Sea Snakes

Condition

Diversity, distribution and population status

The waters of northern Australia support a wide diversity of sea snakes with 31 species recorded from the area, approximately half of which are endemic to the region. Seventeen species of sea snakes have been reported from the Great Barrier Reef, but none are endemic to the Great Barrier Reef World Heritage Area. Sea snakes occur in a wide variety of habitats with some species found mostly on coral reefs, whereas others are found over sandy and muddy areas of seabed. Many species are specialist feeders that are restricted to the specific habitats used by their prey. Research conducted in the Gulf of Carpentaria suggests that some species use shallow, inshore habitats as nursery grounds.

Seventeen species of sea snakes have been reported from the Great Barrier Reef but the status of their populations is not known.

The distribution of sea snake species is highly variable and thought to be influenced by seasonal factors. There are also records of sea snakes forming mating or breeding aggregations. However, there have been few studies conducted on sea snakes in the Great Barrier Reef and the status and distribution of populations is unknown. Nevertheless, sea snakes are known to be relatively long-lived animals with low reproductive outputs. This means that as the number of breeding adults in a population declines, the number of young replenishing the population may also decline rapidly. This also means that populations may take a long time to recover once depleted. Collectively, these traits make sea snakes more vulnerable to pressures than shorter lived species that produce plenty of young.

Conservation status

None of the sea snake species found in the Great Barrier Reef are listed in the 2002 Red List of Threatened Speciesof the World Conservation Union (IUCN). However, sea snakes are a listed marine species under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999, meaning that it is an offence to kill, injure, take, trade, keep or move sea snakes without a specific permit. The lack of information about the population status of sea snakes in the Great Barrier Reef is of concern to Reef managers, especially since their long life spans and low reproductive outputs make them especially vulnerable to impacts.

Pressure

The limited information available suggests that the main pressure on sea snakes is incidental catch in trawl nets (bycatch). However, pressures that affect habitats such as coral reefs and benthic communities may have indirect effects on sea snakes. Disturbance from vessel noise and boat strike have also been listed as pressures on sea snakes in Northern Australia but no scientific studies have been conducted on the effects of these activities.

Pressure: incidental catch

The limited information available suggests that the main pressure on sea snakes in the Great Barrier Reef is incidental catch in trawl nets.

In the Great Barrier Reef, sea snakes that roam over the seabed away from coral reefs may be accidentally caught in trawl nets. However, most of the research about sea snake bycatch in trawl nets has been conducted in the Northern Prawn Fishery that operates in the Gulf of Carpentaria and Northern Australia. These studies have shown that sea snake bycatch varies between different areas, depth ranges and seasons and that some species are more susceptible to capture than others. The survival rate of captured sea snakes also differs between species, but survival is also dependent on the duration of the trawl and the weight of the catch contained in the net. Research has also shown that female sea snakes are caught more often than males, and that mature snakes are caught more often than juveniles. Overall, it is thought that up to 33% of sea snakes caught in trawl nets die either by drowning or from injuries sustained during capture. The species most at risk from trawling are those that are most easily captured, are rare, and/or have lower capacities to recover. Trawling in areas where sea snakes aggregate can significantly increase the incidental catch of these animals and could have significant impacts on sea snake populations.

Estimates from the Northern Prawn Fishery indicate that in 1991, between 30,000 and 67,000 sea snakes were killed as a result of commercial prawn trawling, although the actual impact of this mortality on the populations is not known. Unfortunately, there are no figures available for the number of sea snakes killed by trawling in Great Barrier Reef and comparisons with the Northern Prawn Fishery are complicated as the trawl fishers in the Great Barrier Reef generally use shorter trawl “shots” than fishers in the Northern Prawn Fishery. Nevertheless, it is recognised that sea snakes are taken as bycatch in the Great Barrier Reef, and that the impact of trawling on Great Barrier Reef sea snake populations requires further attention. More information about trawling in the Great Barrier Reef can be found in Environmental status – inter-reefal and lagoonal benthos and Management status – fisheries.

Pressure: habitat degradation

Sea snakes are protected under the Environment Biodiversity and Conservation Act (1999) and the GBRMP Zoning Plan (2003). However, more information is needed to assess management priorities for these animals.

The sea snake species associated with coral reef habitats are thought to be more or less free from direct human pressures. However, pressures that affect sea snake habitats such as coral reefs are likely to indirectly affect the sea snake populations that rely on these habitats. Coral reefs, seagrass meadows and benthic habitats may be affected by large-scale pressures such as declining water quality and climate change, as well as localised pressures such as anchor damage and dredging. In inter-reefal and lagoonal areas, repeated bottom trawling may remove up to 90% of the seabed biomass, effectively removing benthic habitats that may be important sources of food or shelter for sea snakes.

