limit for red emperor was raised significantly, from 45 cm (TL) to 55 cm. Concurrent increases in MLS of bluespot coral trout, redthroat emperor and spangled emperor did not result in an observable change in discard rate. By 2005 the reported recreational discarding rates for coral trout, redthroat emperor, spangled emperor and saddletail snapper ranged between 42% and 55%, but for crimson snapper the rate was 69%, and for red emperor it was 83%. Between 1989 and 2003 some 300–620 t of coral trout and 33–95 t of redthroat emperor were discarded annually by the commercial reef line fishery on the GBR. Modelling of potential high-grading after the introduction of a (competitive) total allowable commercial catch for coral trout indicated that discarding of this species could increase to as much as 3,900 t. Spatial (but not temporal) differences in discarding rates were significant, and modelling indicated a potential for large increases in discarding rates and subsequent cryptic mortality as a result of changes in management arrangements.

The effects of hook pattern varied between species, with no consistent significant trends. Across all species only a relatively small proportion of fish (< 4%) were deep-hooked (in the throat or gut). Small hooks (5/0 circle and 4/0 J-hooks) were more likely to lodge in the lip or mouth than large hooks, although the effect was weak. Crimson snapper were significantly less prone to damage from non-offset circle hooks than either of the other patterns, but the opposite trend occurred with saddletail snapper. There was also a weak tendency for coral trout to sustain more injuries when captured on J-hooks or offset circle hooks than on non-offset circles. Hook size showed a more consistent trend, with large (8/0) circle or J-hooks being more frequently associated with injury than small hooks in all species, but this was statistically significant only in coral trout and blackblotch emperor. 

Our controlled short-term (3-day) field experiments revealed that hook location was a major determinant of short-term survival in coral trout, crimson snapper and saddletail snapper. Even when the hooks were left in place according to best practice procedures, survival rates among deep-hooked fish were considerably reduced compared to those hooked in the mouth or lip. The modelled survival rates of shallow and deep-hooked fish repectively were as follows: coral trout 81 and 50%, redthroat emperor 86 and 59%, crimson snapper 96 and 35%, and saddletail snapper 73 and 38%. This represents an overall reduction across species in survival rate of around 50% as a result of deep hooking, even when the hooks were left in place. The results of our hooking damage experiment showed that the incidence of deep hooking was generally low across the species examined (< 4%), so that the predicted added mortality due to deep hooking would be in the order of 0.04 × 0.50, or 2%. However this figure probably underestimates the actual value, as not all anglers are prepared to cut their hooks off if the hooks have become lodged in the gullet or gut. It is also likely that the higher level of angling skill among researchers conducting the hooking trials accounted for a lower incidence of deep-hooking than might be expected across the general angling community. 

Keywords: Released fish, Hook design, hooking injury, barotrauma, post-release survival, demersal fish species, reef line fishery, Coral Trout (Plectropomus leopardus), Redthroat Emperor (Lethrinus miniatus), Crimson Snapper (Lutjanus erythropterus), Saddletail Snapper (Lutjanus malabaricus), Red Emperor (Lutjanus sebae) and Spangled Emperor (Lethrinus nebulosus)

Final Report • 2011-11-24
2003-019-DLD.pdf

Summary

Experiments were conducted in northern, central and southern Queensland to investigate the effects of hook design and size on the incidence of hooking injury, and the effects of a number of factors, including barotrauma-treatment method, on post-release survival rates of a suite of key reef-associated demersal fish species of particular importance to Queensland’s reef line fishery. The key species examined were common coral trout (Plectropomus leopardus), redthroat emperor (Lethrinus miniatus), crimson snapper (Lutjanus erythropterus), saddletail snapper (Lutjanus malabaricus), red emperor (Lutjanus sebae) and spangled emperor (Lethrinus nebulosus).

The work comprised four components:
(i) Analysis of existing datasets in terms of discarding/release rates in the commercial, recreational and charter sectors and estimation of barotrauma treatment effects;
(ii) Field trials to determine experimentally the effects of three hook patterns (J-hooks, offset circles and non-offset circles) and two sizes (small: 4/0 or 5/0, and large: 8/0) on hooking injury, location of hook lodgment and catch rate;
(iii) Field experiments using specially-developed vertical floating enclosures to test short-term (3-day) survival rates of fish treated to relieve barotrauma by venting or shotline releasing;
(iv) A community-based tag-release-recapture experiment involving recreational anglers to test the effects of barotrauma treatment and other covariates on long-term (months to years) post-release survival.

Discarding rates of some species have increased since 1997 largely as a result of increases in legislated minimum legal size limits and the introduction of maximum size limits. In December 2003 the minimum legal size (MLS) limit for red emperor was raised significantly, from 45 cm (TL) to 55 cm. Concurrent increases in MLS of bluespot coral trout, redthroat emperor and spangled emperor did not result in an observable change in discard rate. By 2005 the reported recreational discarding rates for coral trout, redthroat emperor, spangled emperor and saddletail snapper ranged between 42% and 55%, but for crimson snapper the rate was 69%, and for red emperor it was 83%. Between 1989 and 2003 some 300–620 t of coral trout and 33–95 t of redthroat emperor were discarded annually by the commercial reef line fishery on the GBR. Modelling of potential high-grading after the introduction of a (competitive) total allowable commercial catch for coral trout indicated that discarding of this species could increase to as much as 3,900 t. Spatial (but not temporal) differences in discarding rates were significant, and modelling indicated a potential for large increases in discarding rates and subsequent cryptic mortality as a result of changes in management arrangements.

The effects of hook pattern varied between species, with no consistent significant trends. Across all species only a relatively small proportion of fish (< 4%) were deep-hooked (in the throat or gut). Small hooks (5/0 circle and 4/0 J-hooks) were more likely to lodge in the lip or mouth than large hooks, although the effect was weak. Crimson snapper were significantly less prone to damage from non-offset circle hooks than either of the other patterns, but the opposite trend occurred with saddletail snapper. There was also a weak tendency for coral trout to sustain more injuries when captured on J-hooks or offset circle hooks than on non-offset circles. Hook size showed a more consistent trend, with large (8/0) circle or J-hooks being more frequently associated with injury than small hooks in all species, but this was statistically significant only in coral trout and blackblotch emperor. 

