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Leading the way in gillnet bycatch mitigation research

The international Marine Mammal – Gillnet Bycatch Mitigation Workshop, recently held in Woods Hole, Massachussets, USA tackled fisheries bycatch - one of the biggest threats to many marine mammals worldwide. The workshop brought together experts in this field to assess gillnet bycatch mitigation techniques and develop recommendations regarding best practices, including identifying future research priorities.

A/Prof Simon Goldsworthy, South Australian Research and Development Institute (SARDI), presented on the impact and mitigation of Australian sea lion bycatch using spatial closures in the shark gillnet fishery off South Australia. Australian Sea Lions (Neophoca cinerea) (ASL) are a threatened species endemic to southern Australia, and subject to incidental mortality (bycatch) in demersal gillnet shark fisheries. Bycatch has been identified as the key threatening factor for the species, and recently fishery closures have been introduced to mitigate bycatch impacts.

Moving beyond the fishery observer data typically used, SARDI researchers used data from four main sources: i) satellite tracking data to estimate distribution of foraging effort; ii) survey data on ASL subpopulations size; iii) data from a dedicated bycatch observer program; and iv) detailed spatial data on the distribution of fishing effort, to model and assess the risks to ASL populations posed by the shark gillnet fishery.

Satellite telemetry data from 210 individual ASL (157 females, 31 adult males, 22 juveniles), from 17 subpopulations, in conjunction with depth and distance from colony data, were used to develop statistical models of the distribution of foraging effort across the population of ASL. Bycatch mortality rates based on observer data were highly correlated with sea lion foraging density, enabling levels of bycatch mortality that would result from different distributions and levels of fishing effort to be estimated with confidence limits. This approach was used to estimate the impacts the current fishery is having on populations of ASL, and provide closure options required to mitigate bycatch threats to ASL populations.

The rigorous nature of the quantitative data used to assess the impact of the shark gillnet fishery on ASL and model different management scenarios was recognised by the international audience as being at the forefront of gillnet bycatch mitigation research.

Visit the International Marine Mammal - Gillnet Bycatch Mitigation Workshop website for abstracts and further information.