Australian Sea-lion (Neophoca cinerea)

Advice to the Minister for the Environment and Heritage from the Threatened Species Scientific Committee (TSSC) on Amendments to the list of Threatened Species under the Environment Protection and Biodiversity Conservation Act 1999 (EPBCAct)
14 February 2005

1. Scientific name, common name (where appropriate), major taxon group.

Neophoca cinerea (Australian Sea-lion)

2. Description

The Australian Sea-lion is Australia's only endemic and least numerous seal species. It belongs to the Otariidae family, which includes all seals with ear flaps and seals which can propel themselves through the water using their front flippers. They are more agile on land than 'true' seals, as they are capable of walking on all four flippers.

Male Australian Sea-lions are between 200-250 cm long, weigh 250-300kg and are dark blackish brown with a mane of long coarse hairs. Females are 130-180cm long, weigh 70-100kg and are silvery grey in colour on their backs and creamy yellow fading to brown on their bellies. Pups are 62-68 cm long at birth, weigh 6.4-7.9 kg and are chocolate brown with a pale fawn crown until they moult at two months to a juvenile coat similar to an adult female.

The Australian Sea-lion is unique among pinnipeds (seals, sea-lions and walruses) in that it has a non-annual breeding cycle that is asynchronous across the breeding colonies, meaning that the different colonies do not breed at the same time. The species' gestation period of up to 14 months is the longest of any pinniped, it has a protracted breeding period of 4-7 months from the birth of the first pup to the birth of the last pup of the season, a long lactation period of 17.5 months and the females show extreme levels of natal site fidelity, only breeding at the site they were individually born at.

3. National context

The Australian Sea-lion is endemic to Australia. Its breeding range extends from the Houtman Abrolhos Islands in Western Australia to The Pages Islands that lie east of Kangaroo Island in South Australia. The population is estimated to be 11,200 individuals, spread among 67 breeding colonies. Thirty per cent of the population is found in Western Australia and 70% occurs in South Australia. An estimated 40% of the population is found in the three largest colonies located at the eastern end of its range. These large colonies are found at The Pages Islands with approximately 2100 individuals and 474 pups per season, Dangerous Reef with approximately 1650 individuals and 351 pups per season, and Seal Bay at Kangaroo Island with 700 individuals and 160 pups per season. These three large colonies all occur in eastern South Australia. The smaller colonies do not have complete population estimates, but the average pup count per season is 29 pups, ranging from 120 pups to 1 pup for the smaller colonies. Based on colonies with complete population estimates, a smaller colony with 29 pups would contain approximately 114 individuals.

The Australian Sea-lion is listed as rare under the South Australian National Parks and Wildlife Act 1972 and is listed as specially protected under the Western Australian Wildlife Conservation (Specially Protected Fauna) Notice 2003.

EPBC Act criteria.

The TSSC judges the species is eligible for listing as vulnerable under the EPBC Act. The justification against the criteria is as follows:

Criterion 1 - It has undergone, is suspected to have undergone or is likely to undergo in the immediate future a substantial reduction in numbers.

The population of the Australian Sea-lion is estimated to be 11,200. The range and abundance of the species has contracted following harvesting of Australian Sea-lions by European sealers in the eighteenth and nineteenth centuries. Prior to seal harvesting, the species inhabited much of Bass Strait but breeding colonies have now disappeared from this eastern part of its range.

There is no data on the pristine abundance of the population, ie, prior to harvesting in the eighteenth and nineteenth centuries, however the numbers of Australian Sea-lion pelts harvested indicate that the population underwent a significant historic decline in the early 1800s. In Western Australia, approximately 3000 pelts were harvested from the islands of the Recherche Archipelago, a cluster of islands offshore of Esperance, which is similar to the current population estimate for the entire southern Western Australian coast. There is a high probability that the numbers of finished pelts is an underestimate of the total cull.

Estimates of pup production are the most accurate method currently available to assess the abundance of Australian Sea-lions. However, estimating pup production over the complete range of the species is problematic and estimates contain a high level of uncertainty. This is due to a combination of factors, particularly the unusual life history characteristics of the species that makes it difficult to study. Some of these factors include the high and variable pup mortality rate during the pupping season and the 4-7 month protracted pupping season, where the first pups of the season have left the colony before the last are born, meaning that not all pups born in the same season are simultaneously present for counting.

