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Threats

In many parts of the world and in India, sea turtle populations are affected by a wide variety of threats. Even under natural conditions, survival rates are low, and eggs and hatchlings are predated by small carnivorous mammals, birds, lizards and crabs. Once they are in the sea, a variety of predators plague them through their immature stages. Only large sharks, perhaps killer whales and humans predate adults. At a few sites nesting turtles may be killed by large predators such as jaguars and tigers.

Human induced threats are increasingly problematic for turtle populations. These threats can be broadly classified into direct and indirect threats.

Direct threats:

Threat: Incidental catch in mechanised fisheries

Impacts: Sea turtle mortality occurs primarily in gill nets and in trawl nets by drowning. Although sea turtles are capable of staying submerged for half hour or more, the stress of being trapped for many hours in gill and trawl nets usually results in drowning. Some turtles trapped in trawl nets are not dead, but comatose, and if they are thrown back into the water immediately, they are likely to die. On the other hand, if they are kept on board the ship, they may recover.

Mitigation: Declaring no fishing zones, imposing seasonal fishing bans, encouraging use of Turtle Excluder Devices.

Threat: Consumption of adults – not very common in most parts of the Indian coastline

Mitigation: Involving the local community in conservation efforts by making them aware of the importance and benefits of such efforts, thereby reducing their dependence on adult sea turtles as sources of food or income. It is important that the initiation of such programmes should take into consideration the socio-cultural dynamic of the area to ensure that the programme doesn’t negatively affect the socio-economic structure of the community. Inclusion of the resource user community’s interests is likely to increase the chances of their supporting the programme.

Threat: Egg depredation by feral animals and humans

Mitigation: Elimination of predators: This option should only be exercised with semi-domestic, feral, introduced and widespread species. Education and awareness among local communities and information about existing wildlife protection laws.

Indirect threats

Nearshore waters – where turtles come to breed and feed – are often subject to heavy use by humans in terms of marine fishing, aquaculture, coastal tourism and other recreational activities. These coastal zones are also susceptible to indirect pollution from industrial or agricultural run-off. These activities impact sea turtles during various crucial stages of their life cycle.

Threat: Loss of marine habitats (due to pollution, aquaculture, coastal tourism, etc.)

Pollution

Impacts: Impacts of pollution on sea turtles have been less severe than on other marine and coastal flora and fauna, although accidental ingestion of plastics has been documented to indirectly cause death due to poisoning or starvation because of the inability to swallow food due to the blockage of the food passage by these materials. Further, changes in water temperature and quality results in changes in their offshore breeding congregation locations. Changes in salinity profile and levels of organic and inorganic pollutants in the vicinity of mass nesting sites will impact adults and hatchlings.

 

Mitigation:

Options to minimise pollution:

• Prohibition of discharge of crude oil, pesticides, heavy waters, heavy metals and other poisonous effluents to estuaries and coastal areas and near turtle nesting beaches.
• Prohibition of discarding of fishing lines, nets, plastic bags other trash into the water or on the beach which results in ghost fishing and incidental mortality of sea turtles.
• Organised cleaning up of the beach and nearshore waters by local forest and fisheries departments and other governmental agencies in collaboration with non-governmental organisations, coastal communities, and school and college students. This should particularly be taken up prior to the breeding season of sea turtles in an attempt to clean up the habitat as well as to educate people about marine turtles.

Aquaculture

Impacts: Intensive and uncontrolled aquaculture expansions along the coast have resulted in the loss of sea turtle nesting and foraging habitats. In addition, aquaculture farms along the coast have become a major source of light pollution for marine turtles.

 

Mitigation:

Guidelines for ecofriendly aquaculture:

• Delineation of proper aquaculture zones away from important sea turtle nesting sites.
• Total ban of prawn seed collection from the immediate offshore waters using any kind of scoop net.
• Ban on the use of bright illumination that spreads light to the seashore during the nesting and hatching seasons
• Total prohibition on the release of chemicals and effluents from aquaculture farms and hatcheries into the marine and coastal riverine systems.

