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 Temperate East Marine Region (Department of Sustainability, Environment, Water, Population and Communities (DSEWPaC), 2012aa) [Admin Guideline].
Marine bioregional plan for the North Marine Region (Department of Sustainability, Environment, Water, Population and Communities (DSEWPaC), 2012x) [Admin Guideline].
Marine bioregional plan for the North-west Marine Region (Department of Sustainability, Environment, Water, Population and Communities (DSEWPaC), 2012y) [Admin Guideline].
Sea snakes - A Vulnerability Assessment for the Great Barrier Reef (Great Barrier Reef Marine Park Authority (GBRMPA), 2011f) [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||Hydrophis ornatus |
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 Ornate Seasnake, Hydrophis ornatus, under Australian Government legislation, is as follows:
National: Listed as a marine species under the Environment Protection and Biodiversity Protection Act 1999.
Scientific name: Hydrophis ornatus
Common name: Ornate Seasnake
In Australia, specimens of the Ornate Seasnake have previously been referred to as the subspecies Hydrophis ocellatus (Smith 1926). However, other studies have raised doubts as to the status of this subspecies (Cogger 1996).
The Ornate Seasnake is a moderate to heavily built snake which is relatively uniform along its length. Individuals are grey or blue grey above, with 3060 broad black bands and laterally, a series of pale ocelli (circles or ellipses) with dark borders. The head shields are large and regular. Body scales are imbricate (overlapping) in 3959 rows at the mid-body. The ventral scales are about twice as broad as adjacent body scales and number 240340. The Ornate Seasnake grows to an average length of one metre (Cogger 1996).
The Ornate Seasnake occurs in tropical northern Western Australia, the Northern Territory and northern Queensland. The species sometimes occurs further south in summer, extending its range as far as Tasmania (Cogger 1996).
The species is widely distributed throughout tropical coastal areas of northern Australia, southern Papua New Guinea, New Caledonia, Indonesia, the Philippines and the South China Sea (Cogger 1996; Ineich & Rasmussen 1997).
The Ornate Seasnake occurs in a variety of habitats, including clear water near coral reefs and turbid (muddy) water in estuaries (Cogger 1996).
The species has been captured throughout the Gulf of Carpentaria (Milton and Fry 2002; Ward 2000), particularly at depths of 2150 m (Ward 2000).
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 Ornate Seasnake, like most sea snakes, is viviparous, that is giving birth to live young (Cogger 2000). In addition, 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).
More specifically, in northern Australia, the mean number of young for females of the species, is six (with a standard error of 0.5, in a sample of 37) (Fry et al. 2001). The length of gestation in northern Australia is around six to seven months, and births are in September. Females appear to reproduce every year (Fry et al. 2001). Data from Thailand indicates brood sizes range from 14 (Rasmussen 1989).
In Australia, the Ornate Seasnake eats benthic (ocean floor dwelling) and demersal (occurring just above the benthic zone) fish. Benthic species include Apogon ellioti and A. poecilopteris (Apogonidae), Sirembo imberbis, and Yongeichthys nebulosus. Demersal species include members of the genus Mullidae, Nemipterus nematopus (Nemipteridae) and Priacanthus tayenus (Priacanthidae) (Fry et al. 2001).
Data from Thailand indicates that the Ornate Seasnake preys on species from at least six families of fish. The fish families recorded from the stomachs of the Ornate Seasnake from Thailand include, Apogonidae, Holocentridae, Labridae, Leiognathidae, Nemipteridae and Scaridae (Rasmussen 1989; Voris & Voris 1983).
The Ornate Seasnake catches fish that are generally free swimming and occur in habitats that are close to the coral reef, including areas of sand adjacent to reefs (Rasmussen 1989; Voris & Voris 1983). This species is also known to eat benthic fish that are regularly discarded from prawn trawling (Milton 2001).