Our controlled short-term (3-day) field experiments revealed that hook location was a major determinant of short-term survival in coral trout, crimson snapper and saddletail snapper. Even when the hooks were left in place according to best practice procedures, survival rates among deep-hooked fish were considerably reduced compared to those hooked in the mouth or lip. The modelled survival rates of shallow and deep-hooked fish repectively were as follows: coral trout 81 and 50%, redthroat emperor 86 and 59%, crimson snapper 96 and 35%, and saddletail snapper 73 and 38%. This represents an overall reduction across species in survival rate of around 50% as a result of deep hooking, even when the hooks were left in place. The results of our hooking damage experiment showed that the incidence of deep hooking was generally low across the species examined (< 4%), so that the predicted added mortality due to deep hooking would be in the order of 0.04 × 0.50, or 2%. However this figure probably underestimates the actual value, as not all anglers are prepared to cut their hooks off if the hooks have become lodged in the gullet or gut. It is also likely that the higher level of angling skill among researchers conducting the hooking trials accounted for a lower incidence of deep-hooking than might be expected across the general angling community. 

Keywords: Released fish, Hook design, hooking injury, barotrauma, post-release survival, demersal fish species, reef line fishery, Coral Trout (Plectropomus leopardus), Redthroat Emperor (Lethrinus miniatus), Crimson Snapper (Lutjanus erythropterus), Saddletail Snapper (Lutjanus malabaricus), Red Emperor (Lutjanus sebae) and Spangled Emperor (Lethrinus nebulosus)

Final Report • 2011-11-24
2003-019-DLD.pdf

Summary

Experiments were conducted in northern, central and southern Queensland to investigate the effects of hook design and size on the incidence of hooking injury, and the effects of a number of factors, including barotrauma-treatment method, on post-release survival rates of a suite of key reef-associated demersal fish species of particular importance to Queensland’s reef line fishery. The key species examined were common coral trout (Plectropomus leopardus), redthroat emperor (Lethrinus miniatus), crimson snapper (Lutjanus erythropterus), saddletail snapper (Lutjanus malabaricus), red emperor (Lutjanus sebae) and spangled emperor (Lethrinus nebulosus).

The work comprised four components:
(i) Analysis of existing datasets in terms of discarding/release rates in the commercial, recreational and charter sectors and estimation of barotrauma treatment effects;
(ii) Field trials to determine experimentally the effects of three hook patterns (J-hooks, offset circles and non-offset circles) and two sizes (small: 4/0 or 5/0, and large: 8/0) on hooking injury, location of hook lodgment and catch rate;
(iii) Field experiments using specially-developed vertical floating enclosures to test short-term (3-day) survival rates of fish treated to relieve barotrauma by venting or shotline releasing;
(iv) A community-based tag-release-recapture experiment involving recreational anglers to test the effects of barotrauma treatment and other covariates on long-term (months to years) post-release survival.

Discarding rates of some species have increased since 1997 largely as a result of increases in legislated minimum legal size limits and the introduction of maximum size limits. In December 2003 the minimum legal size (MLS) limit for red emperor was raised significantly, from 45 cm (TL) to 55 cm. Concurrent increases in MLS of bluespot coral trout, redthroat emperor and spangled emperor did not result in an observable change in discard rate. By 2005 the reported recreational discarding rates for coral trout, redthroat emperor, spangled emperor and saddletail snapper ranged between 42% and 55%, but for crimson snapper the rate was 69%, and for red emperor it was 83%. Between 1989 and 2003 some 300–620 t of coral trout and 33–95 t of redthroat emperor were discarded annually by the commercial reef line fishery on the GBR. Modelling of potential high-grading after the introduction of a (competitive) total allowable commercial catch for coral trout indicated that discarding of this species could increase to as much as 3,900 t. Spatial (but not temporal) differences in discarding rates were significant, and modelling indicated a potential for large increases in discarding rates and subsequent cryptic mortality as a result of changes in management arrangements.

The effects of hook pattern varied between species, with no consistent significant trends. Across all species only a relatively small proportion of fish (< 4%) were deep-hooked (in the throat or gut). Small hooks (5/0 circle and 4/0 J-hooks) were more likely to lodge in the lip or mouth than large hooks, although the effect was weak. Crimson snapper were significantly less prone to damage from non-offset circle hooks than either of the other patterns, but the opposite trend occurred with saddletail snapper. There was also a weak tendency for coral trout to sustain more injuries when captured on J-hooks or offset circle hooks than on non-offset circles. Hook size showed a more consistent trend, with large (8/0) circle or J-hooks being more frequently associated with injury than small hooks in all species, but this was statistically significant only in coral trout and blackblotch emperor. 

Our controlled short-term (3-day) field experiments revealed that hook location was a major determinant of short-term survival in coral trout, crimson snapper and saddletail snapper. Even when the hooks were left in place according to best practice procedures, survival rates among deep-hooked fish were considerably reduced compared to those hooked in the mouth or lip. The modelled survival rates of shallow and deep-hooked fish repectively were as follows: coral trout 81 and 50%, redthroat emperor 86 and 59%, crimson snapper 96 and 35%, and saddletail snapper 73 and 38%. This represents an overall reduction across species in survival rate of around 50% as a result of deep hooking, even when the hooks were left in place. The results of our hooking damage experiment showed that the incidence of deep hooking was generally low across the species examined (< 4%), so that the predicted added mortality due to deep hooking would be in the order of 0.04 × 0.50, or 2%. However this figure probably underestimates the actual value, as not all anglers are prepared to cut their hooks off if the hooks have become lodged in the gullet or gut. It is also likely that the higher level of angling skill among researchers conducting the hooking trials accounted for a lower incidence of deep-hooking than might be expected across the general angling community. 

Keywords: Released fish, Hook design, hooking injury, barotrauma, post-release survival, demersal fish species, reef line fishery, Coral Trout (Plectropomus leopardus), Redthroat Emperor (Lethrinus miniatus), Crimson Snapper (Lutjanus erythropterus), Saddletail Snapper (Lutjanus malabaricus), Red Emperor (Lutjanus sebae) and Spangled Emperor (Lethrinus nebulosus)

Final Report • 2011-11-24
2003-019-DLD.pdf

Summary

Experiments were conducted in northern, central and southern Queensland to investigate the effects of hook design and size on the incidence of hooking injury, and the effects of a number of factors, including barotrauma-treatment method, on post-release survival rates of a suite of key reef-associated demersal fish species of particular importance to Queensland’s reef line fishery. The key species examined were common coral trout (Plectropomus leopardus), redthroat emperor (Lethrinus miniatus), crimson snapper (Lutjanus erythropterus), saddletail snapper (Lutjanus malabaricus), red emperor (Lutjanus sebae) and spangled emperor (Lethrinus nebulosus).

