Developing improved methods for stock assessment in spatially complex fisheries using Blue-eye Trevalla as a case study
There is considerable scope to enhance spatially-based management arrangements for species with broad or disjunct distributions, or species that are targeted by different gears in different areas or habitats. For example, current SESSF management arrangements do not consider stock structure in Blue-eye Trevalla, although it ranges from WA to Queensland and beyond Australian waters, and preliminary analysis showed some evidence for separate stocks between the SESSF and ECDW seamounts. There is an immediate need to develop and incorporate new spatially-based arrangements into management of Blue-eye Trevalla in response to complex spatial patterns in the fishery that include a change of fishing methods through time, whale interactions increasing in some areas, re-location of effort into underutilized locations (e.g. ECDF seamounts), and the series of recent and planned area closures that include Commonwealth Marine Reserves (CMR) in the GAB, off the eastern seaboard and on the offshore Tasmantid Seamount Chain, and fishery closures being implemented by AFMA and NSW Fisheries to project Harrisson’s and Southern Dogfish. There is a more general need to assess options for managing separate stocks of other species – such as regionalising TAC’s – and to evaluate options against EBFM performance measures that include economic and environmental indicators.
Final report
Research to underpin better understanding and management of western gemfish stocks in the Great Australian Bight
The CTS and GABTS operate in geographically separate areas and have different catch and effort histories. Analysed separately, both fisheries show substantially different levels of exploitation and depletion of gemfish. The recent quantitative assessment combines both sectors and provides a single RBC.
The rationale for combining both stocks is based on previous genetic research (Colgan and Paxton, 1997) suggesting there is a single unit stock for western gemfish, which is independent from eastern gemfish. However, their results may not accurately reflect extant population subdivision for gemfish in the Bass Strait area and westwards. Few locations were sampled in this area by the Colgan and Paxton study, sample sizes per location were low and the power of their genetic analysis was well below what can now be achieved with the latest technology.
The lack of accurate information on the biological stock structure of western gemfish is confounding assessment, management and allocation of the resource between fisheries.
A study incorporating more robust genetic data (larger sample sizes and two different genetic markers), is likely to provide a more definitive clarification of population structuring for this stock. These data can also clarify the boundary between western gemfish and overfished eastern gemfish. Analysis of gonad index and length frequency data are likely to improve our understanding of the timing and spatial extent of spawning for this species, and assist in defining spawning populations of gemfish. These results will directly inform management boundaries, stock assessment analyses, the setting of RBCs and TACs, the apportionment of catch and our understanding of the movement and spawning of this species.
Final report
Gemfish (Rexea solandri) is a benthopelagic snake mackerel of the Family Gempylidae. Gemfish is found on the continental shelf and slope in southern, southwestern and southeastern Australia and New Zealand. It is found at depths ranging from 100 to 800 metres, but commonly at 300 to 450 metres. Historically Gemfish formed part of a large trawl fishery off the east coast of Australia in the 1970s and 1980s. Catches peaked between 1978 and 1980 at around 5,000 tonnes per year, declining substantially after 1987. The east coast fishery remains in an overfished state with an unavoidable bycatch limit of 100 T. The most recent stock assessment estimated spawning biomass at 15 per cent of the 1968 level.
Fisheries for Gemfish have operated off western Tasmania, south western Victoria and south eastern South Australia as part of the Commonwealth Trawl Sector (CTS) of the Southern and Eastern Scalefish and Shark Fishery (SESSF) and in Great Australian Bight as part of the Great Australian Bight Trawl Sector (GABTS) of the SESSF. These fisheries are managed as a separate stock to the east coast and have a substantially different fishing history and level of exploitation. The most recent stock assessment of the western stock suggested biomass is at 74 per cent of virgin biomass levels.
Great Australian Bight Resources Assessment Group (GABRAG) had sufficient concerns regarding the population structure of the western stock and its impact on the stock assessment (whether western Gemfish constituted a single population and where the boundary between east and west arises) to reject the assessment.
Previous research found genetic subdivision between the eastern stock of Gemfish (eastern Australia including eastern and western Tasmania) and a western stock (South Australia, GAB and Western Australia). Mitochondrial DNA (mtDNA) data showed differences following the same pattern as previous data, but suggested a much stronger division between the two stocks. Both data sets suggested there were no genetic differences between eastern Australia and New Zealand. However, it was unclear whether these findings were confounded due to scientific design (i.e sample size).