Despite the difficulties of detecting population trends in the Australian Sea-lion, declines of 25% in pup production were observed at four of the smaller southern Western Australian colonies over the last ten years. In addition, a colony on the west coast of South Australia was observed to decline from 23 pups in the 1990 season to only one pup four seasons later in 1995/96. The three large colonies in eastern South Australia appear to have been relatively stable over the last decade. However, recent unpublished raw data on pup counts over the last 13 years at the large Seal Bay colony suggest that there may be some decline, although there is insufficient data to determine the level of this decline.

Failure of the Australian Sea-lion population to recover from European seal harvesting

The failure of the Australian Sea-lion population to recover from the historic threat of European seal harvesting at the same rate as the Australian and New Zealand Fur Seals is cause for concern. Some of the life history characteristics of the Australian Sea-lion naturally hinder the recovery capability of the species, such as their reproductive output being limited to approximately one pup every 17.5 months, compared to one pup annually for the other two species. The protracted pupping season of 4-7 months is a period of high risk for young pups due to the aggressive behaviour of reproductive males. Pup mortality during their first 5 months is extremely high and up to 45% in some large colonies. By contrast, pup mortality in fur seals is less, due to shorter pupping seasons and less aggressive male behaviour. A further characteristic that has inhibited the recovery of the Australian Sea-lion is that as a sea-floor forager, it is limited to coastal shelf waters, whereas the fur seals have less constrained foraging behaviour and can exploit both mid-water and sea-floor environments.

In addition to these life history characteristics, the failure of the Australian Sea-lion population to recover from European seal harvesting has been attributed to interactions with humans. With its foraging restricted to sea-floor coastal environments, the Australian Sea-lion has a high exposure to human activities, particularly gillnet and cray pot fisheries, where mortalities caused by interactions with these fisheries have been documented. In addition, the breeding colonies on islands near centres of human activity are also the sites most accessible for humans to land on. Australian Sea-lions are therefore more vulnerable to displacement and disturbance at these sites than fur seals, which breed at less accessible sites.

There is limited data available on overall levels of mortality of Australian Sea-lions caused by interactions with human influences, although it is expected to be low. However, the loss of even a few reproductive or potentially reproductive individuals represents a threat to the viability of small colonies. Most Australian Sea-lion colonies are small and as the species shows extremely limited, to non-existent, capacity to recolonise depleted areas, even low levels of additional mortality could have a significant effect on the conservation status of the population as a whole.

Reduction in numbers caused by interactions with fisheries and entanglement with marine debris

The major threat identified for the Australian Sea-lion is interactions with fisheries, particularly shark and crayfish fisheries. The monofilament gill net used in shark fisheries is the entangling material observed in 55% of Australian Sea-lion entanglements. Sea-lions have been also observed to forage in crayfish and lobster pots, occasionally becoming trapped and drowning. Entanglements and drowning of Australian Sea-lions have also been associated with aquaculture operations. Australian Sea-lion carcasses have been discovered with gun shot wounds near known fisheries and aquaculture sites.

There is little data available on the overall levels of Australian Sea-lion mortality caused by interactions with fisheries, but the rate of entanglement with marine debris, including fishing gear, is estimated to be in the order of 146 individuals per year, with at least 64 of these dying as a result of the entanglement. These entanglements represent 1.3% of the Australian Sea-lion population, which is the third highest rate of entanglement for a pinniped species world wide. These estimates are based on observed entanglements and are considered to be very conservative. The actual number of Australian Sea-lions that die at sea as a result of entanglement is believed to be much higher but has not been quantified, because the animals are beyond observer range and therefore not counted (Page et al 2004).

Entanglement of Australian Sea-lions in rock lobster fisheries has reduced with the recent introduction of effective seal exclusion devices. However, juveniles of the species are still entangled regularly in crab pots without seal exclusion devices and most frequently in monofilament netting used in shark gillnet fisheries (Page et al 2004).

Possible reduction in numbers caused by pollution

Several studies have shown that marine mammals in the Southern Hemisphere are carrying higher pollutant loads of organochlorines and heavy metals than would be expected naturally, due to pollution of the ocean and the food chain by anthropogenic substances. High trophic level predators, such as seals and sea-lions, are particularly susceptible. However, specific data on pollutant loading in the Australian Sea-lion is not available. The possible impact is also hard to predict, although there is general agreement that these pollutants are detrimental and may specifically affect certain body systems and functions. These include the immune, endocrine and nervous systems of pinnipeds, resulting in disruption in growth, development, reproductive ability and resistance to disease (Evans 2003, Evans et al 2004).