The work comprised four components:
(i) Analysis of existing datasets in terms of discarding/release rates in the commercial, recreational and charter sectors and estimation of barotrauma treatment effects;
(ii) Field trials to determine experimentally the effects of three hook patterns (J-hooks, offset circles and non-offset circles) and two sizes (small: 4/0 or 5/0, and large: 8/0) on hooking injury, location of hook lodgment and catch rate;
(iii) Field experiments using specially-developed vertical floating enclosures to test short-term (3-day) survival rates of fish treated to relieve barotrauma by venting or shotline releasing;
(iv) A community-based tag-release-recapture experiment involving recreational anglers to test the effects of barotrauma treatment and other covariates on long-term (months to years) post-release survival.

Discarding rates of some species have increased since 1997 largely as a result of increases in legislated minimum legal size limits and the introduction of maximum size limits. In December 2003 the minimum legal size (MLS) limit for red emperor was raised significantly, from 45 cm (TL) to 55 cm. Concurrent increases in MLS of bluespot coral trout, redthroat emperor and spangled emperor did not result in an observable change in discard rate. By 2005 the reported recreational discarding rates for coral trout, redthroat emperor, spangled emperor and saddletail snapper ranged between 42% and 55%, but for crimson snapper the rate was 69%, and for red emperor it was 83%. Between 1989 and 2003 some 300–620 t of coral trout and 33–95 t of redthroat emperor were discarded annually by the commercial reef line fishery on the GBR. Modelling of potential high-grading after the introduction of a (competitive) total allowable commercial catch for coral trout indicated that discarding of this species could increase to as much as 3,900 t. Spatial (but not temporal) differences in discarding rates were significant, and modelling indicated a potential for large increases in discarding rates and subsequent cryptic mortality as a result of changes in management arrangements.

The effects of hook pattern varied between species, with no consistent significant trends. Across all species only a relatively small proportion of fish (< 4%) were deep-hooked (in the throat or gut). Small hooks (5/0 circle and 4/0 J-hooks) were more likely to lodge in the lip or mouth than large hooks, although the effect was weak. Crimson snapper were significantly less prone to damage from non-offset circle hooks than either of the other patterns, but the opposite trend occurred with saddletail snapper. There was also a weak tendency for coral trout to sustain more injuries when captured on J-hooks or offset circle hooks than on non-offset circles. Hook size showed a more consistent trend, with large (8/0) circle or J-hooks being more frequently associated with injury than small hooks in all species, but this was statistically significant only in coral trout and blackblotch emperor. 

Our controlled short-term (3-day) field experiments revealed that hook location was a major determinant of short-term survival in coral trout, crimson snapper and saddletail snapper. Even when the hooks were left in place according to best practice procedures, survival rates among deep-hooked fish were considerably reduced compared to those hooked in the mouth or lip. The modelled survival rates of shallow and deep-hooked fish repectively were as follows: coral trout 81 and 50%, redthroat emperor 86 and 59%, crimson snapper 96 and 35%, and saddletail snapper 73 and 38%. This represents an overall reduction across species in survival rate of around 50% as a result of deep hooking, even when the hooks were left in place. The results of our hooking damage experiment showed that the incidence of deep hooking was generally low across the species examined (< 4%), so that the predicted added mortality due to deep hooking would be in the order of 0.04 × 0.50, or 2%. However this figure probably underestimates the actual value, as not all anglers are prepared to cut their hooks off if the hooks have become lodged in the gullet or gut. It is also likely that the higher level of angling skill among researchers conducting the hooking trials accounted for a lower incidence of deep-hooking than might be expected across the general angling community. 

Keywords: Released fish, Hook design, hooking injury, barotrauma, post-release survival, demersal fish species, reef line fishery, Coral Trout (Plectropomus leopardus), Redthroat Emperor (Lethrinus miniatus), Crimson Snapper (Lutjanus erythropterus), Saddletail Snapper (Lutjanus malabaricus), Red Emperor (Lutjanus sebae) and Spangled Emperor (Lethrinus nebulosus)

Related research

All research
research
Environment
Industry
Environment
PROJECT NUMBER • 2013-020
PROJECT STATUS:
COMPLETED

Physical oceanographic influences on Queensland reef fish and scallops

1. Review recent advances in the study of physical oceanographic influences on fisheries catch data, and describe the major physical oceanographic features that are likely to influence Queensland reef fish and saucer scallops.
ORGANISATION:
Department of Primary Industries (QLD)

Developing tagging models and validating assumptions for estimating key fishery assessment parameters in rock lobster fisheries

Project number: 2003-051
Project Status:
Completed
Budget expenditure: $409,509.00
Principal Investigator: Stewart Frusher
Organisation: University of Tasmania (UTAS)
Project start/end date: 19 Jul 2003 - 1 Jul 2007
Contact:
FRDC
TAGS
Wild Catch
Tagging
Stock Assessment
Mortality
Fishing Effort

Need

There is a common need in the assessment of all fisheries to obtain precise estimates of exploitation rates and/or biomass. In the Tasmanian rock lobster fishery, biomass is a key performance indicator and change in biomass is the primary driver for recommendations of future Total Allowable Commercial Catch (TACC) allocations by the Fisheries Advisory Committee. In recognition of this need, both the Tasmanian
Government (1992-1997) and FRDC (1997-2001) have funded projects to investigate methods to estimate biomass independent of the fishery.

Fishery independent estimates are essential because estimates derived from fisher’s catch and effort are often biased as exemplified by the change in the link between catch rate and abundance following the introduction of the ITQ management system in Tasmania (FRDC 1999/140). Although initially promising, exploitation rate and biomass estimates based on changes in the population during the fishing season proved unreliable (FRDC 1997/101). Both the Industry and Managers have identified the need to explore new methods to obtain precise estimates of these important performance indicators.

Multi-year tagging models have been identified as a promising way of estimating these parameters because they address the failings (variable catchability and recruitment) in the population derived estimators. Initial trials in northwestern Tasmania proved very successful and support the potential of this approach. However, tag returns from fishers are unpredictable and there is an immediate need to
determine ways of improving tag reporting rate to optimise the output of tag based models. Furthermore, the models applied to northwestern Tasmania relied on a minimum of two tagging events occurring each fishing season. As each tagging event occurred during a different period of the moult cycle, there is a need to validate the tag retention and tag induced mortality rates associated with these different tagging times. Other factors relating to size, sex, damage and their interactions with different tagging times also need further investigation. A careful evaluation of other means of improving the precision of estimates from tagging models is seen as necessary, prior to the implementation of a large scale tagging program.

