In addition, proponents and land managers should refer to the Recovery Plan (where available) or the Conservation Advice (where available) for recovery, mitigation and conservation information.
|EPBC Act Listing Status||Listed marine|
|Adopted/Made Recovery Plans|
|Policy Statements and Guidelines||
Marine bioregional plan for the North-west Marine Region (Department of Sustainability, Environment, Water, Population and Communities (DSEWPaC), 2012y) [Admin Guideline].
Federal Register of
Declaration under section 248 of the Environment Protection and Biodiversity Conservation Act 1999 - List of Marine Species (Commonwealth of Australia, 2000c) [Legislative Instrument].
|Scientific name||Ephalophis greyi |
This is an indicative distribution map of the present distribution of the species based on best available knowledge. See map caveat for more information.
The current conservation status of the North-western Mangrove Seasnake, Ephalophis greyi, under Australian Government legislation, is as follows:
National: Listed as a marine species under the Environment Protection and Biodiversity Conservation Act 1999.
Scientific name: Ephalophis greyi
Common name: North-western Mangrove Seasnake
The North-western Mangrove Seasnake belongs to a monotypic genus. A monotypic genus is a taxonomic group containing only one biological type; the Ephalophis genus therefore contains one species.
The North-western Mangrove Seasnake is slender and grows to around 50 cm (Cogger 2000). Its upper (dorsal) surface is cream or pale olive-brown with about 2540 dark grey dorsal blotches which fuse to form an irregular and interrupted zigzag stripe along the vertebral line. Each band is broader than the paler interspaces. The head scales are large and regular and similar to that of a terrestrial elapid snake (Ehmann 1992b). The body scales are smooth and imbricate (overlapping) in the anterior and lateral regions, but develop blunt keels in the dorsal and posterior regions. They form 1921 rows at the mid-body. Ventral scales are 3.54 times as broad as neighbouring body scales and number 159171. The anal scale is divided. The subcaudal scales (near the tail) are single and number between 2733 (Cogger 2000).
In 2000, the North-western Mangrove Seasnake was only known from the north-western coast of Western Australia (Cogger 2000).
The species inhabits the intertidal zone of tidal creeks and flats of relatively compact mud or sandy mud with crab and mud skipper holes (Cogger 2000; Ehmann 1992b).
Sea snakes are air breathing reptiles and must come to the surface to breathe, however they can spend from 30 minutes to two hours diving between breaths. They have one elongate cylindrical lung that extends for almost the entire length of their body which is very efficient for gas exchange. They also carry out cutaneous respiration whereby oxygen diffuses from sea water across the snake's skin into the blood. The waste product, carbon dioxide, is then diffused out of the snake's body, via the skin (Heatwole 1999).
Sea snakes have nostril valves that prevent air entering the lung while underwater. Nostril valves open inwards and are held shut from behind by erectile tissue engorged with blood (Heatwole 1999).
Sea snakes are able to avoid excess salt accumulation from sea water using a salt excreting gland, known as the posterior sublingual gland, which sits under the tongue. Sea snakes shed their skin every two to six weeks, which is more frequently than land snakes and more often than needed for growth alone. The process involves rubbing the lips against coral or other hard substrate to loosen the skin. The snake's skin is then anchored to the substrate as it crawls forward, leaving the skin turned inside out behind it. Skin shedding allows sea snakes to rid themselves of fouling marine organisms such as algae, barnacles and bryozoans (Heatwole 1999).
The North-western Mangrove Seasnake, like most sea snakes, is viviparous, that is giving birth to live young (Cogger 2000). Male sea snakes have two penises called hemipenes, and each is an autonomous independently functioning penis, though only one is used during mating. Mating takes place for long periods and sea snakes must surface for air during that time. The female controls her breathing and, as she swims to the surface, the male is pulled along via the hemipenis. Males are unable to disengage until mating is finished (Cogger 2000; Heatwole 1999).
There is no information available on the clutch size or seasonality of reproduction for the North-western Mangrove Seasnake.
North-western Mangrove Seasnakes are known to feed on small fish, especially gobies. This species drifts with the rising tide and forages in crab holes for gobies as the holes are flooded (Ehmann 1992b).
Sea snakes that inhabit coral reefs and lagoons can be surveyed by travelling slowly (at about four knots) along transects in a small boat and visually identifying snakes observed within 3 m of the path of the boat. Species can be distinguished by this method if the water is up to 3 m deep. At low tide, surveys can be done on foot, for example by searching the reef flat along transects that are 1000 m long and 20 m wide (Guinea & Whiting 2005).