In Australia, the Ornate Seasnake ranges further south during summer, extending its range to Tasmania (it is one of only three species of seasnakes to do so) (Cogger 1996).
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).
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).
The Ornate Seasnake is among the most commonly captured species of sea snake in many areas where trawling occurs. This species comprised 143% of bycatch during commercial and research trawling in northern Australia (Fry et al. 2001). Studies in the 1970s found that the Ornate Seasnake represented 66% of the sea snakes captured in north-west Australia, 36% in the Arafura Sea and 58% in the Timor Sea (Shuntov 1971). In the Gulf of Carpentaria and north-east Queensland, this species comprised only 12% of bycatch during research and prawn trawling (Redfield et al. 1978; Wassenberg et al. 1994). High percentages of Ornate Seasnakes were also captured on the northern Australian continental shelf in the mid-1990s: 31% during fish trawling (Ward 1996a), and 1517% during Banana and Tiger/Endeavour prawn trawling (Ward 1996b).
Wassenberg et al. (2001) reported that Ornate Seasnakes had the highest rates of mortality after trawling of any sea snakes tested: 18 of 85 captured during prawn trawling were dead when they were brought onto the trawler; and eight of 17 died during the four days that they were retained after capture.
Bycatch Reduction Overview
Milton and Fry (2002) found that the Bycatch Reduction Device (BRD) was more effective at reducing the number of sea snakes captured during prawn trawling than either the Turtle Excluder Device (TED), or a combination of both a BRD (for example the Fisheye BRD) and a TED. BRDs are escape grids or openings designed to enable smaller animals to swim out of the net, and TEDs are hard grids placed in trawl nets to exclude turtles and other large animals. These devices have two functionalities. Firstly, the devices reduce the number of fish caught which decreases the weight of the catch, therefore, reducing the physical damage to sea snakes caught in the nets. Secondly, the devices enable any sea snake caught, to escape (Wassenberg et al. 2001).
Sixteen devices were tested during a 1998 study (Brewer et al. 1998). Brewer and colleagues (1998) found that the most effective BRDs, for most sea snakes, were the AusTED and Nordmore grids with square mesh windows. These devices reduced the rate of sea snake capture from one every second tow to one every four or five tows, thus, reducing sea snake bycatch by up to 50% (Milton et al. 2009). All other devices resulted in capture rates that were equal to, or slightly higher than, standard trawler net figures. The AusTED and Nordmore grids were found to be most effective when they were located within 50 meshes of the drawstrings and well within the maximum distance required by Australian law (120 meshes) (Milton et al. 2009). A mesh pertains to a square of line in the net, one mesh being equal to one square of netting.
Prawn Trawling Crew Member Programs
Prawn trawling is having a large negative impact on protected sea snake populations (Milton et al. 2008). In order to monitor the sea snakes in the bycatch, and their numbers, a Crew Member Observer (CMO) program was established in the Northern Prawn Fishery (NPF) in 2003. This program aims to (inexpensively) collect data on bycatch such as composition, catch rates and distribution during both NPF tiger and banana prawn fishing seasons. The initiative requires 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 20032005 seasons, 21 crew member observers on 17 vessels collected data from 7602 tiger and 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 their fishing activities (Milton et al. 2008).
Another CMO program (called the Crew Member Program or CMP) was brought into effect in the Queensland East Coast Trawl Fishery (QECTF) during July 2005October 2007 (Courtney et al. 2010). As part of this program, bycatch data were collected from fisheries such as the shallow and deepwater eastern king prawn, scallop, banana prawn, redspot king prawn, North Queensland tiger/endeavour prawn, black tiger prawn broodstock collection, beam trawl and stout whiting trawl fisheries. During the study from 8289 trawls, information on bycatch rates, composition and mortality was collected. A total of 3910 sea snakes were captured from the 8289 trawls. Identification of the bycatch was made using digital photos taken by trained crew members. The study found that the highest catch of sea snakes was in redspot king prawn fishery, due to an overlap with sea snake habitat (Courtney et al. 2010).