Validating the assumptions associated with the use of tagging models, demonstrating ways to test for these assumptions and the precision of fishery assessment outputs is needed prior to recommending these models for use in other fisheries.

Objectives

1. To develop methods for maximising and better estimating tag reporting rate.
2. To evaluate different tagging methods in rock lobsters with respect to tag induced mortality, tag loss and the likelihood of recaptured tags being reported.
3. To determine the variability in tag loss, tag induced mortality and tag recapture rates associated with the time of tagging and demonstrate the impact that these have on mortality estimates.
4. To develop a fishery-based mark recapture model that estimates both fishing mortality and natural mortality and catchability, and demonstrates the precision of these parameters based on a number of data options.

Final report

ISBN: 978-1-86295-504-2
Author: Stewart Frusher
Final Report • 2017-09-29
2003-051-DLD.pdf

Summary

Tagging is an important tool for estimating key fisheries parameters such as fishing mortality, natural mortality and growth. This project identified the need for future tagging projects to undertake preliminary studies to determine the impact of tagging on both growth and survival, and we developed a new method for obtaining in situ measurements. While aquaria studies have demonstrated that the timing of tagging in relation to the lobster moult cycle can have an impact on tag-induced mortality, these studies estimated that the impacts were low. The in situ method in our study found similar moult cycle impacts but our impact estimates were substantially higher than previously considered.
 
New tagging projects for lobster should evaluate the use of PIT tags as this project demonstrated the ‘proof of concept’ in obtaining a 100% tag reporting rate by scanners placed at strategic locations on board fishing vessels. With as few as 10% of the fleet having scanners, PIT tagging proved to be cost beneficial compared to conventional T-bar tags. As PIT tags are normally imbedded in the muscle of an animal, they are ‘invisible’ to potential reporters (e.g. fishers). A hybrid T-bar tag developed and tested in this project combined a T-bar tag and a PIT tag so that the PIT tag remained visible to fishers for reporting on vessels that did not contain scanners. An additional benefit of the hybrid tag was that it removed the potential for the PIT tag to be ingested.
 
The development of an ‘exact time’ survival model that followed the fate of individual tags enables tagging programs to be more flexible in the release of tags. Previous multi-year tagging models required releases to be aggregated to a single release period during a specific tagging event (i.e. mean day of all releases for a tagging event). The new model allows for tagging projects to be more flexible in their design and incorporate tags released at any time. This would allow for inclusion of tagged animals released by fishers throughout the fishing season (e.g. berried female lobsters). The ‘exact time’ model also enabled finer scale (weeks, months etc) estimates of catchability to be estimated in addition to mortality rates, thus increasing the information obtained from a tagging study.
 
Final Report • 2017-09-29
2003-051-DLD.pdf

Summary

Tagging is an important tool for estimating key fisheries parameters such as fishing mortality, natural mortality and growth. This project identified the need for future tagging projects to undertake preliminary studies to determine the impact of tagging on both growth and survival, and we developed a new method for obtaining in situ measurements. While aquaria studies have demonstrated that the timing of tagging in relation to the lobster moult cycle can have an impact on tag-induced mortality, these studies estimated that the impacts were low. The in situ method in our study found similar moult cycle impacts but our impact estimates were substantially higher than previously considered.
 
New tagging projects for lobster should evaluate the use of PIT tags as this project demonstrated the ‘proof of concept’ in obtaining a 100% tag reporting rate by scanners placed at strategic locations on board fishing vessels. With as few as 10% of the fleet having scanners, PIT tagging proved to be cost beneficial compared to conventional T-bar tags. As PIT tags are normally imbedded in the muscle of an animal, they are ‘invisible’ to potential reporters (e.g. fishers). A hybrid T-bar tag developed and tested in this project combined a T-bar tag and a PIT tag so that the PIT tag remained visible to fishers for reporting on vessels that did not contain scanners. An additional benefit of the hybrid tag was that it removed the potential for the PIT tag to be ingested.
 
The development of an ‘exact time’ survival model that followed the fate of individual tags enables tagging programs to be more flexible in the release of tags. Previous multi-year tagging models required releases to be aggregated to a single release period during a specific tagging event (i.e. mean day of all releases for a tagging event). The new model allows for tagging projects to be more flexible in their design and incorporate tags released at any time. This would allow for inclusion of tagged animals released by fishers throughout the fishing season (e.g. berried female lobsters). The ‘exact time’ model also enabled finer scale (weeks, months etc) estimates of catchability to be estimated in addition to mortality rates, thus increasing the information obtained from a tagging study.
 
Final Report • 2017-09-29
2003-051-DLD.pdf

Summary

Tagging is an important tool for estimating key fisheries parameters such as fishing mortality, natural mortality and growth. This project identified the need for future tagging projects to undertake preliminary studies to determine the impact of tagging on both growth and survival, and we developed a new method for obtaining in situ measurements. While aquaria studies have demonstrated that the timing of tagging in relation to the lobster moult cycle can have an impact on tag-induced mortality, these studies estimated that the impacts were low. The in situ method in our study found similar moult cycle impacts but our impact estimates were substantially higher than previously considered.
 
New tagging projects for lobster should evaluate the use of PIT tags as this project demonstrated the ‘proof of concept’ in obtaining a 100% tag reporting rate by scanners placed at strategic locations on board fishing vessels. With as few as 10% of the fleet having scanners, PIT tagging proved to be cost beneficial compared to conventional T-bar tags. As PIT tags are normally imbedded in the muscle of an animal, they are ‘invisible’ to potential reporters (e.g. fishers). A hybrid T-bar tag developed and tested in this project combined a T-bar tag and a PIT tag so that the PIT tag remained visible to fishers for reporting on vessels that did not contain scanners. An additional benefit of the hybrid tag was that it removed the potential for the PIT tag to be ingested.
 
