Issues Paper for the Australian Sea Lion
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| Issues Paper for the
Australian Sea Lion (Neophoca cinerea) 2013
The recovery plan linked to this issues paper is obtainable from: www.environment.gov.au/coasts/species/seals/index.html © Commonwealth of Australia 2013 This work is copyright. You may download, display, print and reproduce this material in unaltered form only (retaining this notice) for your personal, non-commercial use or use within your organisation. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. Requests and enquiries concerning reproduction and rights should be addressed to Department of Sustainability, Environment, Water, Population and Communities, Public Affairs, GPO Box 787 Canberra ACT 2601 or email public.affairs@environment.gov.au. Disclaimer While reasonable efforts have been made to ensure that the contents of this publication are factually correct, the Commonwealth does not accept responsibility for the accuracy or completeness of the contents, and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of
Images credits Front cover left to right: entangled Australian sea lion, close up image of Australian sea lion, colony of Australian sea lions, Australian sea lion on the water’s surface – Derek Hamer, Australian sea lion underwater – David Muirhead Back cover left to right: Australian sea lion on a rocky shore, close up image of Australian sea lion, Australian sea lion on the water’s surface – Derek Hamer Contents
1 Summary 6 2 Introduction 8 2.1 Purpose 8 2.2 Objectives 8 2.3 Scope 8 2.4 Sources of information 8 2.5 Recovery planning process 9 3 Biology and ecology 10 3.1 Species description 10 3.2 Distribution, abundance and trends 10 3.3 Foraging ecology and diet 15 3.4 Life history, breeding strategies and population genetics 19 4 Conservation status 22 5 Immediate and known conservation threats 24 5.1 Primary threats 25 5.2 Secondary threats 33 6 Summary of issues 41 7 References 42 8 Appendices 54 Appendix 1: Known breeding sites for the Australian sea lion and range of pup counts 54 List of figures Figure 1: Breeding distribution of the Australian sea lion, indicating the location and approximate pup number range of the 76 sites where Australian sea lion pups have been recorded. The number of sites with each pup number range is given in parentheses. Depth contours of 200, 500, 1000 and 2000m (light to dark blue) are indicated (updated from DEWHA, 2010). 11 Figure 2: Trends in Australian sea lion pup abundance at Seal Bay (Kangaroo Island, South Australia), for 18 consecutive breeding seasons between 1985 and 2010 13 Figure 3: Trends in Australian sea lion pup abundance at Dangerous Reef (Spencer Gulf, South Australia), for 12 of 22 breeding seasons between 1975 and 2007. 14 Figure 4: Geographic distribution of foraging (at-sea) effort of 115 tracked lactating female Australian sea lions across South Australian shelf waters (high: red, medium: orange, low: blue) 16 Figure 5: Predicted timing of breeding for the Australian sea lion, depicting the seasonal drift in the peak of breeding across the entire year at Seal Bay between 2001 and 2020. 20 Figure 6: Geographic representation of genetic differentiation among Australian sea lions 21 Figure 7: Australian sea lions observed entangled at breeding colonies. 32 List of tables Table 1: Prey species identified in the diet of Australian sea lions, derived from feeding trials of captive animals and from stomach analysis of opportunistically collected carcasses. 18 Table 2: Current conservation listings for the Australian sea lion in Australia 23 Table 3: The location of known breeding sites for the Australian sea lion and range of pup counts over the 23 years from 1985. 54 Abbreviations AFMA Australian Fisheries Management Authority, Commonwealth DSEWPaC The Department of Sustainability, Environment, Water, Population and Communities, Commonwealth EPBC Act Environment Protection and Biodiversity Conservation Act 1999 IUCN International Union for Conservation of Nature MARPOL International Convention for the Prevention of Pollution from Ships SESSF Southern and Eastern Scalefish and Shark Fishery SLED Sea Lion Exclusion Devices WTO Wildlife Trade Operation 1 Summary The Australian sea lion (Neophoca cinerea) was listed as vulnerable under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act 1999) in 2005 and as endangered on the International Union for Conservation of Nature (IUCN) Redlist in 2008. The Department of Sustainability, Environment, Water, Population and Communities (DSEWPaC), with the assistance of key stakeholders, has drafted a recovery plan for
The Australian sea lion was hunted commercially during the 1700s and 1800s and has not recovered to occupy its former range since that time. It is expected that the lack of recovery of the species is a result of life history characteristics coupled with contemporary threats. The Australian sea lion exhibits low fecundity compared with other pinnipeds, due to a prolonged 17–18 month breeding cycle. Breeding populations are typically small and breeding colonies are unlikely to receive female immigrants due to breeding site fidelity (i.e. philopatry), suggesting that recolonisation of extinct breeding colonies is unlikely, and many breeding colonies (or clusters of colonies) have become genetically distinct as a result. This issues paper has been developed to support the Recovery Plan for the Australian Sea Lion and is a summary of a more detailed Australian Sea Lion Technical Issues Paper, developed in 2010 (DEWHA, 2010). This issues paper summarises the biology and ecology of the Australian sea lion and details the immediate and identifiable threats to the species, and