Current Bycatch Reduction Methods and Effectiveness
Brewer and colleagues (2006) 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 drawstring. This distance is the maximum allowable distance under Australian law (Milton et al. 2009). Fishers installing their BRDs closer to the codend, (that is, at approximately 70 meshes from the drawstring) found that bycatch of sea snakes and fish was substantially reduced with negligible prawn loss (Heales et al. 2008).
During the CMO program, CMOs and scientific observers found that the 'popeye' Fishbox BRD showed the greatest reduction (87%) in sea snake catch rates and overall bycatch by weight (48%) when compared to other BRD types (Milton et al. 2009; Raudzens 2006). In addition, the commonly used Fisheye BRD was also found to have good exclusion (43% reduction in bycatch by weight) when placed at a distance of 66 meshes from the drawstring (Milton et al. 2009). Where sea snake mortality is high, more recent studies have suggested that the device should be placed closer to the drawstring, that is, 50 meshes (Courtney et al. 2010)
It has been suggested that, for a BRD to be effective, it must 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 position of the BRD, forward of the codend, has a large effect on the escape of bycatch (mainly fish) (Milton et al. 2009). This position, together with the total catch weight, has previously been found to have the largest effect on the survival of sea snakes (Wassenberg et al. 2001). In addition, the length of hauls has been found to impact bycatch rates, with shorter hauls reducing the volume of bycatch (Milton et al. 2009; Wassenberg et al. 2001). Therefore, the placement and the design of the BRD and the length of hauls are clearly areas of future research and management solutions to reduce impacts on sea snake populations.
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 Ornate Seasnake has been identified as a conservation value in the North-west (DSEWPaC 2012y), North (DSEWPaC 2012x) and Temperate East (DSEWPaC 2012aa) marine regions. The "species group report card - marine reptiles" for the North-west (DSEWPaC 2012y), North (DSEWPaC 2012x) and Temperate East (DSEWPaC 2012aa) marine regions provide 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.
Fry, G.C., A. Milton & T.J. Wassenberg (2001). The reproductive biology and diet of sea snake bycatch of prawn trawling in northern Australia: characteristics important for assessing the impacts on populations. Pacific Conservation Biology. 7:55-73.
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.
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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.
Ineich, I. & A.R. Rasmussen (1997). Sea snakes from New Caledonia and the Loyalty Islands (Elapidae, Laticaudinae and Hydrophiinae). Zoosystema. 19 (2-3):185-192.
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. (2001). Assessing the susceptibility to fishing of populations of rare trawl bycatch: sea snakes caught by Australia's Northern Prawn Fishery. Biological Conservation. 101:281-290.
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.
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Redfield, J.A., J.C. Holmes & R.D. Holmes (1978). Sea snakes of the eastern Gulf of Carpentaria. Australian Journal of Marine and Freshwater Research. 29:325-334.
Shuntov, V.P. (1971). Sea snakes of the North Australian Shelf. Ekologiya. 4:65-72.
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Voris, H.K.& H.H. Voris (1983). Feeding strategies in marine snakes: an analysis of evolutionary, morphological, behavioural and ecological relationships. American Zoologist. 23(2):411-425.
Ward, T.M. (1996a). Sea snake bycatch of fish trawlers on the Northern Australian continental shelf. Marine and Freshwater Research. 47:625-630.
Ward, T.M. (1996b). 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 Freshwater Research. 51:155-164.
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.
Wassenberg, T.J., J.P. Salini, H. Heatwole & J.D. Kerr (1994). Incidental capture of sea-snakes (Hydrophiidae) by prawn trawlers in the Gulf of Carpentaria, Australia. Australian Journal of Marine and Freshwater Research. 45:429-43.
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 (2013). Hydrophis ornatus in Species Profile and Threats Database, Department of the Environment, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed Fri, 13 Dec 2013 06:52:54 +1100.