The development of an ‘exact time’ survival model that followed the fate of individual tags enables tagging programs to be more flexible in the release of tags. Previous multi-year tagging models required releases to be aggregated to a single release period during a specific tagging event (i.e. mean day of all releases for a tagging event). The new model allows for tagging projects to be more flexible in their design and incorporate tags released at any time. This would allow for inclusion of tagged animals released by fishers throughout the fishing season (e.g. berried female lobsters). The ‘exact time’ model also enabled finer scale (weeks, months etc) estimates of catchability to be estimated in addition to mortality rates, thus increasing the information obtained from a tagging study.
 
Final Report • 2017-09-29
2003-051-DLD.pdf

Summary

Tagging is an important tool for estimating key fisheries parameters such as fishing mortality, natural mortality and growth. This project identified the need for future tagging projects to undertake preliminary studies to determine the impact of tagging on both growth and survival, and we developed a new method for obtaining in situ measurements. While aquaria studies have demonstrated that the timing of tagging in relation to the lobster moult cycle can have an impact on tag-induced mortality, these studies estimated that the impacts were low. The in situ method in our study found similar moult cycle impacts but our impact estimates were substantially higher than previously considered.
 
New tagging projects for lobster should evaluate the use of PIT tags as this project demonstrated the ‘proof of concept’ in obtaining a 100% tag reporting rate by scanners placed at strategic locations on board fishing vessels. With as few as 10% of the fleet having scanners, PIT tagging proved to be cost beneficial compared to conventional T-bar tags. As PIT tags are normally imbedded in the muscle of an animal, they are ‘invisible’ to potential reporters (e.g. fishers). A hybrid T-bar tag developed and tested in this project combined a T-bar tag and a PIT tag so that the PIT tag remained visible to fishers for reporting on vessels that did not contain scanners. An additional benefit of the hybrid tag was that it removed the potential for the PIT tag to be ingested.
 
The development of an ‘exact time’ survival model that followed the fate of individual tags enables tagging programs to be more flexible in the release of tags. Previous multi-year tagging models required releases to be aggregated to a single release period during a specific tagging event (i.e. mean day of all releases for a tagging event). The new model allows for tagging projects to be more flexible in their design and incorporate tags released at any time. This would allow for inclusion of tagged animals released by fishers throughout the fishing season (e.g. berried female lobsters). The ‘exact time’ model also enabled finer scale (weeks, months etc) estimates of catchability to be estimated in addition to mortality rates, thus increasing the information obtained from a tagging study.
 
Final Report • 2017-09-29
2003-051-DLD.pdf

Summary

Tagging is an important tool for estimating key fisheries parameters such as fishing mortality, natural mortality and growth. This project identified the need for future tagging projects to undertake preliminary studies to determine the impact of tagging on both growth and survival, and we developed a new method for obtaining in situ measurements. While aquaria studies have demonstrated that the timing of tagging in relation to the lobster moult cycle can have an impact on tag-induced mortality, these studies estimated that the impacts were low. The in situ method in our study found similar moult cycle impacts but our impact estimates were substantially higher than previously considered.
 
New tagging projects for lobster should evaluate the use of PIT tags as this project demonstrated the ‘proof of concept’ in obtaining a 100% tag reporting rate by scanners placed at strategic locations on board fishing vessels. With as few as 10% of the fleet having scanners, PIT tagging proved to be cost beneficial compared to conventional T-bar tags. As PIT tags are normally imbedded in the muscle of an animal, they are ‘invisible’ to potential reporters (e.g. fishers). A hybrid T-bar tag developed and tested in this project combined a T-bar tag and a PIT tag so that the PIT tag remained visible to fishers for reporting on vessels that did not contain scanners. An additional benefit of the hybrid tag was that it removed the potential for the PIT tag to be ingested.
 
The development of an ‘exact time’ survival model that followed the fate of individual tags enables tagging programs to be more flexible in the release of tags. Previous multi-year tagging models required releases to be aggregated to a single release period during a specific tagging event (i.e. mean day of all releases for a tagging event). The new model allows for tagging projects to be more flexible in their design and incorporate tags released at any time. This would allow for inclusion of tagged animals released by fishers throughout the fishing season (e.g. berried female lobsters). The ‘exact time’ model also enabled finer scale (weeks, months etc) estimates of catchability to be estimated in addition to mortality rates, thus increasing the information obtained from a tagging study.
 
Final Report • 2017-09-29
2003-051-DLD.pdf

Summary

Tagging is an important tool for estimating key fisheries parameters such as fishing mortality, natural mortality and growth. This project identified the need for future tagging projects to undertake preliminary studies to determine the impact of tagging on both growth and survival, and we developed a new method for obtaining in situ measurements. While aquaria studies have demonstrated that the timing of tagging in relation to the lobster moult cycle can have an impact on tag-induced mortality, these studies estimated that the impacts were low. The in situ method in our study found similar moult cycle impacts but our impact estimates were substantially higher than previously considered.
 
New tagging projects for lobster should evaluate the use of PIT tags as this project demonstrated the ‘proof of concept’ in obtaining a 100% tag reporting rate by scanners placed at strategic locations on board fishing vessels. With as few as 10% of the fleet having scanners, PIT tagging proved to be cost beneficial compared to conventional T-bar tags. As PIT tags are normally imbedded in the muscle of an animal, they are ‘invisible’ to potential reporters (e.g. fishers). A hybrid T-bar tag developed and tested in this project combined a T-bar tag and a PIT tag so that the PIT tag remained visible to fishers for reporting on vessels that did not contain scanners. An additional benefit of the hybrid tag was that it removed the potential for the PIT tag to be ingested.
 
The development of an ‘exact time’ survival model that followed the fate of individual tags enables tagging programs to be more flexible in the release of tags. Previous multi-year tagging models required releases to be aggregated to a single release period during a specific tagging event (i.e. mean day of all releases for a tagging event). The new model allows for tagging projects to be more flexible in their design and incorporate tags released at any time. This would allow for inclusion of tagged animals released by fishers throughout the fishing season (e.g. berried female lobsters). The ‘exact time’ model also enabled finer scale (weeks, months etc) estimates of catchability to be estimated in addition to mortality rates, thus increasing the information obtained from a tagging study.
 
Final Report • 2017-09-29
2003-051-DLD.pdf

Summary

Tagging is an important tool for estimating key fisheries parameters such as fishing mortality, natural mortality and growth. This project identified the need for future tagging projects to undertake preliminary studies to determine the impact of tagging on both growth and survival, and we developed a new method for obtaining in situ measurements. While aquaria studies have demonstrated that the timing of tagging in relation to the lobster moult cycle can have an impact on tag-induced mortality, these studies estimated that the impacts were low. The in situ method in our study found similar moult cycle impacts but our impact estimates were substantially higher than previously considered.
 