recommendations for future research. A range of anthropogenic factors have been identified which may be impacting on the recovery of the Australian sea lion. The cumulative impact of many of these threats varies across the range of the species, with some threats having more prominence in certain areas. Fisheries bycatch and entanglement in marine debris appear to pose the greatest threat to the Australian sea lion at present. Secondary threats include habitat degradation and interactions with aquaculture operations; human disturbance to colonies; deliberate killings; disease; pollution and oil spills; noise pollution; prey depletion and climate change. Considerable research and actions undertaken in recent times provide a clear step forward in our knowledge of the biology and ecology and in the conservation management of the Australian sea lion. Continuation of research into the ecology and biology, as well as into causes of anthropogenic mortality, will assist in developing programs to aid the long term recovery of this species. This issues paper should be read in conjunction with the accompanying 2013
2 Introduction 2.1 Purpose The purpose of this paper is to provide a summary of the biology, population ecology and current threats to the Australian sea lion in Australian waters and to make recommendations on the future research necessary to protect this species. This paper is an updated summary of a more detailed Australian Sea Lion Technical Issues Paper produced in 2010 (DEWHA, 2010). It has been written to inform the development of the Recovery Plan for the Australian Sea Lion and is designed to be read in conjunction with the Plan. 2.2 Objectives The objectives of this paper are to: collate information on the distribution, abundance and trends of Australian sea lion populations and on the various natural and anthropogenic factors that impact on them identify gaps in the available information identify areas of further research to address the identified information gaps. 2.3 Scope This document provides a contemporary picture of the biology and ecology of the Australian sea lion and identifies threats to its long-term persistence in the wild. This document is not a recovery plan and does not prescribe management actions necessary to address population declines. 2.4 Sources of information This document summarises, synthesises and updates information included in a more
2.5.1 Purpose of recovery plans The Australian Government minister responsible for the environment may make or adopt recovery plans for threatened fauna, threatened flora (other than conservation dependent species) and threatened ecological communities listed under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). Recovery plans set out the research and management actions necessary to stop the decline of, and support the recovery of, listed threatened species or threatened ecological communities. The aim of a recovery plan is to maximise the long term survival in the wild of a threatened species or ecological community. 2.5.2 Objectives of the Recovery Plan for the Australian Sea Lion The overarching objective of the 2012 Recovery Plan for the Australian Sea Lion is to halt the decline and assist the recovery of the Australian sea lion throughout its range in Australian waters by increasing the total population size, while maintaining the number and distribution of breeding colonies with a view to: improving the population status, leading to future removal of the Australian sea lion from the threatened species list of the EPBC Act ensuring that anthropogenic activities do not hinder recovery in the near future or impact on the conservation status of the species in the future. 3 Biology and Ecology The Australian sea lion is one of seven extant sea lion species worldwide (Boness, 2009) and is Australia’s only endemic pinniped species and one of the rarest otariids (Ling, 2002). The Australian sea lion shares Australia’s southern coastline with the Australian fur seal (Arctocephalus pusillus doriferus), which is a subspecies with the South African or cape fur seal (Arctocephalus pusillus pusillus) and the New Zealand fur seal (Arctocephalus forsteri). At birth, the pelage of pups is dark chocolate brown to charcoal grey in colour for the first five months, before changing to a grey-brown colour on the dorsal and lateral surfaces and cream on the chest and cheeks (Shaughnessy, et al., 2005). The females retain this colouration for life, although subadult males gradually develop a darker chest with evident scars from sparring with other subadult males and a darker face. The pelage colour of fully grown bulls becomes much darker brown, with the dorsal surface of the neck region (i.e. the mane) being light brown to cream. Pups are 62–68 cm long and weigh 6.4–7.9 kg at birth, while a pregnant female may be 132–181 cm long and weigh 61–105 kg, depending on the location (Ling, 2002; Hamer, et al., 2007). Bulls may attain lengths of 200 cm and weigh in excess of 200 kg (Ling, 2002). 3.2 Distribution, abundance and trends The current distribution of Australian sea lion breeding colonies extends along approximately 3500 kilometres of Australia’s southwest coastline, from the Houtman Abrolhos Islands on the west coast of Western Australia to The Pages Islands to the east of Kangaroo Island in South Australia (Figure 1; Appendix 1). The full historical extent of the Australian sea lions’ geographic range is unclear, although seal harvesting activities may have caused the extirpation of several breeding colonies within the current range, plus range retraction from the Bass Strait islands some 650–1000 kilometres southeast of The Pages Islands (Gales, et al., 1994; Ling, 1999; Shaughnessy, et al., 2005).