This project was initiated through GABRAG to address these stock structure issues and was a collaboration between the Australian Bureau of Agricultural and Resource Economics and Sciences (Andy Moore) and the Molecular Fisheries Laboratory at the University of Queensland (Jenny Ovenden, Carlos Bustamante and Andy Moore). The expectation was that this study would confirm the distinction between the eastern and western stocks, particularly as the classes of genetic markers used for this study mirrored those used previously.
The objectives of this project were to:
1) Improve understanding of stock structure for Western Gemfish west of Bass Strait;
2) Improve understanding of spawning locations for western Gemfish west of Bass Strait; and
3) Provide the Australian Fisheries Management Authority with recommendations on stock structure and boundaries on the basis of this evidence.
Fish were sampled from the mid-western Great Australian Bight (GAB), from two locations off the southwestern Victorian coastline at Kangaroo Island, (KI) and Portland (Por), from one location in western Bass Strait (WBS) and from one location off the coast of western Tasmania (WT).
To provide genetic comparisons among these target populations, fish were also sampled from the east coast of Tasmania (ET), the eastern coast of New South Wales (NSW) as well as New Zealand (NZ).
Previous research had found large genetic differences between eastern and western populations. However there was large sample size variation between both locations and it was unclear if the genetic differences were the result of biological processes or a sampling artefact. Archived historical samples from this study were obtained from the Australian Museum to confirm the previous results and to test for temporal stability of genetic patterns.
This study confirmed that there are two distinct stocks of Gemfish in Australia, with western Bass Strait the boundary between both stocks. The level of differentiation between the stocks for all genetic markers was high. This, along with the largely fixed mitochondrial haplotype differences between populations indicated minimal gene flow between stocks. This level of genetic structuring for a migratory marine finfish species with planktonic larval dispersal and contiguous distribution is very rare. For fisheries management purposes Gemfish to the east and west of Bass Strait can be managed as separate management units.
Immigrant Gemfish were found in both east and west stocks. These immigrants were classified as hybrids as they had the nuclear DNA from one stock and the mitochondrial from the other. However, if full hybridisation is occurring the introgression of genetic material between stocks would lead to the breakdown of stock boundaries. The levels of genetic subdivision between stocks detected in this study indicates that this is not occurring.
The study also found evidence for a smaller genetic effective population sizes in eastern Gemfish than western Gemfish. The results are preliminary but warrant further investigation as they may provide insight into why the eastern Gemfish population is not recovering from its overfished state.
This research has delineated two stocks of Gemfish in Australia and defined the boundary between both stocks. These data are very useful for assigning data for the stock assessment and for changing the management boundary between both stocks.
The report recommends that both eastern and western Gemfish stocks be treated as separate management units and the management boundary between both stocks be moved to a more appropriate location to better reflect both genetically distinct populations. The report also recommends further investigating the small effective population size found for eastern Gemfish.
Development of robust assessment methods and harvest strategies for spatially complex, multi-jurisdictional toothfish fisheries in the Southern Ocean
Assessment of the impacts of seal populations on the seafood industry in South Australia
The last 25 years have seen a 3.5 fold increase in the population size of New Zealand fur seals (NZFS) in SA, which now number over 85,000 individuals. This recovery may continue for a further 15-30 years, and the level at which populations may stabilise is unknown. New haul-out sites and breeding colonies are establishing across the State, some in close proximity to finfish aquaculture, and major commercial and recreational fishing areas. In addition, an Australian fur seal population has recently established in SA and has more than doubled in the last five years. There is also growing concern from the seafood and ecotourism (little penguins, giant cuttlefish) industries and the community that fur seals are overabundant and that their populations and impacts need to be managed. As a consequence of this broad industry and public concern, this project was listed as one of the priority areas for investment by the SAFRAB.
Most of the seals that interact with fisheries, aquaculture and ecotourism are juvenile and sub-adult males that restrict their feeding the shelf waters; however the diet and foraging behaviour of this part of the population is poorly understood. Little is also understood about the potential competitive interactions between the three species of seals that may be limiting the recovery of the threatened Australian sea lion. The project aims to investigate the diets and foraging distributions of seals in SA’s gulf and shelf waters to assess the importance of commercial fish and finfish aquaculture species in their diet. Trophic modelling will be used to assess the impact of consumption on current and future seafood production, and industry questionnaires and consultation will be used to assess the economic impact and the degree and nature of interactions between seals and finfish aquaculture, fisheries and marine ecotourism industries.