New tagging projects for lobster should evaluate the use of PIT tags as this project demonstrated the ‘proof of concept’ in obtaining a 100% tag reporting rate by scanners placed at strategic locations on board fishing vessels. With as few as 10% of the fleet having scanners, PIT tagging proved to be cost beneficial compared to conventional T-bar tags. As PIT tags are normally imbedded in the muscle of an animal, they are ‘invisible’ to potential reporters (e.g. fishers). A hybrid T-bar tag developed and tested in this project combined a T-bar tag and a PIT tag so that the PIT tag remained visible to fishers for reporting on vessels that did not contain scanners. An additional benefit of the hybrid tag was that it removed the potential for the PIT tag to be ingested.
 
The development of an ‘exact time’ survival model that followed the fate of individual tags enables tagging programs to be more flexible in the release of tags. Previous multi-year tagging models required releases to be aggregated to a single release period during a specific tagging event (i.e. mean day of all releases for a tagging event). The new model allows for tagging projects to be more flexible in their design and incorporate tags released at any time. This would allow for inclusion of tagged animals released by fishers throughout the fishing season (e.g. berried female lobsters). The ‘exact time’ model also enabled finer scale (weeks, months etc) estimates of catchability to be estimated in addition to mortality rates, thus increasing the information obtained from a tagging study.
 
Final Report • 2017-09-29
2003-051-DLD.pdf

Summary

Tagging is an important tool for estimating key fisheries parameters such as fishing mortality, natural mortality and growth. This project identified the need for future tagging projects to undertake preliminary studies to determine the impact of tagging on both growth and survival, and we developed a new method for obtaining in situ measurements. While aquaria studies have demonstrated that the timing of tagging in relation to the lobster moult cycle can have an impact on tag-induced mortality, these studies estimated that the impacts were low. The in situ method in our study found similar moult cycle impacts but our impact estimates were substantially higher than previously considered.
 
New tagging projects for lobster should evaluate the use of PIT tags as this project demonstrated the ‘proof of concept’ in obtaining a 100% tag reporting rate by scanners placed at strategic locations on board fishing vessels. With as few as 10% of the fleet having scanners, PIT tagging proved to be cost beneficial compared to conventional T-bar tags. As PIT tags are normally imbedded in the muscle of an animal, they are ‘invisible’ to potential reporters (e.g. fishers). A hybrid T-bar tag developed and tested in this project combined a T-bar tag and a PIT tag so that the PIT tag remained visible to fishers for reporting on vessels that did not contain scanners. An additional benefit of the hybrid tag was that it removed the potential for the PIT tag to be ingested.
 
The development of an ‘exact time’ survival model that followed the fate of individual tags enables tagging programs to be more flexible in the release of tags. Previous multi-year tagging models required releases to be aggregated to a single release period during a specific tagging event (i.e. mean day of all releases for a tagging event). The new model allows for tagging projects to be more flexible in their design and incorporate tags released at any time. This would allow for inclusion of tagged animals released by fishers throughout the fishing season (e.g. berried female lobsters). The ‘exact time’ model also enabled finer scale (weeks, months etc) estimates of catchability to be estimated in addition to mortality rates, thus increasing the information obtained from a tagging study.
 
Final Report • 2017-09-29
2003-051-DLD.pdf

Summary

Tagging is an important tool for estimating key fisheries parameters such as fishing mortality, natural mortality and growth. This project identified the need for future tagging projects to undertake preliminary studies to determine the impact of tagging on both growth and survival, and we developed a new method for obtaining in situ measurements. While aquaria studies have demonstrated that the timing of tagging in relation to the lobster moult cycle can have an impact on tag-induced mortality, these studies estimated that the impacts were low. The in situ method in our study found similar moult cycle impacts but our impact estimates were substantially higher than previously considered.
 
New tagging projects for lobster should evaluate the use of PIT tags as this project demonstrated the ‘proof of concept’ in obtaining a 100% tag reporting rate by scanners placed at strategic locations on board fishing vessels. With as few as 10% of the fleet having scanners, PIT tagging proved to be cost beneficial compared to conventional T-bar tags. As PIT tags are normally imbedded in the muscle of an animal, they are ‘invisible’ to potential reporters (e.g. fishers). A hybrid T-bar tag developed and tested in this project combined a T-bar tag and a PIT tag so that the PIT tag remained visible to fishers for reporting on vessels that did not contain scanners. An additional benefit of the hybrid tag was that it removed the potential for the PIT tag to be ingested.
 
The development of an ‘exact time’ survival model that followed the fate of individual tags enables tagging programs to be more flexible in the release of tags. Previous multi-year tagging models required releases to be aggregated to a single release period during a specific tagging event (i.e. mean day of all releases for a tagging event). The new model allows for tagging projects to be more flexible in their design and incorporate tags released at any time. This would allow for inclusion of tagged animals released by fishers throughout the fishing season (e.g. berried female lobsters). The ‘exact time’ model also enabled finer scale (weeks, months etc) estimates of catchability to be estimated in addition to mortality rates, thus increasing the information obtained from a tagging study.
 
Final Report • 2017-09-29
2003-051-DLD.pdf

Summary

Tagging is an important tool for estimating key fisheries parameters such as fishing mortality, natural mortality and growth. This project identified the need for future tagging projects to undertake preliminary studies to determine the impact of tagging on both growth and survival, and we developed a new method for obtaining in situ measurements. While aquaria studies have demonstrated that the timing of tagging in relation to the lobster moult cycle can have an impact on tag-induced mortality, these studies estimated that the impacts were low. The in situ method in our study found similar moult cycle impacts but our impact estimates were substantially higher than previously considered.
 
New tagging projects for lobster should evaluate the use of PIT tags as this project demonstrated the ‘proof of concept’ in obtaining a 100% tag reporting rate by scanners placed at strategic locations on board fishing vessels. With as few as 10% of the fleet having scanners, PIT tagging proved to be cost beneficial compared to conventional T-bar tags. As PIT tags are normally imbedded in the muscle of an animal, they are ‘invisible’ to potential reporters (e.g. fishers). A hybrid T-bar tag developed and tested in this project combined a T-bar tag and a PIT tag so that the PIT tag remained visible to fishers for reporting on vessels that did not contain scanners. An additional benefit of the hybrid tag was that it removed the potential for the PIT tag to be ingested.
 
