Turtles of the size range found on the Bermuda Platform have only one natural enemy sharks. Small post-hatchlings found out in the Sargasso Sea are threatened by a wider range of predators including fish and several species of birds. Eggs and hatchlings on nesting beaches face predation by ants, crabs, birds and dogs on land, and the hatchlings face a host of marine carnivores such as snappers, groupers, barracudas and sharks once they reach the sea. Nests are also lost to erosion of the nesting beach.
Learning from sea turtle necropsies.
Threats to sea turtles in Bermuda are documented by a Stranding Network at BAMZ that receives stranded turtles from the public in Bermuda. Some of these turtles can be saved and returned to the wild (see section on Rehabilitation). However, information on the cause of death of some of the animals that don’t survive can be gained during necropsies. Each year, as part of the Bermuda Turtle Project’s annual course, sea turtles that have died from a variety of causes are necropsied under the direction of Dr. Ian Walker, the Director of BAMZ. The examples discussed below have been observed during these necropsies.
Although sea turtles are strongly protected in Bermuda waters, they still experience many negative impacts from humans.
The sea turtles of Bermuda have for many years been exposed to ships and marine craft which abound along our shores. However, with increasing numbers of high-speed, high-powered watercraft, sea turtles have a much more difficult task to elude these vessels. A number of sea turtles are killed in collisions with boats and many more are injured or maimed for life.
By catch in commercial longlines
Loggerheads and leatherbacks are vulnerable to mortality from longline fishing gear. They swallow the baited hooks or become accidentally snagged by the dangling hooks. Loggerheads have been found stranded in Bermuda with the heavy long-line hooks and line still attached.
Entanglement in Commercial Fishing Gear
Although there are no shrimp trawlers in Bermuda’s territorial waters, lost or discarded fishing nets and ropes are often washed up on our shores. On occasion, sea turtles are washed ashore tangled in the rope and twine that served as their death trap. Unable to free themselves from such debris, their struggle to reach the ocean surface for a breath of air fails, due to the weight of their burden, and this results in drowning. In other cases, the turtle becomes so entangled that it is unable to feed and it slowly starves to death.
The practice of trap fishing in Bermuda and elsewhere has been identified as a threat to the ocean-going leatherback turtle which occasionally comes near shore. Through adaptations for speed and power in the open ocean, the leatherback has lost the ability to swim backward which would allow it to extract itself from entrapment.
The leatherback is apparently attracted to the buoys that mark fishing traps and regularly become entangled in the attached line. With forward speed and power the only means of escape, the turtle will swim in circles that can result in a fatal entanglement.
Entanglement in Recreational Fishing Gear
An increasing problem in Bermuda’s territorial waters is entanglement of marine turtles in monofilament. This line often appears to have been discarded by recreational fishermen. Each year several turtles are brought to the aquarium that have drowned or been badly injured by discarded line. This is a problem that the average Bermudian can help with. If you fish and your line becomes entangled on the bottom, do everything you can to retreive the hook and line. If you can’t free the hook, try to get the line to break at the hook or leader by pulling as hard as you can. Don’t cut the line at the reel and then let a long piece of line go underwater.
A serious threat to sea turtles is pollution and debris in our oceans. Those forces that concentrate Sargassum and the post-hatchling turtles that live in weedlines also concentrate marine debris and oil. Epipelagic-size turtles that strand in Bermuda often have small pieces of plastic in their digestive tracts that they undoubtedly mistook for food. Also, species that feed on jellyfish often mistake plastic bags for food. Ingestion of such trash can lead to clogging of the digestive tract and death.
Young turtles in their pelagic phase are dependent on ocean driftlines for food. It is at these driftlines that ocean debris accumulates. Young turtles feeding there are known to ingest plastics, styrofoam, balloons and tar. Tar is the result of weathering of oil at ocean surfaces. The same tar balls that mar the coastline of Bermuda are a threat to pelagic sea turtles.
To find out more about the threats that sea turtles face visit Sea Turtle Conservancy.