Reduction in numbers caused by competition with fur-seals

The increasing abundance of Australian and New Zealand Fur-seals as these species recover from European seal harvesting has been identified as a possible source of competition with the Australian Sea-lion. The distribution of the New Zealand Fur-seal overlaps with that of the Australian Sea-lion and the two species have similar foraging, breeding and haul-out ranges. However, the terrestrial habitat preferred by each species is substantially different, with each species generally choosing distinctly different sites even when they occur on the same islands.

There is currently no overlap in the terrestrial range of the Australian Sea-lion and the Australian Fur-seal, although the Australian Fur-seal is expanding its range and may breed within the Australian Sea-lion's range in the future. However, while both the Australian Sea-lion and the Australian Fur-seal are primarily sea-floor feeders, the potential for trophic competition is theoretically low, as both have a diverse diet. In addition, the two species have shared the same range in the past, ie prior to European seal harvesting when the Australian Sea-lion had breeding colonies in Bass Strait.

Therefore, the possibility of competition between the Australian Sea-lion and the Australian Fur-seal species is not considered to be a serious threat to the Australian Sea-lion. However, competition with the New Zealand Fur-seal may be having an effect on the recovery capability of the Australian Sea-lion, although this effect has not been fully identified or quantified.

Conclusion

The Australian Sea-lion population underwent a massive decrease in numbers caused by European harvesting. The population appears to have stabilised following the cessation of harvesting in 1825, although it has not recovered to its former abundance or range. Over the last ten years, decline in some of the smaller colonies has been observed and the population at the large Seal Bay colony may also be in decline. Mortality of individual Australian Sea-lions following interactions with fisheries and entanglement with marine debris has also been recorded and estimates indicate that the level of mortality is unsustainable for individual colonies. Competition for resources with the New Zealand Fur-seal may also be negatively effecting the Australian Sea-lion, although this remains to be investigated and quantified. While determining population trends in the Australian Sea-lion is difficult, the rates of mortality caused by interactions with humans and possible competition with New Zealand Fur-seals, combined with the Australian Sea-lion's naturally poor recovery abilities indicates that the species is likely to experience a further reduction in numbers.

Therefore, the species is eligible for listing as vulnerable under this criterion.

Criterion 2 -Its geographic distribution is precarious for the survival of the species and is limited.

The Australian Sea-lion experienced a decline in its area and extent of occupancy following European seal harvesting in the eighteenth and nineteenth centuries. Accounts from early explorers and seal harvesters indicate that the species inhabited much of Bass Strait but breeding populations have now disappeared from this eastern part of its range.

Historic records also point to several breeding colonies which appear to have been abandoned around Perth and Albany in Western Australia, leading to a fragmented national population.

The current contracted geographic distribution of the Australian Sea-lion is due to a lack of recolonisation into previously abandoned areas and the high level of female birth site specificity. Female Australian Sea-lions will only return to their own birth site to breed, meaning that the species has an extremely limited capacity for emigration. Localised depletion cannot be buffered by immigration from neighbouring colonies, therefore the extirpated range is unlikely to be recolonised. With female recruitment occurring solely from within each colony, the degree of genetic isolation between each colony is extremely high.

The combination of genetic isolation between colonies and the long breeding interval of this species leaves individual colonies vulnerable to localised depletions or extinctions caused by environmental or anthropogenic disturbance.

However, despite its fragmented distribution, the extent of occurrence of the Australian Sea-lion is large, ranging from the Houtman Abrolhos Islands in Western Australia to the Pages Islands in South Australia. Its area of occupancy is difficult to calculate as information on the foraging space of the species is poor. Expert estimates of area of occupancy vary widely but it cannot be established that its geographic distribution is precarious for the survival of the species or is limited.

Therefore, the species is not eligible for listing as vulnerable under this criterion.

Criterion 3 - The estimated total number of mature individuals is limited and evidence suggests that the number will continue to decline at a substantial rate.