The development of an ‘exact time’ survival model that followed the fate of individual tags enables tagging programs to be more flexible in the release of tags. Previous multi-year tagging models required releases to be aggregated to a single release period during a specific tagging event (i.e. mean day of all releases for a tagging event). The new model allows for tagging projects to be more flexible in their design and incorporate tags released at any time. This would allow for inclusion of tagged animals released by fishers throughout the fishing season (e.g. berried female lobsters). The ‘exact time’ model also enabled finer scale (weeks, months etc) estimates of catchability to be estimated in addition to mortality rates, thus increasing the information obtained from a tagging study.
 
Final Report • 2017-09-29
2003-051-DLD.pdf

Summary

Tagging is an important tool for estimating key fisheries parameters such as fishing mortality, natural mortality and growth. This project identified the need for future tagging projects to undertake preliminary studies to determine the impact of tagging on both growth and survival, and we developed a new method for obtaining in situ measurements. While aquaria studies have demonstrated that the timing of tagging in relation to the lobster moult cycle can have an impact on tag-induced mortality, these studies estimated that the impacts were low. The in situ method in our study found similar moult cycle impacts but our impact estimates were substantially higher than previously considered.
 
New tagging projects for lobster should evaluate the use of PIT tags as this project demonstrated the ‘proof of concept’ in obtaining a 100% tag reporting rate by scanners placed at strategic locations on board fishing vessels. With as few as 10% of the fleet having scanners, PIT tagging proved to be cost beneficial compared to conventional T-bar tags. As PIT tags are normally imbedded in the muscle of an animal, they are ‘invisible’ to potential reporters (e.g. fishers). A hybrid T-bar tag developed and tested in this project combined a T-bar tag and a PIT tag so that the PIT tag remained visible to fishers for reporting on vessels that did not contain scanners. An additional benefit of the hybrid tag was that it removed the potential for the PIT tag to be ingested.
 
The development of an ‘exact time’ survival model that followed the fate of individual tags enables tagging programs to be more flexible in the release of tags. Previous multi-year tagging models required releases to be aggregated to a single release period during a specific tagging event (i.e. mean day of all releases for a tagging event). The new model allows for tagging projects to be more flexible in their design and incorporate tags released at any time. This would allow for inclusion of tagged animals released by fishers throughout the fishing season (e.g. berried female lobsters). The ‘exact time’ model also enabled finer scale (weeks, months etc) estimates of catchability to be estimated in addition to mortality rates, thus increasing the information obtained from a tagging study.
 

Evaluation of crystal crab resource from Cape Leeuwin to the WA/SA border.

Project number: 2003-077
Project Status:
Completed
Budget expenditure: $74,480.00
Principal Investigator: Richard N. Stevens
Organisation: Western Australian Fishing Industry Council Inc (WAFIC)
Project start/end date: 25 Oct 2003 - 30 May 2006
Contact:
FRDC
TAGS
Wild Catch
Tagging
Survey
Population Dynamics
Physiology
SPECIES
Snow Crabs

Need

The fishermen on the South Coast have recognised that a resource of Crystal Crabs exists between Cape Leeuwin and the SA border. In order to develop the resource to its optimum potential there is first a need to determine the size and extent of the crab stocks. Thus development of this new species for this 1,500Km of coastline can be developed in an orderly manner.

Objectives

1. To determine the size frequency distribution and relative densities of crystal crab off the south coast of the State between the Western Australian/South Australian border and Cape Leeuwin through the use of a pot survey.
2. To tag 1,000 crabs covering a range of sizes for growth and movement data
3. Determine the extent to which sea lice affect the catches of crystal crab on the south coast of Western Australia, by the use of proven bait saving devices.
4. To determine the effect of different sized traps on the catchability of crystal crab.

Final report

ISBN: 0-86905-876-2
Author: Richard Stevens
Final Report • 2006-07-24 • 1.06 MB
2003-077-DLD.pdf

Summary

The licensed crustacean fishermen on the south coast of Western Australia recognised that a resource of Crystal Crab, Chaceon bicolor existed between Cape Leeuwin (ca 115º E) and the South Australian border (129º E).  In order to develop this resource to its optimum and sustainable potential, there was first a need to determine the relative abundance and distribution of this species in that region.  Since a substantial commercial fishery for this species exists on the west coast of the state, it was important to collect data from the south coast that could be compared with data from the existing west coast fishery in order to estimate a sustainable annual yield for the south coast fishery based on the catch return data from the west coast fishery.  The relative abundance and distribution and size distribution of Crystal Crab have thus been studied on the south coast of Western Australia between approximately 115º 20’ and 123º E, data that has not previously been available.
Final Report • 2006-07-24 • 1.06 MB
2003-077-DLD.pdf

Summary

The licensed crustacean fishermen on the south coast of Western Australia recognised that a resource of Crystal Crab, Chaceon bicolor existed between Cape Leeuwin (ca 115º E) and the South Australian border (129º E).  In order to develop this resource to its optimum and sustainable potential, there was first a need to determine the relative abundance and distribution of this species in that region.  Since a substantial commercial fishery for this species exists on the west coast of the state, it was important to collect data from the south coast that could be compared with data from the existing west coast fishery in order to estimate a sustainable annual yield for the south coast fishery based on the catch return data from the west coast fishery.  The relative abundance and distribution and size distribution of Crystal Crab have thus been studied on the south coast of Western Australia between approximately 115º 20’ and 123º E, data that has not previously been available.
Final Report • 2006-07-24 • 1.06 MB
2003-077-DLD.pdf

Summary

The licensed crustacean fishermen on the south coast of Western Australia recognised that a resource of Crystal Crab, Chaceon bicolor existed between Cape Leeuwin (ca 115º E) and the South Australian border (129º E).  In order to develop this resource to its optimum and sustainable potential, there was first a need to determine the relative abundance and distribution of this species in that region.  Since a substantial commercial fishery for this species exists on the west coast of the state, it was important to collect data from the south coast that could be compared with data from the existing west coast fishery in order to estimate a sustainable annual yield for the south coast fishery based on the catch return data from the west coast fishery.  The relative abundance and distribution and size distribution of Crystal Crab have thus been studied on the south coast of Western Australia between approximately 115º 20’ and 123º E, data that has not previously been available.
Final Report • 2006-07-24 • 1.06 MB
2003-077-DLD.pdf

