Aipysurus fuscus 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Reptilia Squamata Elapidae

Scientific Name: Aipysurus fuscus (Tschudi, 1837)
Common Name(s):
English Dusky Sea Snake, Timor Reef Snake
French Aipywure Brun
Stephanohydra fusca Tschudi, 1837

Assessment Information [top]

Red List Category & Criteria: Endangered A2ac; B2ab(iii,v) ver 3.1
Year Published: 2010
Date Assessed: 2009-02-15
Assessor(s): Lukoschek, V., Guinea, M., & Rasmussen, A.
Reviewer(s): Livingstone, S.R., Elfes, C.T., Polidoro, B.A. & Carpenter, K.E. (Global Marine Species Assessment Coordinating Team)
A. fuscus  has only been reliably reported from four or five reefs in the Timor Sea, and given its shallow depth range,  has an area of occupancy estimated to be less than 500 km². This species was the second most common sea snake recorded at Ashmore Reefs in 1998, when catch rate of snakes per hour were 14 snakes per hour. In 2002, less than 29 individuals were found and catch rates drastically decreased to one snake per hour in 2005. No individuals were recorded from any reef in 2007. Although more survey work is needed, this species has recently undergone a large population decline of at least probably 70% in the past 15 years (three generation lengths) since 1998. Threats are largely unknown, however, declines are possibly due to habitat degradation from coral bleaching and decline of ecosystem health. This species is listed as Endangered.

Geographic Range [top]

Range Description:A. fuscus is an endemic species with small geographic range. It is found on Ashmore, Cartier,  Hibernia, Scott and Seringapatam Reefs in the Timor Sea between northwestern Australia and Timor (Heatwole 1999, Cogger 2000). Given its shallow depth range, it has an area of occupancy estimated to be less than 500 km².

The type specimen was collected from Sulawesi (Tschudi 1837). However, this collection location is questionable. There are no subsequent records of this species from Sulawesi or any other locations apart from Australian reefs in the Timor Sea. There is also no direct evidence that the type specimen is conspecific with A. fuscus on the Australian reefs (Cogger 1975). The location of the type specimen is, therefore, not being taken into account for this assessment (V. Lukoschek and A. Rasmussen pers. comms. 2009).

Countries occurrence:
Australia; Timor-Leste
FAO Marine Fishing Areas:
Indian Ocean – eastern; Pacific – western central
Additional data:
Estimated area of occupancy (AOO) - km2:500
Number of Locations:5
Lower depth limit (metres):12
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:A. fuscus occurs as no more than five subpopulations – Ashmore, Hibernia, Cartier, Scott and Serangipatan Reefs. Current population sizes are unknown. It is likely that there is very little movement between these subpopulations. Genetic studies of a far more widely distributed congener and sister species, Aipysurus laevis, indicates restricted gene flow between Ashmore, Hibernia and Cartier Reefs (Lukoschek et al. 2007b, 2008). A. laevis occurs in a much wider range of habitat types (including deeper water) than A. fuscus, thus it is likely that dispersal is more restricted for A. fuscus than for A. laevis.

Since 1998, records of sea snakes from Ashmore Reef, Australia have shown rapid decline (Francis 2006).  A. fuscus comprised between 3-22 % of the population at Ashmore Reef in 1994 (Guinea and Whiting 2005). In 2002, 29 individuals of this species were recorded in over three weeks of intensive surveying at Ashmore Reef and three individuals were recorded on Scott Reef in one day (V. Lukoschek pers. comm. 2009). In 1972 it comprised 10% of records of sea snakes at Ashmore Reef and 13% of sea snakes recorded from Scott Reef (Minton and Heatwole 1975). It comprised ~ 20% of a sample of sea snakes collected from Ashmore Reef in the 1920s (Smith 1926).

Sighting rates of this species at Ashmore Reef have been variable over the years, however, there seems to have been an overall decline in sightings since 1998. Standardized sighting rates at the inner mooring at Ashmore Reef are as follows: 1994 - one individual per hour; 1996 - three per hour; 1998 - 14 per hour; 2000- 10 per hour; 2003 - seven per hour; 2004 - one per hour; 2005 - no individuals of this species seen at the inner mooring (Francis 2006; Guinea 2006, 2007).