There are 76 known breeding sites for the Australia sea lion, with 28 in Western Australia and 48 in South Australia, of which 58 are known as regular breeding colonies (i.e. sites at which five or more pups per breeding cycle have been recorded; Shaughnessy, et al., 2011; Appendix 1) and 18 are sites where the presence of pups has been occasionally recorded (i.e. have fewer than five pups per breeding cycle; Shaughnessy, et al., 2011; Appendix 1). The 58 breeding colonies are considered as habitat critical to the survival of the species because they are used to meet essential life cycle requirements (i.e. breeding). The most recent pup abundance surveys indicate that an estimated 3622 pups are born per breeding cycle across the species range (Shaughnessy, et al., 2011). Pup numbers are used as the most reliable basis for determining population size. They are the age group most likely to be on shore because they have not developed at-sea foraging skills and are confined to breeding sites for at least the first five weeks of their life (McIntosh, et al., 2011; Shaughnessy, et al., 2011). The latest figure exceeds previous estimates of 2495 pups per breeding cycle during the early 2000s (McKenzie, et al., 2005) and 2432 pups per breeding cycle during the early
Population estimates have been calculated using a ‘pup multiplier’ of 4.08, which allows the recorded number of pups in a pinniped population to infer overall population size, based on population demographic data (Berkson & DeMaster, 1985). However, limited population demographic data is available for the Australian sea lion, originating from only one breeding site at Seal Bay (Kangaroo Island, South Australia), which may not be representative of the situation at other colonies (McIntosh, 2007; McIntosh, et al., 2011). Nonetheless, these currently available parameters suggest there are approximately 14 780 Australian sea lions across the species’ entire geographic range (Shaughnessy, et al., 2011). Long-term population monitoring through which trends can be determined has only occurred at a few breeding sites, although population monitoring at other sites has also been described in the 2010 Australian Sea Lion Technical Issues Paper (DEWHA, 2010). Seal Bay provides the most comprehensive account, with reliable estimates of pup abundance available since the mid-1980s (Shaughnessy, et al., 2006). Subsequent pup counts have indicated a general decline of 0.54–0.67 per cent per year between 1985 and 2010 (Shaughnessy, et al., 2006; Goldsworthy, et al., 2008a; Goldsworthy, et al., 2010; Goldsworthy, et al., 2011; Figure 2). Oscillations between years are attributable to the extended 17.6 month breeding cycle for this species (further explained in Section 3.4 of this document), with higher levels of pup mortality occurring when breeding occurs over winter months (McIntosh, 2007; Goldsworthy, et al., 2008a). Explanations for the long-term trend have focused on bycatch and entanglement of individuals in fishing gear (Page, et al., 2004). Figure 2: Trends in Australian sea lion pup abundance at Seal Bay (Kangaroo Island, South Australia), for 18 consecutive breeding seasons between 1985 and 2010 
(Source: Goldsworthy, et al., 2011, updated from Shaughnessy, et al., 2006). Regular population monitoring has also occurred at Dangerous Reef (Spencer Gulf, South Australia), with pup abundance estimates available for 12 of the 22 breeding cycles between 1975 and 2007 (Goldsworthy, et al., 2007a). The population there showed a moderate increase of 1.8 per cent per year until 1999, whereupon the rate of population growth increased to
in pup abundance due to increased pup mortality during winter breeding seasons was evident. The increase in the population growth rate is thought to be attributable to a ban on shark gillnetting in Spencer Gulf in 2001. The associated theory is that the impediment to growth was removed, with fewer or no lactating Australian sea lion females with dependent pups becoming bycaught and drowning in demersal shark gillnets after that time (Goldsworthy, et al., 2007a). Figure 3: Trends in Australian sea lion pup abundance at Dangerous Reef (Spencer Gulf, South Australia), for 12 of 22 breeding seasons between 1975 and 2007. 
