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People
PROJECT NUMBER • 1993-115
PROJECT STATUS:
COMPLETED

Workshop on spawning stock-recruitment relationships (SRRs) in Australian crustacean fisheries

The relationship between spawning stock size and the size of the subsequent recruitment is fundamental to fisheries science. Without a working knowledge of the relationship it is not possible to know how heavily a spawning stock can be fished before recruitment levels begin to decline. Although...
ORGANISATION:
Department of Primary Industries (QLD)

Population dynamics and management of spanner crabs in southern Queensland

Project number: 1995-022
Project Status:
Completed
Budget expenditure: $262,552.00
Principal Investigator: Ian Brown
Organisation: Department of Primary Industries (QLD)
Project start/end date: 18 Dec 1995 - 30 Jun 2000
Contact:
FRDC

Objectives

1. To estimate the size of the south Queensland spanner crab stock.
2. Determine the appropriateness of existing spawning closure arrangements.
3. To determine whether catch size-distribution can be used to estimate population age-structure and growth rates.
4. To evaluate the impact of post-discard mortality amongst sub-legal crabs on yields, and promote the development (by industry) of less damaging apparatus.

Final report

Authors: Ian Brown John Kirkwood Shane Gaddes Cathy Dichmont & Jenny Ovenden
Final Report • 1999-09-01 • 13.01 MB
1995-022-DLD.pdf

Summary

Spanner crabs (Ranina ranina) represent a valuable resource to southern Queensland and northern NSW. The fishery became established in the late 1970s, and as a result of an almost exponential increase in fishing effort between 1992 and 1995 an output-controlled limited entry management arrangement was introduced. During that period catches increased from about 800 to over 3,000 t, as the fishery expanded northwards to previously unexploited grounds, and a profitable live-export market was developed in south-east Asia.
The Queensland fleet comprises some 240 vessels specifically licenced to take spanner crabs in Managed Area A, which is subject to a Total Allowable Commercial Catch (TACC), currently set at 2600 t. Another 310 vessels are licenced to fish only in Managed Area B (north of the main fishing grounds) where the TACC does not apply. At present the TACC is competitive, but in the near future an Individual Transferrable Quota (ITQ) system is to be introduced.
Trends in commercial fisheries catch-effort statistics indicate that the spanner crab stock in southern Queensland is currently being harvested at a sustainable level. However several questions remain with respect to the application of the commercial logbook data, possibly the most important of which is how well commercial catch-per-unit-effoti represents stock abundance. The spatial distribution of spanner crabs is patchy, and the fishery operates such that patches are located, targeted and fished down. This can potentially lead to a situation of hyperstability, where the stock is actually declining despite catch rates remaining constant. This highlights the expected value of the fishery-independent monitoring programme currently being planned by QDPI with (in the case of the spanner crab fishery) a significant level of cost-recovery from industry.
Previous attempts to estimate growth rate of spanner crabs resulted in little consensus, due in part to inadequate sample sizes (length-based methods) and uncertainty surrounding the effects of tagging on growth (tag-recapture methods). Our initial objective was to determine whether the length-based methods would work if the samples were very large.
 
Variability in the size-structure of even very large samples of adult crabs was so great that we could place little confidence in growth estimates obtained from this type of data. Because of this, we negotiated a change in research direction with FRDC, focussing on two alternative approaches to the question of growth rates. The first was to investigate growth in pre-recruits. The second was to quantify the likely effect of tagging on moulting and growth, and to determine the extent of growth rate differences between NSW and Queensland.
Very small spanner crabs are not taken by baited tangle nets, regardless of mesh size, so a different sampling arrangement was required. A two-track channel dredge was successful in capturing intact megalopae and early juvenile stages, which provided length frequency data of considerable value to estimating pre-recruit growth. However because of its small size only very limited samples were able to be collected. To increase the sampling volume we developed a substantially larger, hydraulically­assisted dredge. This device has been field-tested on several occasions, but it has not yet been developed and used to full effect.
Laboratory experiments demonstrated that tagging had an adverse effect on weight increase and survival of spanner crabs, suggesting that growth rate estimates based on mark-recapture techniques may be biased. Of the several different types tested, anchor tags were superior in terms of ease of application and visibility. Recognising that the results may be biased, we released 4,804 tagged crabs at sites throughout the fishing grounds, to determine whether growth of spanner crabs in Queensland waters is significantly different from that in NSW, reported in a previous study. Fourteen of the 221 crabs recaptured in 1998 had moulted, with growth male growth increments being greater than those offemales (X = 11.86 and 7.40 mm respectively). Recapture rates were significantly higher for males than females, and were also significantly greater for larger individuals of each sex. This suggests that tag mortality was greater in the smaller size-classes. Recaptured crabs had moved distances ranging from O to 45 km since release, but showed no tendency to move in any particular direction.
Our length-based assessment model has not yet been successful in producing useful estimates of the relevant stock performance indicators for use by management. This was due to the lack of contrast in the CPUE data, the relatively short data time-series, the extreme spatial and temporal variability in population size-structure and sex-ratio as represented in commercial catches and research samples, and the absence of definitive growth data.
Mitochondrial DNA analysis indicated that the east-coast spanner crab fishery comprises a single unit stock, and there thus appears to be no biological justification for separate management arrangements in different geographic areas.
 