For close up identification, sea snakes that are swimming on the surface of the water can be captured using a dip net employed from a small boat (Limpus 1975). Snakes that are underwater and either active or resting can also be hand-netted by an individual snorkelling or scuba diving, using a cylindrical net 300 mm in diameter and 1700 mm long, with 10 mm mesh. With the aid of protective gloves the snake is gently grasped through the mesh at the base of the net, drawing the snake in until the top of the net can be twisted shut (Guinea & Whiting 2005; Guinea in press). Alternatively, snakes that are resting can be captured by grasping them behind the head and by the mid-body simultaneously. Pillstrom tongs and gloves can be used, although mechanical restraint may injure the snake and increase its aggressiveness (Heatwole 1975).
Little is known of the North-western Mangrove Seasnake and its possible threats (Cogger 2000).
Prawn trawling has been identified as a major threat to sea snakes due to: their life history (low fecundity and longevity); and demographic factors whereby much of the species' distribution coincides with those areas and depths where prawn trawling occurs (Marsh et al. 1993; Milton et al. 2009). Sea snakes are caught in the bycatch of trawls, and it is estimated that approximately 50% of individuals caught in trawls die by drowning or being crushed by the weight of the catch (Milton et al. 2009; Wassenberg et al. 2001). While sea snakes can naturally remain submerged for up to two hours, the conditions within the net will affect the sea snakes (Wassenberg et al. 2001). These conditions include the physical weight of the catch, the composition of the catch (including poisonous, spiny or abrasive animals) and the interaction of the catch with the seafloor. Survival has been found to depend on a few factors including when the sea snake enters the net (early or late in the tow), the duration of the trawl, the weight of the catch, how the sea snake is treated on the deck and the sea snake's morphology (Wassenberg et al. 2001).
Bycatch Reduction Overview
In the early 2000s, the mandatory use of Turtle Excluder Devices (TEDs) was introduced to all Australian trawl fisheries to reduce turtle bycatch. In addition, the Bycatch Reduction Devices (BRDs) were introduced to most Australian prawn trawl fisheries to reduce the bycatch of non-targeted species including sea snakes. BRDs are escape grids or openings designed to enable non-target marine animals to swim out of the net, while TEDs are hard grids placed in trawl nets to exclude turtles and other large animals. An illustration of these devices can be found here: TED/BRD. Both TEDs and BRDs assist in the conservation of sea snakes by: reducing the number of fish caught which decreases the weight of the catch, thus, reducing the physical damage to sea snakes caught in the nets; and, enabling sea snakes caught to escape (Wassenberg et al. 2001). As a result of the mandatory introduction of these devices, Australia’s state and commonwealth prawn trawl fisheries must now have both a TED and a second BRD installed in every trawl net (Courtney et al. 2010).
A range of studies have been conducted to evaluate the effectiveness of BRDs, as well as TEDs and BRDs used simultaneously, on sea snakes. For example, Wassenberg et al. (2001) suggested that the mortality rates should decline with the introduction of BRDs due to the reduced weight of the bycatch in nets as well as increased escapement by snakes. Brewer et al. (2006) concluded that the simultaneous use of TEDs and BRDs used by fishers in the Northern Prawn Fishery (NPF) had little effect (i.e. 5%) on excluding snakes from trawl nets. However, they found that the performance of BRDs alone could be improved if placed closer to the codend (the trailing end of the net where fish are finally caught). More recently, through improvement in design, the Fisheye BRD was similarly identified as capable of reducing sea snake bycatch and its effectiveness dependant on distance from the codend (Courtney et al. 2010). Testing of the Yarrow Fisheye BRD (Heales et al. 2008) and the Popeye Fishbox BRD (Raudzens 2007) in the NPF demonstrated their high potential for reducing sea snake catch rates with no adverse reduction in targeted prawn catch rates.
Prawn Trawling Crew Member Programs
Prawn trawling has been found to have a negative impact on protected sea snake populations (Milton et al. 2008). In 2003, a Crew Member Observer (CMO) program was established in the Northern Prawn Fishery (NPF). The program aimed to collect data on bycatch such as composition, catch rates and distribution during both NPF tiger and banana prawn fishing seasons. The initiative required the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and Australian Fisheries Management Authority (AFMA) to jointly run annual industry workshops to train the crew in the identification, photographing and recording of sea snakes from bycatch. During the 2003–2005 seasons, 21 crew member observers on 17 vessels collected data from 7602 prawn trawls. The observers recorded 4131 sea snakes from 12 species, with over half being photographed for identification and length estimation (Milton et al. 2008).
This CMO program has been used in conjunction with logbooks, requested industry collections, scientific observers and fishery-independent surveys for long term bycatch monitoring solutions, and reflects the NPF's commitment to the sustainability of all species impacted by its fishing activities (Milton et al. 2008).
