|Scientific Name:||Hydrophis elegans (Gray, 1842)|
Aturia elegans Gray, 1842
Leioselasma elegans (Gray, 1842)
|Taxonomic Notes:||This species has a highly variable colour pattern throughout its range and, as currently recognized, may comprise a complex of two or more species (Cogger 1975, A. Rasmussen pers. comm. 2009). Juveniles may represent major difficulties in identification. Is sometimes treated under the genus Leioselasma.|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Milton, D., Courtney, T., Guinea, M. & Lukoschek, V.|
|Reviewer(s):||Livingstone, S.R., Elfes, C.T., Polidoro, B.A. & Carpenter, K.E. (Global Marine Species Assessment Coordinating Team)|
H. elegans is endemic to Australasian waters. This species is abundant throughout its range. It lives in a range of marine habitats. Trawl bycatch data shows that it comprises a large component of the sea snake fauna in the Northern Trawl Fishery and a smaller component in the Queensland Trawl Fishery. The mortality rate in the Queensland Trawl Fishery was 12.4%. Although this species was found to have an elevated risk of over-fishing in the Queensland Trawl Fishery, there is no evidence to suggest that it is currently threatened. Quantitative assessment of the impacts of trawling has shown that trawl mortality has not caused significant declines that would reach the thresholds for a threatened category. Due to the wide distribution across most of northern Australia, the impact of bycatch is probably low. This species is listed as Least Concern.
|Range Description:||H. elegans is endemic to Australasian waters. Its distribution extends around northern Australia from New South Wales on the east coast of Australia (Cogger 1975, Limpus 1975) throughout the Great Barrier Reef, Gulf of Carpentaria and Arafura Sea to at least Broome on the west coast (Cogger 1975). It has also been recorded from around the coast of New Guinea (Cogger 1975, Heatwole 1999). This species' range extends further into Australia's temperate waters than the ranges of most other sea snake species.|
Native:Australia; Indonesia; Papua New Guinea
|FAO Marine Fishing Areas:|
Indian Ocean – eastern; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||This species is abundant throughout its range (Cogger 1975, Heatwole 1975, Limpus 1975, Rasmussen 2001), and trawl bycatch data suggest that it often comprises a large component of the sea snake fauna in soft sediment marine habitats throughout its range (Redfield et al. 1978; Ward 1996a,b, 2000; Wassenberg et al. 1994; Courtney et al. 2005, 2010; Milton et al. 2008). Trawl bycatch data also indicate that population abundances are spatially and temporally variable, as is the case with almost all Hydrophiine sea snake species.|
Trawl catch data of sea snakes were collated from research and commercial sampling from the Northern Prawn Fishery between 1976 and 2007 (Milton et al. 2008). The results showed that the abundances of most species, including H. elegans, and all sea snake species combined have been relatively stable over the last 30 years. There was a major reduction in the size of the fleet in 2007 and there are currently only 52 vessels operating, compared with 96 vessels in 2006. This change in the level of fishing effort will further reduce the impact of trawling on sea snakes and add confidence to the assessment that current trawl catches are not adversely impacting populations in northern Australia.
|Current Population Trend:||Stable|
|Habitat and Ecology:||H. elegans is a generalist species that occurs in a variety of soft sediment habitat types throughout its range, including sand, muddy sand, and mud. It sometimes ascends rivers (Heatwole 1975), thus it also occurs in freshwater habitats. Individuals occasionally also occur on coral reefs and sometimes rest in seagrass beds (M. Guinea, pers. comm. 2009). H. elegans is a generalist feeder and its diet includes squid and fish (Fry et al. 2001, Limpus 1975). It is commonly found at depths between 3.7-26 m (Redfield et al 1978), but may be found in water less than 2 m to about 80 m (Limpus 1975). There are records for depths of 110 m from the Queensland fishery (Courtney et al. 2010) and 90 m in Broome (A. Rasmussen pers. comm. 2009).|
H. elegans is by far the longest of all sea snake species. Reproductive output in the Great Barrier Reef (GBR) and the Northern Prawn Fishery (NPF) is approximately 12-13 offspring per clutch every 2-3 years (Fry et al. 2001, Ward 2001). The number of offspring per clutch is variable and increases with the length of the female, which can range from 110 to >200 cm (standard ventral length) at maturity (Fry et al. 2001).
|Generation Length (years):||7|
The preferred habitat of this species overlaps with trawl fisheries. As such, it is a significant component of trawler bycatch in northern and eastern Australia (Redfield et al. 1978; Ward 1996a,b, 2000; Wassenberg et al. 1994; Milton et al. 2008; Courtney et al. 2010) and is commonly caught in all trawl fisheries in depths of 100 m or greater (Courtney et al. 2010).
In the Queensland trawl fisheries, it has been caught from every sector of the fishery and makes up 5% of the incidental capture. Mortality rate was estimated at 12.4% (Courtney et al. 2010). The post-trawl mortality was low.