In 2002, only 29 individuals were recorded over three weeks on Ashmore Reef and three were recorded on Scott Reef in one day (V. Lukoschek pers. comm. 2009). This species was the second most common sea snake recorded at Ashmore Reefs in 1998 (Guinea and Whiting 2005). Catch rate of snakes per hour decreased from 14 snakes per hour in 1998 to one snake per hour in 2005. A. fuscus was still recorded in low numbers at other survey sites on Ashmore Reef and at Hibernia Reef in 2005 (Guinea 2006). It was not recorded from any reef in 2007 (Guinea 2007). As such, there are no estimates of its current population size, however, there appears to have been a decline of at least 70% since 1998. The reasons for the local extinctions of these populations are unknown. A possible threat could be unusually high water temperatures leading to severe coral bleaching and coral reef habitat degradation throughout the area (Francis 2006).The declines in abundance of this species on the Timor Sea reefs coincide with overall declines in all sea snakes species on these reefs (Francis 2006; Guinea 2006, 2007).
Current Population Trend:Decreasing
Additional data:
Population severely fragmented:Yes

Habitat and Ecology [top]

Habitat and Ecology:A. fuscus occurs in a range of reef habitats and primarily in shallow waters, although it is found in water depths up to 25 or 30 m (Minton and Heatwole 1975). It feeds mostly on small reef fishes from the families Labridae (wrasses), and Gobidae (gobies) as well as eels and fish eggs (Voris 1972, McCosker 1975, Rasmussen 2001).

Maximum size is typically 78 cm (Smith 1926, Francis 2006), though a specimen of 89 cm TL (A. Rasmussen pers. comm. 2009) and 96 cm SVL have been recorded (M. Guinea pers. comm. 2009).  Based on similar species, this species has a generation length of approximately five years, based on a longevity of approximately 10 years, and age of first maturity of 3-4 years.
Generation Length (years):5

Threats [top]

Major Threat(s): There are no specific, clearly identified or quantified past, current or future threats to A. fuscus or any other reef-associated sea snake species, and it is unclear why populations at Ashmore, Hibernia and Cartier Reefs have declined. A. fuscus is not targeted by fisheries; there is no evidence that it is being illegally harvested; and is it not subject to incidental bycatch (some sea snake species are routinely captured as by-catch in trawls, but this is not the case for strongly reef-associated species such as A. fuscus; Lukoschek et al. 2007a).

Nonetheless, something is clearly impacting this species and it is most likely that current and future threats relate to degradation or modification of shallow-water coral reef habitats from bleaching events due to increased sea surface temperatures. However, compared to other areas, the Ashmore Reef was not badly affected by the 1998 bleaching event (V. Lukoschek pers. comm. 2009), although it suffered severe bleaching in 2003 (Kaspartov et al. 2006). Thus, climate change may be a threat to some sea snake species (Francis 2006). In addition, increased water temperatures on the reef flat may exceed the upper lethal limit for A. fuscus, which has been reported to be 36°C for the sea snake Pelamis platurus (Graham et al. 1971).

Habitat degradation and modification may also result in possible reduction in prey species abundances (i.e. small coral reef fishes).

Conservation Actions [top]

Conservation Actions: No sea snake species is currently listed by CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora) and there are no specific conservation or management plans for any sea snake species in Australia.

Ashmore Reef has been a nature reserve since 1983 and has had various levels of monitoring against illegal fishing since that time.  Management plans that focused on protection of marine life did not come into effect until 1990 (Australian National Parks and Wildlife Service 1989), with a second management plan coming into effect in 2002 (Commonwealth of Australia 2002), and since 1998 protection has actively been enforced. However, these management plans have not specifically addressed threat abatement or recovery of any sea snake species. Nonetheless, these management plans are designed to protect marine biodiversity and habitat quality; however, there are no data to indicate how, or to what extent, these measures are providing threat abatement to A. fuscus.

Citation: Lukoschek, V., Guinea, M., & Rasmussen, A. 2010. Aipysurus fuscus. The IUCN Red List of Threatened Species 2010: e.T176763A7299535. . Downloaded on 23 May 2018.
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