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Description |
Geographic Range [top]
Range Description: A. laevis (including the subspecies A. l. pooleorum) occurs throughout tropical northern Australia from Shark Bay, Western Australia to the southern Great Barrier Reef, east Australia (Cogger 2000). Its distribution extends east to the Coral Sea (Heatwole 1975) and Chesterfield Reefs (Minton and Dunson 1985) and New Caledonia (Ineich and Rasmussen 1997). It has also been reported from the southern New Guinea coastline (OShea 1996).
Countries occurrence:
Native:
Australia; Indonesia; New Caledonia; Papua New Guinea
FAO Marine Fishing Areas:
Native:
Indian Ocean – eastern; Pacific – western central
Additional data:
? Lower depth limit (metres): 70
Range Map: Click here to open the map viewer and explore range.
Population [top]
Population: This is the most commonly found sea snake species on coral reefs of Australia (Lukoschek et al. 2007a, Heatwole and Lukoschek 2008). Surveys of reefs in the southern Great Barrier Reef indicate that there have been some local population extinctions (at the level of individual reefs) over the last 30 years (Lukoschek et al. 2007a). There are also indications of larger-scale metapopulation dynamics for A. laevis in this region, thus it is unclear whether local extinctions indicate an overall decline in abundance or represent temporal fluctuations in the population (Lukoschek et al. 2007a). This species has also declined in abundance at Ashmore Reef in the Timor Sea, as have all other sea snake species at Ashmore Reef (Guinea 2006, 2007). Similarly, anecdotal information suggests that there has been a decline in abundance of sea snakes, including A. laevis, on some Coral Sea reefs over the past 20 years (H. Marsh pers. comm. 2009) however, dedicated surveys are needed to confirm this. The status of populations at other locations throughout this species’ range appears to be stable or is unknown.
Quantitative assessment of the impacts of trawling has shown that trawl mortality was not imposing a significant risk for this species at current levels of fishing effort in the Northern Prawn Fishery of Australia (Milton et al. 2008).
Current Population Trend: Decreasing
Additional data:
? Population severely fragmented: No
Habitat and Ecology [top]
Habitat and Ecology: This species occurs primarily around coral reefs where it is found in many habitat types including the reef crest, slope, edge, and over sandy bottoms adjacent to outer shallow and deeper reefs, as well as in lagoonal areas. It also occurs in inter-reefal habitats, but is much more common in close proximity to reefs. It has been recorded to depths of up to 68 m (M. Cappo pers. comm. 2009, T. Courtney pers. comm. 2009), although it more typically occurs at depths ranging from 10 to 40 m (V. Lukoschek pers. comm. 2009).
Individuals occupy linear home ranges along the vertical edges of coral reefs which overlap extensively with those of other individuals (Limpus 1975, Burns and Heatwole 1998). The snakes shelter in or under coral, sitting quietly and swaying in the current. They do not seem to return to the same shelter sites (Burns and Heatwole 1998). Mark recapture, sonic tracking and visual mapping studies of A. laevis from the Swain Reefs indicated that these snakes generally confine their movements to particular sections of reef (home ranges of about 0.18 ha for females and 0.15 ha for males) (Marsh et al. 1993).
This species feeds on crabs, prawns, fish eggs, and fish (Limpus 1975, Guinea 2007). It hunts in crevices at the junction of a coral or rock wall and in the sand substrate (Heatwole et al. 1978, Burns and Heatwole 1998).
Female Olive Sea Snakes are thought to reach sexual maturity at 4-5 years (Heatwole 1997) and may live to an estimated age of 15 years (Burns 1984). Larger older female sea snakes produce larger broods (Fry et al. 2001).
Systems: Marine
Congregatory: Congregatory (and dispersive)
Threats [top]
Major Threat(s): The main potential threats to A. laevis are loss and/or degradation of coral reef habitats and bycatch in trawling.
This species is strongly associated with coral reefs and the degradation of this habitat is likely to pose a threat to species persistence. Mass coral bleaching occurs in association with episodes of elevated sea surface temperature and results in significant losses of live coral (Hoegh-Guldberg 1999). This reduces habitat complexity, with a consequent decrease in prey abundance (Pratchett et al. 2008) and the loss of refuge sites. Climate change may thus threaten all sea snakes which are coral reef specialists (Francis 2006).
This species also is potentially at risk from their incidental capture in trawls in Australia. It is captured in trawl fisheries throughout its range (Courtney et al. 2010, Milton et al. 2008, Ward 2000) and has the lowest capacity to sustain fishing mortality of any sea snake species caught in Australian trawl fisheries (Milton 2001). It is has poor survival from trawling (~10% were landed dead and post-trawl deaths were ~20%) (Courtney et al. 2010). Many individuals are caught before they breed. This is partly due to the life history traits of A. laevis: which does not reach sexual maturity until age 4-5 years (Burns 1985). In addition, this species has low reproductive output (2-6 offspring every second year) (Burns 1985) and catch data suggests that a large proportion of the fished populations are incidentally captured (Milton 2001). Therefore, this species is unlikely to sustain additional mortality from incidental capture in trawls (Milton 2001).
Conservation Actions [top]
Conservation Actions: There are no species-specific conservation measures in place. No sea snake species is currently listed by CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora).
Sea snakes are protected in Australia since their addition to the ‘Listed Marine Species’ by the Department of Environment and Water Resources in 2000. They are protected in Australia under the Environment Protection Biodiversity and Conservation Act (EPCB) of 1999. This requires that all Australian industries interacting with protected species, directly or indirectly, demonstrate sustainability for the species impacted by their activities (Milton et al. 2008). The Australian Fisheries Management Act 1991 requires fishing efforts to avoid captures of threatened and protected species such as sea snakes.
The Northern Prawn Fishery (NPF) in Australia is having the largest impact on protected sea snake populations of any Commonwealth-managed fishery. The EPBC Act, and the NPF’s commitments under its Strategic assessment by the Department of the Environment and Water Resources, led to a three year study on developing and implementing a long-term bycatch monitoring program for Australia’s NPF (Milton et al. 2008).
Since 2003, Australias Commonwealth Scientific and Industrial Research Organization (CSIRO) and Australias Fisheries Management Authority (AFMA) have jointly run industry workshops to train crew member observers in the identification, photographing and recording of information on sea snakes caught in the NPF tiger and banana prawn seasons.
Commercial trials of different Bycatch Reduction Devices (BRDs) used in the Northern Prawn Fishery of Australia showed that two devices, Fisheye and Popeye Fishbox BRDs, can reduce sea snake catch by between 40 and 85% (without significant prawn loss) when set closer to the cod end than the maximum legally required distance, but <10% of fishers have responded to these findings by moving their BDRs closer to the codend (Milton et al. 2008).
Citation: Lukoschek, V., Courtney, T., Milton, D. & Guinea, M. 2010. Aipysurus laevis. The IUCN Red List of Threatened Species 2010: e.T176704A7286736. http://dx.doi.org/10.2305/IUCN.UK.2010-4.RLTS.T176704A7286736.en. Downloaded on 10 October 2018.
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