Another research project (which ran between July 2005 and October 2007), established the Crew Member Program (CMP) to provide detailed information on the catch composition and catch rates of sea snake species and estimates of the within-trawl mortality rate of snakes in the Queensland otter and beam trawl fishery (Courtney et al. 2010). Sixty-seven crews collected data from all of the major east coast trawl fishing sectors. Additional data were obtained from research charters, research surveys and the fishery observer program. Detailed information was collected from a total of 8289 trawls that reported catching 3910 sea snakes. The study found that the highest catch of sea snakes was in redspot king prawn fishery due to an overlap with sea snake habitat.
Current Bycatch Reduction Methods and Effectiveness
Results from the CMP indicate that sea snake bycatch in the Queensland trawl fishery can be significantly reduced by using properly designed and installed BRDs, with no significant reduction in targeted prawn catch rates. Of the BRDs tested (the standard codend with no BRD, Fisheye BRD, square mesh codend BRD and square mesh panel BRD), the CMP found that the Fisheye BRD was the most effective device at excluding snakes i.e. 63% reduction compared to the standard net, with no significant effect on the catch rate of marketable (≥ 20 mm carapace length) prawns. The Fisheye BRD was also the most effective device for excluding bycatch of non-targeted species with a 33% reduction in bycatch rate compared to the standard net (Courtney et al. 2010). Furthermore, the square mesh codend was found to also be highly effective at excluding both sea snakes and other bycatch, with reductions of 60% and 31% respectively, compared to the standard net. However, the effectiveness of square mesh codend was considered to be limited by the maximum size of the square meshes which would provide too small an exit for large snakes (Courtney et al. 2010). Milton and colleagues (2009) found that the commonly used Fisheye BRD also had good exclusion (43% reduction in bycatch by weight) when placed at a distance of 66 meshes from the codend. Where sea snake mortality is high (eg area or sector related), more recent studies have suggested that the device should be placed closer to the codend, that is, 50 meshes (Courtney et al. 2010).
As part of the CMO program, tests undertaken on the Popeye Fishbox BRD, conducted by AFMA in the NPF in the Gulf of Carpentaria, reported an 87% reduction in the catch rate of sea snakes when the device was installed 70 meshes from the codend, with no significant effect on prawn catch rates (Raudzens 2007). However, repositioning the device to 100 meshes from the codend lowered the exclusion rate of bycatch of non-targeted species, thus making it less effective for sea snakes. Brewer and colleagues (2006) similarly found that there was no decrease in sea snake bycatch in the NPF when the BRD was placed at a distance of 120 meshes from the codend (i.e. maximum allowable distance under Australian law).
As shown from the above findings, the distance of the BRD from the codend significantly affects its ability to exclude bycatch of non-targeted species including sea snakes. Even if the most effective BRD is implemented, its performance will be greatly compromised unless an appropriate maximum distance from the drawstring of the codend is also specified (Courtney et al. 2010).
Additional factors that will reduce bycatch of sea snakes include the detection of reduced water flow and the length of hauls (Milton et al. 2009; Wassenberg et al. 2001). For a BRD to be effective, it must also enable the sea snakes to detect the reduced flow posterior to the device (Milton et al. 2009). When tested, the Fishbox BRD was found to have a relatively large region of reduced flow posterior to the device (Heales et al. 2008). The length of hauls has been found to also impact bycatch rates, with shorter hauls reducing the volume of bycatch which in turn increase the survival chances of sea snakes (Milton et al. 2009; Wassenberg et al. 2001).
Marine bioregional plans have been developed for four of Australia's marine regions - South-west, North-west, North and Temperate East. Marine Bioregional Plans will help improve the way decisions are made under the EPBC Act, particularly in relation to the protection of marine biodiversity and the sustainable use of our oceans and their resources by our marine-based industries. Marine Bioregional Plans improve our understanding of Australia's oceans by presenting a consolidated picture of the biophysical characteristics and diversity of marine life. They describe the marine environment and conservation values of each marine region, set out broad biodiversity objectives, identify regional priorities and outline strategies and actions to address these priorities. Click here for more information about marine bioregional plans.
The North-western Mangrove Seasnake has been identified as a conservation value in the North-west (DSEWPaC 2012y) Marine Region. The "species group report card - marine reptiles" for the North-west (DSEWPaC 2012y) Marine Region provides additional information.
No threats data available.
Brewer, D., D. Heales, D. Milton, Q. Dell, G. Fry, B. Venables & P. Jones (2006). The impact of turtle excluder devices and bycatch reduction devices on diverse tropical marine communites in Australia's northern prawn trawl fishery. Fisheries Research. 81:176-188.
