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.
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.
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.)
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.
Options to minimise pollution:
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.
Guidelines for ecofriendly aquaculture:
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.
Guidelines for ecofriendly tourism:
Threat: Loss of nesting beaches (due to erosion, sand mining, beach armouring, pollution, exotic plantations, etc.)
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.
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.
There are four broad consequences to the beach/dune system that can result from coastal armouring.
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 coastal plantations have proved to be detrimental to the nesting of sea turtles in more ways than one.
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.
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.
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).