The total population of Australian Sea-lions is estimated at 11,200. Taking into account the most recent estimates of annual pup production and numbers of juveniles and subadults, the population contains an estimated 7152 - 8174 mature individuals.

The Australian Sea-lion underwent a significant decrease in numbers following European harvesting in the 1800s. The failure of the Australian Sea-lion population to recover once harvesting pressure was removed, unlike the Australian and New Zealand Fur-seal, is of concern. The unusual life history characteristics that have evolved in the Australian Sea-lion, while not a threat in isolation, hinder the recovery capability of the species. The 17.5 month breeding cycle is disadvantageous, as pups are produced less frequently than other pinniped species, who reproduce annually. The species has a naturally high young pup mortality and is restricted in foraging to benthic coastal shelf waters. The extremely high female natal site fidelity (where females only return to the breeding colony of their own birth to reproduce) severely limits the capability of the species to recolonise previously inhabited colonies, so localised depletions are rarely recoverable.

In addition to the failure of the Australian Sea-lion population to recover in the absence of harvesting pressure, evidence suggests that some of the smaller colonies have declined by 25% over the last ten years.

One of the documented threats to the Australian Sea-lion is interaction with fisheries, particularly shark and crayfish fisheries. Sea-lions have been observed to forage in crayfish and lobster pots, occasionally becoming trapped and drowning, and have been known to become entangled in gillnets. As discussed under Criterion 1, an estimated 146 Australian Sea-lions become entangled in marine debris annually, with 64 individuals dying as a result. These estimates of entanglement related mortality are believed to be very conservative. Australian Sea-lion carcasses have also been discovered with gun shot wounds near known fisheries sites.

There is limited data available on overall levels of mortality of Australian Sea-lions caused by interactions with human influences, although it is expected to be low. However, the loss of even a few reproductive or potentially reproductive individuals represents a threat to the viability of small colonies. Most Australian Sea-lion colonies are small and as the species shows extremely limited to non-existent capacity to recolonise depleted areas, even low levels of additional mortality caused by interactions with human influences could have a significant effect on the conservation status of the population as a whole.

There are less than 10,000 mature individuals in the Australian Sea-lion population. Over the last ten years, decline in some of the smaller colonies has been observed and mortality of individual Australian Sea-lions following interactions with fisheries has also been recorded. The recent decline in the smaller colonies and the possible decline in pup production at the large Seal Bay colony is cause for concern and the mortality caused by fisheries interactions suggests that numbers may continue to decline at a substantial rate.

Therefore, the species is eligible for listing as vulnerable under this criterion.

Criterion 4 - The estimated total number of mature individuals is low.

While the Australian Sea-lion is regarded as one of the rarest pinniped species in the world, the population is still regarded as viable and there are more than 1000 mature individuals.

Therefore, the species is not eligible for listing as vulnerable under this criterion.

Criterion 5 - Probability of extinction in the wild

There is no quantitative data available against this criterion.

Therefore, the species is not eligible for listing as vulnerable under this criterion.

5. Conclusion

The Australian Sea-lion has experienced a decline in numbers and range following European seal harvesting. The population has not recovered even though large scale seal harvesting has not occurred for over 100 years, although it appears to have stabilised at post-harvest levels. This failure to recover is attributed to the species unusual life history characteristics, including the long inter-birth interval, high pup mortality, restricted foraging habitat and poor recolonisation and dispersal ability.

The Australian Sea-lion population is now at low numbers and several colonies have been observed to decline by a further 25% over the last ten years. The three large colonies in South Australia have been relatively stable over this time, although recent raw pup count data suggests that the large colony at Seal Bay is also now in decline. The low numbers, poor dispersal and genetically isolated structure of the species' breeding colonies renders it sensitive to environmental and anthropogenic disturbance. One of the threats identified for the species is interactions with fisheries and entanglement with marine debris. While only limited data on the extent of mortality caused by fisheries interactions and entanglement with marine debris is available, it is known to occur across the range of the Australian Sea-lion.

The failure of the Australian Sea-lion population to recover from harvesting, the decline in some of the smaller colonies and the loss of individuals through interactions with fisheries and entanglement with marine debris is cause for concern. Unless mitigating actions can be taken to address these issues, it is likely that the species will continue to decline.

