The 2018 Commonwealth Fisheries Bycatch Policy (Bycatch Policy) establishes the requirement for bycatch management in Commonwealth-managed fisheries. The Guidelines for the Implementation of the Commonwealth Fisheries Bycatch Policy aim to provide assistance to Australian Government entities (principally the Australian Fisheries Management Authority (AFMA) but also bodies (industry or otherwise) that AFMA outsources to, including industry-based co-management arrangements) in interpreting and implementing the requirements of the Bycatch Policy.

Bycatch is defined as a species that is either incidentally taken in a fishery and returned to the sea, or incidentally killed or injured as a result of interacting with fishing equipment in the fishery, but not taken. The Bycatch Policy distinguishes between two classes of bycatch—general bycatch and Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) listed species. General bycatch are species that are not listed under the EPBC Act. EPBC Act–listed species are managed in parallel and, where feasible, jointly with general bycatch. However, these species are principally managed under Australia’s national environment legislation—the EPBC Act. Specific guidance for managing EPBC Act–listed species is provided separately by the Department  of the Environment and Energy. These guidelines do not aim to alter or influence  that management. These guidelines are for general bycatch species only and not  EPBC Act–listed species.

1.1 Relationship with the Harvest Strategy Policy: These guidelines operate in parallel with the Commonwealth Fisheries Harvest Strategy Policy (Harvest Strategy Policy) and the Guidelines for Implementation of the Commonwealth Fisheries Harvest Strategy Policy (Harvest Strategy Policy Guidelines) and support AFMA’s approach to fisheries planning and documentation. AFMA has recently revised its approach to planning and documenting the management of Commonwealth fisheries. AFMA has commenced the development of a Fisheries Management Strategy (FMS) for each of its Commonwealth fisheries to combine management of commercial species (under a harvest strategy), non-commercial species (under a bycatch strategy), habitats and communities, research, and data and monitoring into a single integrated document for each of its fisheries. This single strategy approach aims to provide greater consistency, clarity, transparency and cost efficiency in how AFMA develops, documents and implements its management processes. It also aims to ensure better linkages between these components.

These guidelines are designed to assist AFMA deliver against the requirements of the Bycatch Policy and assist in developing the bycatch chapter of the FMS for each Commonwealth fishery. Where appropriate, examples are provided to illustrate key points that address specific fisheries management challenges.

1.2 Intent of the Bycatch Policy Guidelines: The Bycatch Policy advocates a risk-based approach to assessing and managing general bycatch. These guidelines provide information to assist AFMA in operationalising this approach. They encourage innovation and adoption of global best practice where appropriate. They also promote a balance between the risks to bycatch and the consequences of additional management on the fishery. Where the risks of negative impacts from fishing on bycatch are low, management responses are expected to prioritise innovation to minimise interactions without unnecessary restriction on commercial operations. Conversely, where the risks are high, greater prescription may be required to reduce the risks to bycatch (that is, to medium or low risk through appropriate management responses) in addition to promoting innovative solutions. This approach is consistent with the principles of risk–cost–catch applied to the development of harvest strategies for commercial stocks. The guidelines assist AFMA with recognising information uncertainty and incorporate it into its assessment of risk and application of the precautionary principle.

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.