MISA - Marine Innovation SA

• Seafood Product Quality & Value-adding
• Aquaculture Innovation
• Ecosystem Services
• Biosecurity

Assessment of the implications of interactions between fur seals and sea lions and the southern rock lobster and gillnet sector of the Southern and Eastern Scalefish and Shark Fishery (SESSF) in South Australia

Outcomes Achieved to Date

This report provides the most comprehensive appraisal of the risk posed by bycatch to subpopulations of Australian sea lions and New Zealand fur seals, by the SA rock lobster and gillnet sector SESSF fisheries. Further it has identified the research required to ensure that SA rock lobster and the gillnet sector SESSF fisheries are managed according to ESD principles, and that interactions with seals are measured, assessed and mitigated. Adoption of these recommendations will lead to the development and adoption by industry and management of mitigation options to reduce seal bycatch. This will ensure that outstanding ESD recommendations detailed in fishery ESD assessments and the mitigation of the key threatening process identified in the Australian sea lion Draft Recovery Plan are addressed, leading to the recovery and potential future delisting of the species.

Non-Technical Summary

Recent Commonwealth Department of the Environment and the Heritage (DEH) Ecological Sustainable Development (ESD) assessments of the South Australian (SA) rock lobster (SARLF) and southern and eastern scalefish and shark fishery (SESSF) identified interactions with protected species (particularly seals), as one of the key bycatch issues. The issues are most relevant to SA waters where the majority of Australia’s New Zealand fur seal(NZFS) and endemic and threatened Australian sea lion (ASL) populations are located, and where un-quantified interactions between seals and the SARLF and gillnet sector of the SESSF fisheries are known to occur. Recommendations from fishery ESD assessments, fishery Bycatch Action Plans, and a recently drafted Recovery Plan for the ASL, have all identified the importance of assessing and mitigating interactions between seals and commercial fisheries. This study provides a desk-top risk-assessment of seal fisheries interactions in the SARLF and gillnet sector SESSF in SA and adjacent waters, and makes recommendations on future research and management responses. A review of the PIRSA and AFMA fishery logbooks identified the major constraint to the assessment of bycatch risk to seal subpopulations was the absence of quantitative data on bycatch rates in both the gillnet sector SESSF and SARLF. Anecdotal evidence and entanglement data suggest there has been significant underreporting of seal interactions in these fisheries.

In SA there are 38 ASL subpopulations that produce around 2,674 pups, with the total population size estimated at about 10,900. However, most pup production (67%) occurs at 6 sites, hence the median pup production is very low (25.5 pups), with the majority of sites producing small numbers of pups (60% produce <30 pups per season). Not surprisingly, population viability analysis (PVA) on ASL subpopulations reinforced the recent listing of the ASL as a threatened species, by confirming that large numbers of subpopulations with low pup production are vulnerable to extinction. PVA simulations suggested that in absence of anthropogenic mortality, a number of ASL subpopulations will go quasi-extinct (<10 females), but in the face of small (1-2 additional females/year) but sustained anthropogenic mortality (eg. from fishery bycatch), most other small subpopulations will become quasi-extinct and negative growth will become a feature of even the largest subpopulations. There is apparent depletion (i.e. very low pup production) of a large number of subpopulations that may be indicative of widespread subpopulation declines in the species. That such declines may be ongoing and attributable to anthropogenic mortality (ie. fishery bycatch) is a hypothesis that requires urgent attention.

In contrast to ASL, there are relatively few NZFS subpopulations (13) in SA, but the total pup production is considerably greater (17,622), with an estimated total population size of around 83,800. Populations are increasing, and PVA identified that most subpopulations were not-threatened. The risk of bycatch to both seal species in the gillnet SESSF and SARLF were assessed based on estimates of interaction probabilities. These were a function of the extent to which historic fishing effort and seal foraging effort (based on foraging distribution and population models) overlap in space and time. ASL demonstrated the highest risk of significant depletion and quasi-extinction as a result of fishery bycatch. In contrast, the risk to NZFS subpopulations is very low. By combining PVA outcomes with bycatch scenarios based on interaction probabilities, this study identified the subpopulations, regions and marine fishing areas (MFAs) most at-risk from seal bycatch. Bycatch from the gillnet SESSF is most likely to provide the greatest risk to ASL, because of almost complete spatial overlap in fishing effort with ASL foraging effort, it is a year-round fishery with relatively high fishing effort that can potentially target all ASL age-classes. The impact from SA RLF is likely to be less because there is less overlap in fishing effort with ASL foraging effort, fishing is restricted to seven months of the year (November-May), and bycatch is likely to be restricted to pups and juvenile seals. However, the potential additive and interactive impacts posed by combined bycatch in these fisheries could be significant, especially for ASL.

Results from this study suggest the two fisheries investigated lend themselves to different mitigation approaches to addressing seal bycatch issues. In the gillnet SESSF, gear modification options are limited, but spatial management of fishing effort may provide a range of risk-reduction options to management, but would need to be coupled with independent observer bycatch data to demonstrate and justify the benefits from different closure options. In contrast, there are significant options for gear modification in the SARLF, with pot protection devices already used in some parts of the fishery. Quantitative testing of these and alternate protection measures (as is taking place in the WA WRLF), and industry wide adoption of best-mitigation practices may eliminate seal bycatch in this fishery, without the need for an expansive and costly independent observer program. Recommendations for future research are made, that should result in the successful mitigation of seal bycatch issues, and as a consequence address the recommendations of the fishery ESD, Bycatch Action Plan, ASL Recovery Plan and assist in the recovery of the threatened ASL.