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Endangered Species Research

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ESR 14:203-216 (2011)  -  DOI:

Assessing the effectiveness of the Great Australian Bight Marine Park in protecting the endangered Australian sea lion Neophoca cinerea from bycatch mortality in shark gillnets

D. J. Hamer1,2,*, T. M. Ward2,3, P. D. Shaughnessy4, S. R. Clark

1Australian Marine Mammal Centre, Australian Antarctic Division, 203 Channel Highway, Kingston, Tasmania 7050, Australia
2University of Adelaide, North Terrace, Adelaide, South Australia 5000, Australia
3South Australian Research and Development Institute - Aquatic Sciences, 2 Hamra Avenue, West Beach, South Australia 5024, Australia
4South Australian Museum, North Terrace, Adelaide, South Australia 5000, Australia
5Department for Environment and Heritage, Liverpool Street, Port Lincoln, South Australia 5606, Australia

ABSTRACT: The Endangered Australian sea lion Neophoca cinerea occurs in low numbers, exhibits low fecundity, extreme philopatry and substantial population genetic structure at the breeding colony level. These traits may increase susceptibility to population decline, with additional mortality as bycatch in shark gillnets being a possible threat. The Great Australian Bight Marine Park (GABMP) was established, in part, to protect the small and remote Bunda Cliffs population from anthropogenic impacts such as commercial fishing. This study investigated the effectiveness of the GABMP in reducing spatial overlap between Australian sea lions and gillnets and in preventing bycatch. An independent fishery observer program reported a mortality rate of 0.0206 individuals (ind.) km–1 of gillnet set within the GABMP, amounting to between 4 and 15 (confidence bounds of standard error of the estimate) ind. killed there during the most recent breeding cycle. A mortality rate of 0.0093 ind. km–1 of gillnet set was recorded across the broader GAB region, amounting to between 14 and 33 ind. killed each breeding cycle during recent times, and between 128 and 177 over the 10 yr since the GABMP was established in the mid-1990s. These reported bycatch levels are unlikely to be sustainable and may represent minimum estimates, because drowned individuals may drop out of the gillnet and go unobserved. A tracking program involving 9 females (5.6% of the estimated female population) demonstrated that they spent only 27.7% of their time inside the GABMP. Four of them regularly travelled more than 180 km from home, or 9 times further than the southern boundary of the GABMP. These results indicate that the level of protection afforded by the GABMP to Australian sea lions residing at Bunda Cliffs is unlikely to reduce ­bycatch to below the levels that would reduce the risk of decline in this small population. Suggested ­improvements to the GABMP include a year-round closure to gillnetting, low bycatch limits and extension of the southern boundary further south. Additional regulatory mechanisms may be needed in the gillnet fishery to minimise its impact on this and other small Australian sea lion populations.

KEY WORDS: Pinniped · Australian sea lion · Endangered · Demersal gillnet · Operational ­interaction · Bycatch mortality · Foraging behaviour · Marine protected area

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Cite this article as: Hamer DJ, Ward TM, Shaughnessy PD, Clark SR (2011) Assessing the effectiveness of the Great Australian Bight Marine Park in protecting the endangered Australian sea lion Neophoca cinerea from bycatch mortality in shark gillnets. Endang Species Res 14:203-216.

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