(Note the marked increase in pup numbers after about 2000, around the time that demersal gillnetting for sharks was banned in Spencer Gulf (Source: Goldsworthy, et al., 2007a)). 3.3 Foraging ecology and diet It is difficult to identify the attributes of critical marine habitat for the Australian sea lion. Nonetheless, determination of geographic distribution of foraging effort and of vertical dive profiles provides some clues as to where individuals focus their time when at sea and when foraging. About 180 satellite transmitters have been deployed on individual Australian sea lions across their range, many being lactating females with dependent pups ashore, mostly across South Australian waters (Hamer, et al., 2007; Goldsworthy, et al., 2009b; Campbell, 2011). These studies identified marked individuality in foraging effort within and between the breeding sites from which the animals were tracked, with a variety of coastal and offshore habitats being utilised. The mean maximum foraging distances achieved from each colony ranged from 28 ± 18 km at Dangerous Reef in Spencer Gulf to 189 ± 25 km at Bunda Cliffs in exposed waters near the Western Australian border (Fowler, et al., 2007; Hamer, et al., 2013). For 115 lactating females tracked in South Australian waters, at-sea foraging effort covered 27.9 per cent of the approximately 178 000 km2 area of South Australian shelf waters, from coastal areas out to the shelf break (Hamer, et al., 2013; Figure 4). These results suggest the utilisation of shelf waters in South Australia — and across the entire range of the species generally — is likely to be extensive, although variable depending on the environmental conditions in the local marine environment. Foraging capacity of the Australian sea lion develops with age, with 15 month old pups foraging nearer their natal colony (mean distance 20.8 ± 4 km) when compared with adults (67.9 ± 3.5 km; Fowler, et al., 2007). However, several marked pups have been shown to move from Dangerous Reef to English Island, some 20 km to the north, at approximately three months of age (Goldsworthy, et al., 2009b). This suggests that the development of at-sea foraging behaviours may vary between breeding colonies and may also depend on localised environmental conditions. Figure 4: Geographic distribution of foraging (at-sea) effort of 115 tracked lactating female Australian sea lions across South Australian shelf waters (high: red, medium: orange, low: blue) In (a) the Great Australian Bight, (b) Nuyts Archipelago, (c) southern Eyre and (d) Kangaroo Island regions (Source: Hamer, et al., 2013).  
a b  
c d Unlike the sympatric New Zealand fur seal that will forage predominantly in the pelagic zone (Harcourt, et al., 2002), the Australian sea lion spends around 35 per cent of its time at or close to the sea floor (Costa & Gales, 2003). Adults tend to travel at the surface for a short distance, then commence repeated dives to the benthos (Goldsworthy, et al., 2009b). The descent and ascent appear to be rapid, presumably to maximise the time spent on the sea floor. Diving capacity also develops with age, with the mean depth and duration of dives continuing to increase from six months of age (7 ± 1 m and 0.4 ± 0.2 min) to adulthood (71 ± 4 m and
The diet of the Australian sea lion comprises mostly benthic species. Unlike fur seals, from which hard part remains in scats such as fish otoliths and squid beaks can be used to determine dietary composition, Australian sea lion scats seldom contain identifiable prey remains. However, feeding trials of captive animals and stomach analysis of opportunistically collected deceased animals have facilitated the identification of many benthic and bentho-pelagic prey (Walker & Ling, 1981; Gales, et al., 1992; Ling, 1992; McIntosh, et al., 2006; Table 1). More recent studies of stomach remains confirmed octopus and giant cuttlefish as the most numerically abundant prey items at Seal Bay, although diet at other sites may differ (McIntosh, et al., 2006). Fatty acid and DNA analyses have confirmed the presence of the prey groups outlined in Table 1 at a molecular level, using milk and scat samples. Fatty acid analysis has also suggested that inshore foragers had fish and shark-dominated diets, while offshore foragers had fish-dominated diets (Peters, et al., 2007; Baylis, et al., 2009). The seagrass meadows in South Australia are some of the largest in the world (Shepherd & Robertson, 1989) and are likely to offer an important habitat to many of these prey species. Given that the Australian sea lion spends a considerable amount of time foraging in them, the loss of seagrass beds due to climate change may have negative ramifications for the Australian sea lion (Goldsworthy, et al., 2009b; Lowther, et al., 2011; refer: section 5.2.10). Table 1: Prey species identified in the diet of Australian sea lions, derived from feeding trials of captive animals and from stomach analysis of opportunistically collected carcasses. The most numerically abundant prey (*) are marked.
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