 

Coastal tourism:

Impacts: Physical alteration and loss of nesting beaches from tourism infrastructure, including removal of vegetation, sand, etc., speedboat movement which may cause physical injuries to adults (propeller inflicted), damage reefs, and release pollutants, littering of the beach by tourists, disturbance to nesting females, etc.

Mitigation:

Guidelines for ecofriendly tourism:

• Seasonal closure of coastal tourism activities in nesting beaches and lagoons should be adopted.
• Tourism infrastructure development should only be permitted beyond 200 meters from the high tide line or on the landward slope of the sand dune berm rather than the seaward slope.
• All illumination must be made sea turtle friendly. Green ratings and punish and award system can be adopted to encourage turtle friendly infrastructure.
• A total ban on joy rides on nesting beaches using animals or heavy vehicles should be enforced.
• Beach leveling and removal of natural vegetation should only be permitted in consultation with sea turtle biologists or coastal zone management authorities.
• Controlled foot traffic on sea turtle nesting beaches during daytime to avoid compaction of sand, and during nighttime to avoid disturbing nesting turtles, other than those areas where tourists are taken under well organised sea turtle watch programmes.
• The tourism department, beach resorts and other beneficiaries of beach tourism can involve local communities and schools to adopt a particular sea turtle nesting beach and demonstrate turtle friendly practices.

 

Threat: Loss of nesting beaches (due to erosion, sand mining, beach armouring, pollution, exotic plantations, etc.)

Sand mining

Impacts: Coastal sand mining can change the entire beach geomorphology and restoration of the beach often takes years resulting in loss of available habitat for marine flora, fauna and sea turtles. The immediate deleterious impact of beach sand mining on sea turtles is to uncover and destroy nests. Raking can also leave ruts and ridges that disrupt hatchlings’ sea finding behaviour.

Mitigation:

The Government of India, in 1991, issued a major notification under the Environmental Protection Act, 1986, framing rules and regulations (Coastal Regulation Zone (CRZ) Rules) for various developmental activities along the coast. The maritime states are in the process of preparing CRZ maps, which clearly delineate fragile, sensitive and ecologically important nesting beaches of rare and endangered fauna and such identified zones are not to be subjected to any form of sand mining. In this context, before taking up any coastal sand mining activity, the concerned agencies must ensure that the targeted areas are not important habitats of any marine fauna.

These sensitive coastal stretches need to be identified, properly marked with site boards and labels and removal of sand from such zones or primary dunes should be completely prohibited.

Even where sand mining may be allowed, the actual mining must be preceded by proper impact assessment studies conducted by the development agencies in collaboration with the coastal resource management authorities including environment, forest and wildlife agencies.

Beach armouring

Impacts:

There are four broad consequences to the beach/dune system that can result from coastal armouring.

 

• Coastal armouring structures cause reflection in wave energy, which can increase erosion seaward of these structures.
• The intensity of long shore currents can be increased, moving sand away from the site more rapidly and in greater quantities.
• The natural exchange of sand between the dune and the beach is prevented; the wave energy is concentrated at the end of armoring structures, which can exacerbate erosion at an adjacent, unarmoured beach.
• These structures physically block female turtles from reaching suitable nesting sites, or the presence of these structures may be aversive to nesting females. These structures may also disrupt sea finding of hatchlings once they emerge.

 

Mitigation:

All important sea turtle nesting beaches of moderate intensity must be identified and should be free from beach armouring as sea turtles normally prefer gentle sloping seaward sand dunes rather than beaches which are subject to regular erosion.

 

Beach changes must be measured and monitored on a regular basis. This information should be used by planning agencies and others to reduce the problems caused by coastal erosion and to conserve and effectively manage coastal development.

Exotic plantations

Impacts:

Exotic coastal plantations have proved to be detrimental to the nesting of sea turtles in more ways than one.