Final report
Shark Futures: A report card for Australia's sharks and rays
With growing concerns for the status of shark and ray populations world-wide, and increasing pressure to ensure Australia’s 320 species are effectively managed and conserved, there is a need for decision makers in government to have access to comprehensive and accurate information. One of the greatest challenges for the sharks and rays is that more than any other taxa they exist across the spectrum of interests from sustainable fisheries resources to threatened species requiring conservation. Further complicating the assessment and management of these species is the fact that many species ranges extend beyond Australia’s territorial waters, where management is implemented differently and populations may be in very different states. Australia’s abilities both in management of its sharks and rays, and the science that underpins it, are recognised as world-leading. Despite this there remain many challenges that face our sharks and rays, but they may not always be those that are faced by other nations in our region. Currently the available information is fragmentary and difficult to access, and most assessment is focused on only a few species targeted by fisheries. The growing information needs of initiatives such as Shark-Plan 2, CITES, CMS, ESD, WTO and EPBC listing struggle to be met because of the lack of a synthesis of information across this group. Locally relevant information on the status of sharks and rays, and the synthesis of knowledge about them, will thus be critical to addressing the challenges that face this group in Australian waters.
Final report
Project products
Movement, habitat utilisation and population status of the endangered Maugean skate and implications for fishing and aquaculture operations in Macquarie Harbour
Little is known about the life history of the endangered Maugean skate but it does appear to have a very restricted distributional range (Macquarie and Bathurst Harbours, the latter a marine protected area) and in all likelihood a small population size.
The expansion of marine farming in Macquarie Harbour represents a key element of the salmonid industry’s plan to significantly increase Atlantic salmon and rainbow trout production in Tasmania. In considering the planning application, the MFPRP identified that research is required to more properly understand the ecological effects of the proposed farming operations, including potential impacts on the Maugean skate. Key research priorities identified by the MFPRP were the need to describe distribution, abundance and general ecology of the species, such information being a precursor to determining the nature of interactions with marine farming operations. Furthermore, the Panel noted the need to better understand the potential effects on the Maugean skate of efforts to recover escapees through fish-down using gillnets. This concern links to the more general population risk posed by gillnetting, noting that skate are taken incidentally in commercial and recreational gillnets and that gillnetting activity is strongly associated with targeting of escapees.
By employing acoustic tracking and non-destructive biological sampling techniques, this project will provide the science to understand the nature of interactions between fishing and aquaculture activities and the Maugean skate as well as enhancing our knowledge about its conservation status. Through such understanding it will be possible to evaluate risk and develop strategies to manage interactions and, where necessary, implement measures to mitigate negative impacts on the skate.
This proposal addresses RD&E priorities relevant to understanding the impacts of aquaculture due to expansion as well as mitigating the impacts of fishing on threatened, endangered and protected species.
Final report
The impact of habitat loss and rehabilitation on recruitment to the NSW eastern king prawn fishery
This project addresses the 2013 NSW FRAB research priority “Understanding environmental impacts on commercially important species”. The paucity of knowledge of EKP nursery habitats in NSW is a significant problem, as the estuarine nursery phase is the period where EKP are most likely to be affected by (non-fishing) anthropogenic activities and potentially represents a recruitment bottleneck which directly affects productivity. Investment in research in the southern United States has found that:
1) There is quantitative relationship between intertidal vegetation and the yield of penaeid prawns (Turner, 1977);
2) Restoration of connectivity and rehabilitation of saltmarsh areas has a quantifiable benefit for prawn fisheries (Rozas et al., 2005).
Research into estuarine nursery habitats for EKP in south-eastern Queensland forms the basis of the sustainable management of their prawn fishery through a recruitment index. In NSW, however, there is a paucity of knowledge on the early life history stages, including recruitment to estuaries, use of estuarine habitats by natural recruits, and factors that affect growth and survival of young EKP. Regulating river flows in estuaries and restricting tidal flow into wetlands can destroy connectivity between new recruits and their nursery areas. NSW commercial fishers have indicated that wetlands in the lower portion of estuaries (such as Hexham Swamp in the Hunter River) were historically significant nursery areas for EKP, prior to their destruction. These anecdotes highlight a need to understand the nursery habitats and hydrographic conditions that contribute to the EKP fishery in NSW. An understanding of the nursery function of these areas, the extent of habitats lost, remaining and restored, is required to provide a basis for assessing the competing costs and benefits of habitat rehabilitation. Further, this project represents an important case study to highlight the potential financial benefits to fisheries of rehabilitation and restoration of appropriate estuarine habitats.