Analysis of reproductive chronology indicates that the timing of the existing spawning closure is appropriate for minimising mortality amongst egg-bearing female spanner crabs across the entire fishery, and we recommend that the closure be retained in legislation.
 
Exploratory surveys for spanner crabs conducted in two areas outside the current fishing grounds did not reveal any significant quantity of crabs, although small numbers were captured at two sites amongst the Swain Reefs. From the available information it seems unlikely that there are any major unexploited populations of spanner crabs remaining in Queensland waters.
We have demonstrated that limb damage to undersized discarded spanner crabs has a major effect on their survival under natural conditions. Poor handling practices in the fishery result in considerable mortality amongst discarded small crabs, highlighting the need for continuing fisher education and ongoing investigation of alternative catching apparatus.
 
The two major issues for further research into the spanner crab fishery are (i) deriving a robust estimate of the species' growth rate, (ii) investigating the source of the extreme variability in size­frequency and sex-ratios in population samples.
People
Adoption
PROJECT NUMBER • 1998-418
PROJECT STATUS:
COMPLETED

'99 Innovations for seafood - an international conference

Innovation is a key topic in the competitive economic environment. Innovative actions need to be recognised and encouraged. A dedicated seafood post harvest conference was the ideal opportunity to present innovative ideas and processes from the Australian industry and gain benefit from hearing the...
ORGANISATION:
Department of Primary Industries (QLD)

Publication of "Proceedings from the 2nd Australasian Scallop Workshop"

Project number: 1992-092
Project Status:
Completed
Budget expenditure: $19,370.69
Principal Investigator: Mike Dredge
Organisation: Department of Primary Industries (QLD)
Project start/end date: 11 Oct 1992 - 30 Jun 1995
Contact:
FRDC

Objectives

1. Disseminate information on the status of significant fisheries and mariculture ventures involving scallops throughout Australasia

Final report

Author: Mike Dredge
Final Report • 1994-09-23 • 4.33 MB
1992-092-DLD.pdf

Summary

The First Australasian Scallop Workshop was held in Taroona, Tasmania in July 1988 and was attended by 51 participants from Australia, New Zealand and Japan.

It proved to be a very valuable forum for exchange of ideas on scallop biology, management and culture. The organisers of that workshop, Mike Dredge, Will Zacharin and Lindsay loll, along with Richard McLoughlin must be thanked again for taking the initiative in organising the second Australasian Scallop Workshop at the East Coaster Resort, Triabunna, Tasmania, 23-25 March 1993.

Support for the second Australasian Workshop has been provided by the Fishing Industry Research and Development Corporation, the Commonwealth Department of lndustry Technology Employment and Commerce, state departments responsible for fisheries in Queensland, Western Australia and Tasmania, and the CSIRO Division of Fisheries. Thanks for this support are extended to each of those bodies, in the context of both the workshop and publication of the proceedings.

Scallop resources are notoriously difficult to manage because of wide fluctuations in recruitment and problems with harvesting technology; this emphasises the need for workshops of this nature to obtain maximum benefit from dissemination of knowledge and experience in scallop biology and management.

Recently we have seen progress towards more rational management of scallop resources in this part of the world and for the first time in southeastern Australia there appears to be a cooperative and constructive approach to scallop fishery management. While scallop stocks in Victoria and Tasmania have been in decline in recent years, the saucer scallop fisheries in Western Australia and Queensland have stabilised or are expanding. The background to such variation, and of the associated problems of recruitment variability in scallops from W.A. to Tasmania are discussed in some detail.

It is pleasing to note also that an appropriate time allocation has been made towards considering the impact of our scallop harvesting technology, both on the scallops themselves and on the environment which sustains them. It is clear that the industry cannot afford to continue using inefficient and destructive fishing gear if better technology is available.

The workshop was perfectly placed in Triabunna to explore recent progress in scallop culture and reseeding. Free exchange of ideas on methodology and technology relating to these activities shows promise that scallop enhancement may achieve its full potential in the coming years. The enhancement project in Tasmania has been operating since 1987 and all types of difficulties from appropriate gear to aspects of marketing are still being researched by the company.

This workshop provided an opportunity for biologists, managers, marine farmers, fishers and others with an interest in scallops to expand their understanding of scallops and pass on some of their hard earned knowledge and experience to others.

The make-up of this workshop is unusual, to say the least, in that organisers have brought together so many facets of industry and have recognised the importance of marketing to the scallop fisheries.

Finally, some public health issues associated with scallop fisheries around the world have been brought to the workshop's attention. Such issues, largely associated with dinoflagellate-derived toxins, have not been a major issue in Australia to this time. Their significance in an international context, and their potential to affect scallop marketing and fisheries in Australia, is a major consideration for the future.

Industry
PROJECT NUMBER • 1992-071
PROJECT STATUS:
COMPLETED

Live transport of crustaceans in air - prolonging the survival of crabs

We studied the live transport of crustaceans in air, using the spanner crab Ranina ranina as an example, and developed guidelines for handling live spanner crabs which we presented to an industry workshop. Our findings were also of general relevance to the live shipment of other oceanic crab...
ORGANISATION:
Department of Primary Industries (QLD)
Environment
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