Nevertheless, without information on the ecology and habitat use of sea snakes, or the status of their populations, the extent to which habitat degradation could potentially affect sea snake populations is unknown and more research in this area is required. The condition of these habitats and the pressures acting on them are complex issues in their own right, and are considered in detail in other chapters. For more information about known sea snake habitats, see: 

• Environmental status – corals
• Environmental status – inter-reefal and lagoonal benthos
• Environmental status - seagrasses

Response

There are currently few management responses specifically directed at sea snake conservation in the Great Barrier Reef. The lack of information on sea snake populations presents a challenge to Reef managers in identifying the most appropriate management response. Nevertheless, given the vulnerability of some sea snake species due to their life history traits and the potential for sea snakes to be caught in trawl nets, the most appropriate management response is to minimise the pressure from known human activities while initiating research programs to inform a long term management approach. In recognition of their vulnerability, sea snakes are listed marine species under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act 1999)meaning that it is an offence to kill, injure, take, trade, keep or move sea snakes in Commonwealth waters without a specific permit. In the Great Barrier Reef, sea snakes are also protected under the Great Barrier Reef Marine Park Zoning Plan 2003. Research on the population traits and gene flow between sea snakes in different regions of the Great Barrier Reef is currently being conducted through the Cooperative Research Centre for Reef Research, however more information on the abundance, population dynamics, distribution and impacts of human activities is required to comprehensively assess the pressure, risks and management priorities for sea snakes on the Great Barrier Reef.

Response: incidental catch

Concern about the long-term sustainability of the trawl fishery and impacts on bycatch species, including sea snakes, has led to the introduction of new management arrangements for the fishery. In 2000, the East Coast Trawl Fishery Management Plan came into effect, under which the Bycatch Reduction Devices (BRD’s) became mandatory. The overall effectiveness of BRDs in reducing bycatch  (including sea snakes) in the Great Barrier Reef trawl fishery is still being assessed. From research conducted in the Northern Prawn Fishery in the Northern Territory, it appears that the square mesh net BRDs are the most successful of the BRD designs in allowing sea snakes to escape. However, these devices are not commonly used by trawlers in the Great Barrier Reef.  There have been concerns regarding the adoption of BRDs in the trawl fleet (see the Audit of the management of the Queensland East Coast Trawl Fishery in the Great Barrier Reef Marine Park) but the Queensland Department of Primary Industries and Fisheries has since amended the Trawl Plan to address these concerns (see Marine turtles, Response: reducing incidental catch).

Under the EPBC Act 1999, the Great Barrier Reef trawl fishery was assessed against the Commonwealth Government’s Guidelines for the Ecologically Sustainable Management of Fisheries. In December 2004, the trawl fishery was declared as an approved Wildlife Trade Operation (WTO) until December 2007. For more information on this assessment, see Marine turtles, Response: reducing incidental catch), and the Department of Environment and Heritage’s assessment report. Further information about the management of trawling in the GBRMP can be found in Environmental status – inter-reefal and lagoonal benthos and Management status – fisheries.

Response: habitat degradation

The Reef Water Quality protection Plan has been introduced to improve water quality on the Great Barrier Reef.

While the Great Barrier Reef has not experienced the level of habitat degradation evident in coastal and marine regions elsewhere in the world, the pressures on habitats within the Great Barrier Reef are increasing. The large-scale pressures most likely to affect sea snake habitats are declining water quality and climate change. In 2002, the Commonwealth Government and Queensland Government signed a Memorandum of Understanding to develop a Reef Water Quality Protection Plan aimed at halting and reverse declining water quality in the Great Barrier Reef within 10 years. The Reef Water Quality Protection Plan will be developed with regional Natural Resource Management bodies to ensure that water quality programs are appropriate for each region. For more information on water quality issues in the Great Barrier Reef see Environmental status – water quality.

Throughout the Great Barrier Reef, sea snake habitats such as coral reefs, seagrass meadows and benthic habitats in inter-reefal and lagoonal regions have been provided with increased protection under the new Great Barrier Reef Marine Park Zoning Plan 2003 that came into effect on 1 July 2004. The new zoning plan has increased the area of ‘no-take’ zones from less than 5% to approximately 33% of the Great Barrier Reef Marine Park and has been designed to provide adequate protection for the range of biodiversity found in the Great Barrier Reef. The new plan is also designed to preserve the ecological functions and maintain the biological connections between the different habitats of the Great Barrier Reef. In doing so, the new Zoning Plan will help to support species such as sea snakes that use the various habitats of the Great Barrier Reef, and increase the resilience of the entire Reef ecosystem to cope with multiple localised pressures and large scale pressures such as declining water quality and climate change.

Sea snake habitats are also affected by a wide range of specific and/or localised pressures, each of which is addressed by specific management responses. These specific pressures and responses are considered in detail in individual chapters and thus, are not considered further in this chapter. For more information on sea snake habitats such as coral reefs, seagrass meadows and benthic habitats in the inter-reefal and lagoonal regions, please refer to the following chapters:

• Environmental status – corals
• Environmental status – inter-reefal and lagoonal benthos
• Environmental status - seagrasses