The predators represent the main natural threats for marine turtles. Feral dogs, water monitors, land monitors, jackals, wild boars, mongooses, several species of ants and crabs can be considered as natural predators for marine turtle eggs and hatchlings on nesting beaches. Killer whales / Orca whales, Sharks and other reef fishes and sea birds prey on hatchlings in the sea. Sometimes harsh weather conditions such as storms, tornados, draughts and El Nino phenomenon can cause damages to the laid turtle nests.
Man made Threats
Today marine turtles are in great danger mostly due to the activities of human beings. Some of the man made threats are briefly described below.
• Killing for Their Meat
Marine turtles are killed for their meat in many countries. In Sri Lanka, slaughter of marine turtles for meat is a traditional practice in many coastal areas. Slaughter of nesting adult females directly effects the reduction of the turtle population. Live turtles entangled in fishing gears are also slaughtered by for flesh by the fishermen.
• Killing for Shell
The highly endangered Hawksbill turtles have been killed in many parts of the world for its beautiful shell or carapace to provide raw material for the "tortoise shell" trade (Photo no. 29). When scutes are removed from the shell, the turtle eventually dies. Synthetic fibers with similar color patterns are now available to replace the tortoiseshell raw materials for the good sake of hawksbill turtles.
• Egg Collection
One of the most widespread forms of marine turtle exploitation is the illegal poaching of turtle eggs (Photo no. 30). As female turtles come ashore to lay their eggs this makes a easy prey for egg collectors who take the eggs and sell them. All marine turtle nests on Sri Lankan beaches are robbed of their eggs except in places where conservation programmes are implemented. The eggs are either sold at markets for consumption or to turtle hatcheries.
Below: An Egg Poacher steals an entire clutch from a nesting green turtle as the eggs are dropped into the egg chamber.
• Turtle by-catch
Large number of marine turtles becomes victims of the modern fishing gear. Well over 5000 turtles are entangled annually in floating and bottom set gill nets in Sri Lanka. Shrimp trawling and fishing hooks with baits cause serious damages to marine turtles in other parts of the world.
Photo by: Priyankara Sedawatta.
• Non-Scientific turtle hatchery practices
Once in the sea the hatchlings swim constantly swim against the direction of the waves for a period of 24-48 hours without feeding (Juvenile frenzy). During this period the hatchlings derive their nutrition from an internal, residual yolk, an energy supply that is exhausted at the end of the frenzy. Many hatcheries in Sri Lanka retain hatchling turtles in concrete tanks for at least three days as a practice. When hatchlings are kept in tanks for a longer period (e.g. 3-4 days), the hatchlings spend the first one or two days constantly swimming around the tanks without feeding. On the third day the hatchlings' behavior changes to feeding behavior and because they are kept in tanks with many of their siblings, they begin to bite at each other. Some of the hatchlings receive injuries as a result, which often become infected by bacteria and fungi, thus lowering the hatchlings' chances of survival .
• Habitat Destruction:
Important marine turtle habitats such as coral reefs, sea grass beds, mangroves, sand dunes and beach vegetation are been degraded by man in many parts of the world due to over exploitation. Some of the major human activities that cause marine turtle habitat destruction and alteration are briefly described below.
• Coral mining
Coral reefs provide an important feeding and relaxing habitat for marine turtle as well as a vital protective barrier for the turtles' nesting beaches from sea erosion. Sri Lanka's coral reefs are being destroyed by unsustainable harvesting.
• Beach erosion
The removal of corals from reefs and sand from the beach increases the rate of beach erosion. The result will be the destruction of nesting habitats of marine turtles.
• Beach front development
Large hotels and restaurants adjacent to the beach create a lot of noise and light. This may disturb nesting female turtles. When the hatchlings emerge they can be disorientated by the lights and head for the hotels instead of the sea.
• Marine pollution
Marine pollution claims the lives of many marine turtles. Leatherback turtles feed on jellyfish and they mistake plastic bags floating in the water for jellyfish. As the plastic bag block the turtle's gut the animals starve to death.
In addition, tumor like disease called "Fibropapilloma" is a cause for many marine turtle deaths. It is believed that marine pollutants cause this disease. However Fibropapilloma is not seen among the turtle populations in Sri Lanka at the moment.