Summary

The licensed crustacean fishermen on the south coast of Western Australia recognised that a resource of Crystal Crab, Chaceon bicolor existed between Cape Leeuwin (ca 115º E) and the South Australian border (129º E).  In order to develop this resource to its optimum and sustainable potential, there was first a need to determine the relative abundance and distribution of this species in that region.  Since a substantial commercial fishery for this species exists on the west coast of the state, it was important to collect data from the south coast that could be compared with data from the existing west coast fishery in order to estimate a sustainable annual yield for the south coast fishery based on the catch return data from the west coast fishery.  The relative abundance and distribution and size distribution of Crystal Crab have thus been studied on the south coast of Western Australia between approximately 115º 20’ and 123º E, data that has not previously been available.
Final Report • 2006-07-24 • 1.06 MB
2003-077-DLD.pdf

Summary

The licensed crustacean fishermen on the south coast of Western Australia recognised that a resource of Crystal Crab, Chaceon bicolor existed between Cape Leeuwin (ca 115º E) and the South Australian border (129º E).  In order to develop this resource to its optimum and sustainable potential, there was first a need to determine the relative abundance and distribution of this species in that region.  Since a substantial commercial fishery for this species exists on the west coast of the state, it was important to collect data from the south coast that could be compared with data from the existing west coast fishery in order to estimate a sustainable annual yield for the south coast fishery based on the catch return data from the west coast fishery.  The relative abundance and distribution and size distribution of Crystal Crab have thus been studied on the south coast of Western Australia between approximately 115º 20’ and 123º E, data that has not previously been available.
Final Report • 2006-07-24 • 1.06 MB
2003-077-DLD.pdf

Summary

The licensed crustacean fishermen on the south coast of Western Australia recognised that a resource of Crystal Crab, Chaceon bicolor existed between Cape Leeuwin (ca 115º E) and the South Australian border (129º E).  In order to develop this resource to its optimum and sustainable potential, there was first a need to determine the relative abundance and distribution of this species in that region.  Since a substantial commercial fishery for this species exists on the west coast of the state, it was important to collect data from the south coast that could be compared with data from the existing west coast fishery in order to estimate a sustainable annual yield for the south coast fishery based on the catch return data from the west coast fishery.  The relative abundance and distribution and size distribution of Crystal Crab have thus been studied on the south coast of Western Australia between approximately 115º 20’ and 123º E, data that has not previously been available.
Final Report • 2006-07-24 • 1.06 MB
2003-077-DLD.pdf

Summary

The licensed crustacean fishermen on the south coast of Western Australia recognised that a resource of Crystal Crab, Chaceon bicolor existed between Cape Leeuwin (ca 115º E) and the South Australian border (129º E).  In order to develop this resource to its optimum and sustainable potential, there was first a need to determine the relative abundance and distribution of this species in that region.  Since a substantial commercial fishery for this species exists on the west coast of the state, it was important to collect data from the south coast that could be compared with data from the existing west coast fishery in order to estimate a sustainable annual yield for the south coast fishery based on the catch return data from the west coast fishery.  The relative abundance and distribution and size distribution of Crystal Crab have thus been studied on the south coast of Western Australia between approximately 115º 20’ and 123º E, data that has not previously been available.
Final Report • 2006-07-24 • 1.06 MB
2003-077-DLD.pdf

Summary

The licensed crustacean fishermen on the south coast of Western Australia recognised that a resource of Crystal Crab, Chaceon bicolor existed between Cape Leeuwin (ca 115º E) and the South Australian border (129º E).  In order to develop this resource to its optimum and sustainable potential, there was first a need to determine the relative abundance and distribution of this species in that region.  Since a substantial commercial fishery for this species exists on the west coast of the state, it was important to collect data from the south coast that could be compared with data from the existing west coast fishery in order to estimate a sustainable annual yield for the south coast fishery based on the catch return data from the west coast fishery.  The relative abundance and distribution and size distribution of Crystal Crab have thus been studied on the south coast of Western Australia between approximately 115º 20’ and 123º E, data that has not previously been available.
Final Report • 2006-07-24 • 1.06 MB
2003-077-DLD.pdf

Summary

The licensed crustacean fishermen on the south coast of Western Australia recognised that a resource of Crystal Crab, Chaceon bicolor existed between Cape Leeuwin (ca 115º E) and the South Australian border (129º E).  In order to develop this resource to its optimum and sustainable potential, there was first a need to determine the relative abundance and distribution of this species in that region.  Since a substantial commercial fishery for this species exists on the west coast of the state, it was important to collect data from the south coast that could be compared with data from the existing west coast fishery in order to estimate a sustainable annual yield for the south coast fishery based on the catch return data from the west coast fishery.  The relative abundance and distribution and size distribution of Crystal Crab have thus been studied on the south coast of Western Australia between approximately 115º 20’ and 123º E, data that has not previously been available.
Final Report • 2006-07-24 • 1.06 MB
2003-077-DLD.pdf

Summary

The licensed crustacean fishermen on the south coast of Western Australia recognised that a resource of Crystal Crab, Chaceon bicolor existed between Cape Leeuwin (ca 115º E) and the South Australian border (129º E).  In order to develop this resource to its optimum and sustainable potential, there was first a need to determine the relative abundance and distribution of this species in that region.  Since a substantial commercial fishery for this species exists on the west coast of the state, it was important to collect data from the south coast that could be compared with data from the existing west coast fishery in order to estimate a sustainable annual yield for the south coast fishery based on the catch return data from the west coast fishery.  The relative abundance and distribution and size distribution of Crystal Crab have thus been studied on the south coast of Western Australia between approximately 115º 20’ and 123º E, data that has not previously been available.
Final Report • 2006-07-24 • 1.06 MB
2003-077-DLD.pdf

Summary

The licensed crustacean fishermen on the south coast of Western Australia recognised that a resource of Crystal Crab, Chaceon bicolor existed between Cape Leeuwin (ca 115º E) and the South Australian border (129º E).  In order to develop this resource to its optimum and sustainable potential, there was first a need to determine the relative abundance and distribution of this species in that region.  Since a substantial commercial fishery for this species exists on the west coast of the state, it was important to collect data from the south coast that could be compared with data from the existing west coast fishery in order to estimate a sustainable annual yield for the south coast fishery based on the catch return data from the west coast fishery.  The relative abundance and distribution and size distribution of Crystal Crab have thus been studied on the south coast of Western Australia between approximately 115º 20’ and 123º E, data that has not previously been available.