6. Recommendation

TSSC recommends that the list referred to in section 178 of the EPBC Act be amended by including in the list in the vulnerable category:

Neophoca cinerea (Australian Sea-lion)

Publications used to assess the nomination

Department of the Environment & Heritage (2001). Neophoca cinerea Australian Sea-lion, in Species Profiles and Threats Database, Department of the Environment & Heritage, Canberra.

Evans, K. (2004). Concentrations of organochlorins in sperm whales (Physeter macrocephalus) from Southern Australian waters. Marine Pollution Bulletin 48, 486-503.

Evans, K. (2003). Pollution and marine mammals in the Southern Hemisphere: Potential or present threat? In: Marine Mammals: Fisheries, Tourism and Management Issues (eds. N. Gales, M. Hindell & R. Kirkwood), p 400-441. CSIRO Publishing, Collingwood, Victoria.

Goldsworthy, S.D., Bulman, C., He, X., Larcombe, J. & Littnan, C (2003). Trophic interactions between marine mammals and Australian fisheries: an ecosystem approach. In: Marine Mammals: Fisheries, Tourism and Management Issues (eds. N. Gales, M. Hindell & R. Kirkwood), p 62-69. CSIRO Publishing, Collingwood, Victoria.

Ling, J.K (1992). Neophoca cinerea. Mammalian Species number 392, The American Society of Mammalogists.

Page, B., McKenzie, J., McIntosh, R., Baylis, A., Morrissey, A., Calvert, N., Haase, T., Berris, M., Dowie, D., Shaughnessy, P.D. & Goldsworthy, S.D. (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 (in press).

Shaughnessy, P.D. (1999). The Action Plan for Australian Seals. Canberra, Environment Australia.

Shaughnessy, P.D., McIntosh, R., Goldsworthy, S.D., Dennis, T.E. & Berris, M. (in prep, currently undergoing peer review). Trends in abundance of Australian sea lions, Neophoca cinerea, at Seal Bay, Kangaroo Island, South Australia.

Shaughnessy, P.D., Dennis, T.E. & Seager, P.G. (in prep, submitted to Wildlife Research in July 2003). Status of Australian sea lions, Neophoca cinerea, and New Zealand fur seals, Arctocephalus forsteri, on Eyre Peninsula and the far west coast, South Australia.

Conservation Advice

The Australian Sea-lion (Neophoca cinerea) has a fragmented distribution along the coast and offshore islands of South Australia and southern Western Australia. The main threats to the Australian Sea-lion are mortality due to interactions with fisheries, aquaculture and entanglement with marine debris. An additional possible threat is competition for resources with the New Zealand Fur-seal.

The draft National Seal Strategy, currently under development, aims to address issues arising from interactions of pinnipeds with fisheries. The national Bycatch Action Plans, being produced by the Australian Fisheries Management Authority for eight of Australia's largest Commonwealth fisheries seeking to reduce pinniped interaction with fisheries. Finally, the ecological sustainability assessments of fisheries, undertaken by the Department of Environment and Heritage, also address this issue.

Priority recovery and threat abatement actions required for this species include:

  • Conduct further research and monitoring of the species to clarify the key threats;
  • Protect existing breeding habitats
  • Minimise the interactions between Australian Sea-lions and fishing operations (e.g. gill net, long line, drop line and lobster and cray pot fisheries)
  • Collect mandatory reporting data
  • Identify populations most affected
  • Utilise Seal Exclusion Devices (SEDs), or other modified gear to exclude Australian Sea-lions
  • Use plastic-free bait boxes
  • Minimise the interactions between Australian Sea-lions and aquaculture operations;
  • Establish reporting protocols for interaction between Australian Sea-lions and aquaculture in co-operation with states and industry
  • Identify populations most affected
  • Avoid Australian Sea-lion colonies when siting new operations
  • Use enclosures which cannot be breached by sea-lions or seals
  • Monitor recruitment, entanglement and mortality of the species to determine effectiveness of management policies.

This list does not encompass all actions that may be of benefit to this species, but highlights those that are considered to be of the highest priority at the time of listing.

Priority for the development of recovery plan: The development of a recovery plan is a high priority for this species, as the full range of threats to the Australian Sea-lion requires investigation. The greatest benefit to the Australian Sea-lion in the short term will be achieved through an expeditious reduction of mortality caused by fisheries interactions and entanglement with marine debris.