Australian Sea Lion

Neophoca cinerea

The Australian sea lion is the only pinniped endemic to Australian waters, and one of the rarest sea lion species in the world (1) with a population of only 11,000 individuals (2 in 3).  Australian sea lions are long-lived and late to mature like other pinnipeds, but also possess a unique asynchronous reproductive cycle (4 in 1) of about 17.6 months, the cause of which remains unknown (5).  Females also display such extreme natal site fidelity that breeding colonies are genetically distinct (1,6) and face a higher risk of localized extinction (7). Australian sea lions were hunted from the 18th century into the 20th century, and are now extinct along Australia’s southeastern coast (1). Although the species’ pre-exploitation population size and range are not well understood, it is believed that they have not recovered as quickly as Australia’s other pinniped species. (6). Australian sea lions are listed as threatened under the Environment Protection and Biodiversity Conservation Act (1999) of the Australian Commonwealth.

The same population characteristics that have contributed to the Australian sea lion’s limited recovery leave many of the species’ subpopulations vulnerable to bycatch-related mortality (6,8).  Australian sea lions interact most frequently with the demersal gillnet and southern and western rock lobster fisheries (8).  Commercial and recreational rock lobster traps pose a particular threat to juvenile sea lions (4 in 8, 7), which may become trapped and drown while attempting to steal lobsters or bait.  Between two and six mortalities were reported annually from 2000-2004 in the Western Australia rock lobster fishery (7), but the impact of this fishery on sea lion populations is unknown (1).

Monofilament gillnets used in Australia’s shark fishery are a more significant bycatch concern because the fishery occurs year-round, overlaps with foraging grounds and affects all age classes (8).  Although gillnets are the most commonly identified cause of entanglement (9 in 6), other fishing-related marine debris, including packing tape and rope, fish lines and hooks, and baitbox straps, are an entanglement risk as well (3,6).  Australian sea lions suffer the third-highest entanglement rate, estimated at 1.3%,  of any pinniped species (3,8).  This translates to approximately 146 incidents and 64 deaths annually (3), though interactions may go unreported or unobserved (6).  Australian sea lions also may come into contact with predator exclusion nets used in the aquaculture industry (6).

The Australian government manages bycatch issues at the state, territory, and  national levels.  The National Policy on Fisheries Bycatch coordinates bycatch mitigation efforts for fisheries in state and territorial fisheries, while the Commonwealth Policy on Fisheries Bycatch addresses bycatch in commonwealth fisheries.  Under the Commonwealth Policy, fishery-specific Bycatch Action Plans have been developed specifically to manage bycatch interactions with species, including the Australian sea lion, which have no commercial value or cannot be retained, and may suffer from unseen interactions fishing gear.  A lack of quantitative bycatch data makes it difficult to assess the effects of incidental capture on subpopulations (8), and consequently to develop a targeted mitigation strategy.  Sea lion exclusion devices (SLEDs) can be an effective way to prevent sea lions from gaining access to lobster pots.  Several different types have been developed, including a steel bar that fits across the neck of the trap and a T-shaped bar that sits perpendicular to the seafloor (7).  In the demersal gillnet fishery, spatial management strategies, such as closures, may be a way to divert fishing effort away from high-risk subpopulations (8).  

References and Additional Resources:

1.  Campbell, R. 2005b. Historical distribution and abundance of the Australian sea lion (Neophoca cinerea) on the west coast of Western Australia. Fisheries Research Report No.148. Government of Western Australia, Department of Fisheries. 44p. Available at www.fish.wa.gov.au/docs/frr/frr148/frr148.pdf

2.  Goldsworthy, S.D., Bulman, C., He, X., Larcombe, J., and C. Littnan. 2002. Trophic interactions between marine mammals and Australian fisheries: an ecosystem approach. In: Gales, N., Hindell, M., and R. Kirkwood, eds., Marine mammals and humans: towards a sustainable balance. CSIRO Publishing, Melbourne

3.  Page, B., McKenzie, J., McIntosh, R., Baylis, A., Morrissey, A., Calvert, N., Haase, T., Berris, M., Dowie, D., Shaughnessy, P.D., and S.D. Goldsworthy. 2004. Entanglement of Australian sea lions and New Zealand fur seals in lost fishing gear and other marine debris before and after Government and industry attempts to reduce the problem. Marine Pollution Bulletin 49: 33-42

4.  Gales, N.J., Shaughnessy, P.D., and T.E. Dennis. 1994. Distribution, abundance and breeding cycle of the Australian sea lion Neophoca cinerea (Mammalia: Pinnipedia). Journal of Zoology, London 234: 353-370

5.  Higgins, L.V. 1993. The nonannual, nonseasonal breeding cycle of the Australian sea lion, Neophoca cinerea. Journal of Mammalogy 7(2): 270-274

6.  McKenzie, J., Goldsworthy, S.D., Shaughnessy, P.D., and R. McIntosh. 2005. Understanding the impediments to the growth of Australian sea lion populations. Final report to the Department of the Environment and Heritage, Migratory and Marine Species Section. 112p. Available at www.sardi.sa.gov.au/pdfserve/fisheries/pub/pelag_eco/rd04_0171.pdf

7.  Campbell, R. 2005. Report for the Sea Lion Scientific Reference Group. Fisheries Occasional Paper No. 16. Government of Western Australia, Department of Fisheries. 31p. Available at www.fish.wa.gov.au/docs/op/op016/fop016.pdf

8.  Goldsworthy, S.D., and B. Page. 2007. A risk-assessment approach to evaluating the significance of seal bycatch in two Australian fisheries. Biological Conservation 139: 269-285

9.  Shaughnessy, P. and T. Dennis. 2001. Research on New Zealand fur seals and Australian sea lions in South Australia, 2000-2001 . Report to South Australian National Parks and Wildlife Service.