 

• Plantation of exotic beach vegetation drastically alters the beach profile and may often be a deterrent for sea turtle nesting.
• Since all coastal plantations are taken up on either side of the sand dune berm, there is significant loss of sea turtle nesting habitat between the high tide line and the berm on the seaward side.
• Alien vegetation such as Casuarina with its superficial root growth and thick litter fall renders the beach unsuitable for turtles to nest.
• Dense Casuarina and other plantations cause excessive shading of the nesting beach. Nests laid in shaded areas are subject to lower incubation temperature, which alters the natural sex ratio of turtle hatchlings, producing more males.
• Plantation of exotic vegetation on the beach also affects the natural beach formation process.
• Dense vegetation on the coastal sand dunes provides shelter for both natural (jackal, hyena, monitor lizard, wild pig, etc.) and subsidised predators (dogs, pigs, etc.) to breed and add additional predation pressure on nesting females, eggs and hatchlings.

 

Mitigation:

The biological and ecological significance of the beach is often overlooked while undertaking developmental activities or afforestation programmes. The following guidelines are therefore suggested for ecofriendly revegetation of the coastal sand dunes.

 

• As a policy, no exotic species should be planted in CRZ areas to prevent unknown ecological impacts.
• Environmental and ecological impact assessment studies must be conducted before taking up any afforestation programmes along the coast, with provisions set up to evaluate any post-project impacts on sea turtles.
• Plantation of exotic vegetation should be clearly avoided on beaches that are known to be sea turtle nesting grounds.
• Apart from the high priority sea turtle nesting beaches where no plantation should be taken up, in sporadic sea turtle nesting areas, plantations should be carried out beyond 200 m from high tide line (HTL) and on the landward side slope from the berm thereby setting aside enough space for sea turtles to nest.
• In historically known sea turtle nesting sites, alien and exotic plantations should be gradually removed to restore the nesting beach to its former state.

 

Threat: Lighting (disorientation of both adults and hatchlings, mainly the latter)

Impacts: Artificial illumination on nesting beaches impacts adult sea turtles by disrupting nest site selection, abandonment of nesting behaviour, disruption of sea finding ability and disorientation following unsuccessful nesting. Sea turtle hatchlings orient themselves towards the sea as soon as they emerge from the nest. Under natural conditions, the hatchlings recognise the direction of the ocean almost exclusively by visual stimuli, detecting the brightness of the open seaward horizon, due to the reflection of stars and moonlight on water. Sand dunes and vegetation along the nesting beach also help create a darker horizon on the landward side. However, on beaches where artificial lighting is clearly visible, the hatchlings’ journey to the sea is disrupted. Hatchling sea turtles emerging from nests at night are strongly attracted to visible light sources along the beach. Consequently, hatchlings move toward the source of artificial illumination and away from the ocean. They thus fail to find their way to the sea, and succumb to predators or exhaustion or dehydrate in the morning sun.

Mitigation:

Guidelines for coastal illumination:

Artificial illumination along important sea turtle nesting beaches during the nesting season must be turned off (depending on the species, the peak nesting season at any particular location usually does not exceed three months of the year).

 

• The number of lights near sporadic and secondary nesting beaches must be reduced to the minimum necessary and switched off during peak nesting nights.
• Illumination reaching the nesting beach can be reduced by lowering, shielding, and redirecting light sources onto immediate land rather than towards the sea. Even the glow on the horizon can affect sea turtles. Low mounted lights are better than lights that shine upwards from a high pole.
• An easy means to reduce the influence of light on turtle beaches is to screen them on the seaward side. This can be done by applying dark tinting to windows visible to the beach and by drawing curtains after the dark to shield lights from going to the seashore. Additionally, a vegetation wall or green fence can be created to block light from reaching the sea.
• Care in placement and orientation of light fittings on coastal buildings and infrastructure will considerably reduce the impact of direct and scattered lighting on turtle beaches. This can easily be done by orienting lights towards land or by directing lights downwards and by using lamp shades that do not allow lights to reach the beach.
• Studies have shown that fluorescent, mercury vapour, high pressure sodium vapor, metal halide and white incandescent lighting disorient sea turtles the most. Further studies need to test which lights affect sea turtles the least (and this may be species specific). For loggerheads, low pressure sodium vapor lights (not to be confused with high pressure sodium vapor) that emit a pure yellow light seems to work best. Similar studies need to be carried out for olive ridleys which nest along much of the Indian coast and are most affected by lighting problems.