Brewer, D., N. Rawlinson, S. Eayres & C. Burridge (1998). An assessment of bycatch reduction devices in a tropical Australian prawn trawl fishery. Fisheries Research. 36:195-215.
Cogger, H.G. (1996). Reptiles and Amphibians of Australia. Chatswood, NSW: Reed Books.
Cogger, H.G. (2000). Reptiles and Amphibians of Australia - 6th edition. Sydney, NSW: Reed New Holland.
Courtney, A., B. Schemel, R. Wallace, M. Campbell, D. Mayer & B. Young (2010). Reducing the impact of Queensland's trawl fisheries on protected sea snakes. Department of Employment, Economic Development and Innovation, Queensland Government.
Ehmann, H. (1992b). Reptiles. In: Strahan, R., ed. Encyclopedia of Australian Animals. Sydney: Angus & Robertson.
Guinea, M.L (in press). A technique for catching and restraining sea snakes. Herpetological Review.
Guinea, M.L. & S.D. Whiting (2005). Insights into the distribution and abundance of sea snakes at Ashmore Reef. The Beagle (Supplement 1). Page(s) 199-206.
Heales, D., R. Gregor, J. Wakeford, Y. Yarrow et al (2008). Effective reduction of diverse fish and sea snake bycatch in a tropical prawn trawl fishery using the Yarrow Fisheye Bycatch Reduction Device. Fisheries Research. 89:76-83.
Heatwole, H. (1975). Sea snakes of the Gulf of Carpentaria. In: Dunson, W.A., ed. The Biology of Sea Snakes. Page(s) 143 -149. Baltimore, University Park Press.
Heatwole, H. (1999). Sea Snakes. In: Australian Natural History Series. Page(s) 148. Sydney, NSW: UNSW Press.
Limpus, C.J. (1975). Coastal sea snakes of subtropical Queensland waters (23° to 28° South Latitude). In: Dunson, W. A., ed. The Biology of Sea Snakes. Page(s) 173-182. Baltimore: University Park Press.
Marsh, H., P.J. Corkeron, C.J. Limpus, P.D. Shaughnessy & T.M. Ward (1993). Conserving marine mammals and reptiles in Australia and Oceania. In: C. Moritz & J. Kikkawa, eds. Conservation Biology in Australia and Oceania. Page(s) 225-44. Chipping Norton, NSW: Surrey Beatty & Sons.
Milton, D., G. Fry & Q. Dell (2009). Reducing impacts of trawling on protected sea snakes: by-catch reduction devices improve escapement and survival. Marine and Freshwater Research. 60:824-832.
Milton, D., S. Zhou, G. Fry & Q. Dell (2008). Risk assessment and mitigation for sea snakes caught in the Northern Prawn Fishery. Fisheries Research and Development Conservation Corporation and CSIRO Marine and Atmospheric Research, Cleveland.
Milton, D.A. & G. Fry (2002). Assessment and improvement of BRDs and TEDs in the NPF: a co-operative approach by fishers, scientists, fisheries technologists, economists and conservationists. Fisheries Research and Development Corporation and CSIRO Marine Research. Cleveland, Queensland: CSIRO Marine Research.
Raudzens, E (2006). At sea testing of 'Popeye's Fishbox' bycatch reduction device onboard the FV Adelaide Pearl for approval in Australia's Northern prawn Fishery. [Online]. Available from: http://www.afma.gov.au/wp-content/uploads/2010/07/popeyebrdreport.pdf.
Wassenberg, T.J., D.A. Milton & C.Y. Burridge (2001). Survival rates of sea snakes caught by demersal trawlers in northern and eastern Australia. Biological Conservation. 100:271-280.
This database is designed to provide statutory, biological and ecological information on species and ecological communities, migratory species, marine species, and species and species products subject to international trade and commercial use protected under the Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act). It has been compiled from a range of sources including listing advice, recovery plans, published literature and individual experts. While reasonable efforts have been made to ensure the accuracy of the information, no guarantee is given, nor responsibility taken, by the Commonwealth for its accuracy, currency or completeness. The Commonwealth does not accept any responsibility for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the information contained in this database. The information contained in this database does not necessarily represent the views of the Commonwealth. This database is not intended to be a complete source of information on the matters it deals with. Individuals and organisations should consider all the available information, including that available from other sources, in deciding whether there is a need to make a referral or apply for a permit or exemption under the EPBC Act.
Citation: Department of the Environment (2014). Ephalophis greyi in Species Profile and Threats Database, Department of the Environment, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed Fri, 25 Apr 2014 19:10:33 +1000.