According to Courtney et al. (2010), the risk of overfishing of sea snakes in the Queensland trawl fisheries to the point of recruitment failure and population declines for appears low for all species. The risk of localized extinction on the east coast of Australia due to trawling also appears unlikely. However, an anti-conservative methodology was used to calculate the risk, and therefore should be considered preliminary and speculative assessments (Courtney et al. 2010). H. elegans was found to have the highest risk of over-fishing of all species (C/M=0.59). This is not thought to be due to the high proportion of its distribution that is trawled (29% was exposed to trawling), but rather that it had the lowest value of M (natural mortality). In general, species with low rates of M are more prone to overfishing than species with high rates (Milton et al. 2008). This low value of M is possibly attributed to the large size that H. elegans attains. Post-trawl mortality analysis indicated that larger snakes experience higher post-trawl mortality, and hence, may be more vulnerable. The higher risk figure for H. elegans indicates that the level of incidental fishing mortality is above that required for maximum sustainable yield, however Courtney et al. (2010) states that this does not imply a high or imminent risk of extinction from the Queensland east coast. In practice, H. elegans was found to have negligible (< 0.001) post-trawl mortality; but this was based on a sample of only eight individuals.
Quantitative assessment of the impacts of trawling on the populations of sea snakes in the Northern Prawn Fishery has shown that trawl mortality was below reference points and no species appears to be at risk at current levels of fishing effort (Milton et al. 2008). Due to the wide distribution across most of northern Australia, the impact of bycatch for this species is probably low (Milton et al. 2008).
No sea snake species is currently listed by CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora). In addition, there currently are no specific conservation or management plans for any sea snake species. Sea snakes are protected in Australia as "Listed Marine Species" under the Environment Protection Biodiversity and Conservation Act 1999 (EPBC Act). The provisions of the EPBC Act requires that all Australian industries interacting with protected species (including "Listed Marine Species", directly or indirectly demonstrate sustainability for the species impacted by their activities (Milton et al. 2008). In addition, the 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 has the largest impact on sea snake populations of any Commonwealth-managed fishery. The EPBC Act and the NPFs commitments under its Strategic Assessment by the Department of the Environment and Water Resources, led to the start of a three year study on developing and implementing a long-term bycatch monitoring program for Australias NPF. Since 2003, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Australian Fisheries Management Authority (AFMA) have jointly run industry workshops to train crew-member observers in the identification, photography 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 Australias trawl fisheries 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 minimum legally required distance, but <10% of fishers have responded to these findings by moving their Bycatch Reduction Devices closer to the cod end (Milton et al. 2008). Recommendation would be to reduce the number of individuals taken as bycatch in the prawn trawl fishery using appropriate exclusion devices and placement within nets (Courtney et al. 2009, Milton et al. 2008, E. Fletcher pers. comm. 2009).
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Courtney, A. J., Schemel, B.C., Wallace, R., Campbell, M.J., Mayer D.G. and Young, B. 2010. Reducing the impact of Queensland's trawl fisheries on protected sea snakes. Fisheries Research and Development Coorporation (FRDC) Project #2005/053 Final Report.
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Heatwole, H. 1999. Sea Snakes. Krieger Publishing Company, Malabar, Florida.
IUCN. 2010. IUCN Red List of Threatened Species (ver. 2010.4). Available at: http://www.iucnredlist.org. (Accessed: 27 October 2010).
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Milton, D., Zhou, S., Fry, G. and Dell, Q. 2008. Risk assessment and mitigation for sea snakes caught in the Northern Prawn Fishery. Final report. CSIRO, Cleveland, Queensland.
Rasmussen, A.R. 2001. Sea Snakes. The Living Marine Resources of the Western Central Pacific, Food and Agriculture Organization of the United Nations, Rome.
Redfield, J.A., Holmes, J.C. and Holmes, R.D. 1978. Sea snakes of the eastern Gulf of Carpentatria. Australian Journal of Marine and Freshwater Research 29(3): 325-334.
Ward, T.M. 1996. Sea snake bycatch of fish trawlers on the northern Australian continental shelf. Marine and Freshwater Research 47: 625-630.
Ward, T.M. 1996. Sea snake bycatch of prawn trawlers on the northern Australian continental shelf. Marine and Freshwater Research 47: 631-635.
Ward, T.M. 2000. Factors affecting the catch rates and relative abundance of sea snakes in the by-catch of trawlers targeting tiger and endeavour prawns on the northern Australian continental shelf. Marine and Freshwater Research 51: 155-164.
Ward, T.M. 2001. Age structures and reproductive patterns of two species of sea snake, Lapemis hardwikii Grey (1836) and Hydrophis elegans Grey (1842), incidentally captured by prawn trawlers in northern Australia. Marine and Freshwater Research 52: 193-203.
Wassenberg, T.J., Milton, D.A. and Burridge, C.Y. 2001. Survival rates of sea snakes caught by demersal trawlers in northern and eastern Australia. Biological Conservation 100: 271-280.
|Citation:||Milton, D., Courtney, T., Guinea, M. & Lukoschek, V. 2010. Hydrophis elegans. The IUCN Red List of Threatened Species 2010: e.T176734A7292879.Downloaded on 23 April 2018.|
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