Leatherback sea turtles, Dermochelys coriacea, are unique among sea turtles due to their lack of a bony shell, instead having a tough, rubbery carapace. These turtles are the largest living turtles, reaching lengths of up to 2.7 meters (8 ft 10 in) and weights of 500 kilograms (1,100 lb). They are also known for their extensive migrations, traveling thousands of miles, and their ability to dive to nearly 4,000 feet, deeper than most marine mammals. Despite their wide global distribution, found in every ocean except the Arctic and Antarctic, leatherback populations are rapidly declining, leading to their classification as endangered.
Threats from Fishing Activities
Fishing practices threaten leatherback sea turtles, primarily through incidental capture, or bycatch. Commercial fisheries, particularly those using longlines, gillnets, and trawls, often interact with them. Leatherbacks can become entangled in gillnets or trawl nets, preventing them from surfacing to breathe and often leading to drowning.
Longline fisheries, which deploy thousands of baited hooks on a single line stretching for miles, also pose a risk. Turtles can become hooked externally or ingest hooks, causing severe injury or death. For example, a 2004 estimate suggested that global longlining fleets captured between 50,000 to 60,000 leatherbacks in a single year.
Ghost fishing gear, abandoned, lost, or discarded nets and lines, continues to entangle and drown marine life, including leatherbacks, long after being abandoned. Efforts to mitigate bycatch include using specific hook types, such as circle hooks, and different bait types; for instance, using fish bait instead of squid bait, can reduce capture probability. Despite mitigation efforts, the global scale of fishing operations means bycatch remains a primary cause of leatherback mortality.
Impacts on Nesting and Foraging Habitats
Human activities are degrading and destroying the habitats leatherback turtles rely on for nesting and foraging. Coastal development, such as homes and resorts, reduces available beach space for nesting and alters shoreline vegetation, contributing to erosion. This loss of nesting sites threatens population survival.
Artificial beachfront lighting from these developments disorients both nesting females and emerging hatchlings. Adult females may crawl away from the ocean, becoming exhausted, while hatchlings, naturally drawn to the ocean horizon, may move inland, increasing their vulnerability to predators. In some regions, direct harvesting of leatherback eggs or adults also impacts population recovery, contributing to declines.
Foraging habitats, such as areas rich in jellyfish, their primary food source, are affected by human activities. While specific degradation mechanisms vary, changes to these marine environments can reduce prey availability or expose turtles to additional dangers. Understanding and protecting both nesting and foraging grounds are important for conservation efforts.
Climate Change Effects
Global climate change threatens leatherback turtles. Rising sea levels impact nesting beaches by inundating them, reducing available area for egg-laying. This erosion, exacerbated by increased storm frequency and intensity, can lead to lower nesting success.
Increased temperatures on nesting beaches influence temperature-dependent sex determination (TSD) in sea turtles. Hatchling sex is determined by sand temperature during incubation: lower temperatures produce males, higher temperatures produce females. As global temperatures rise, nesting beaches can become predominantly female-producing, leading to skewed sex ratios with fewer males, which can impair population viability and genetic diversity.
Changes in ocean currents and prey distribution, driven by warming waters, can also affect leatherback foraging success. These shifts may force turtles to travel further or encounter less abundant food sources, impacting their health and reproductive capabilities. The combined effects of habitat loss, altered sex ratios, and disrupted foraging patterns highlight climate change’s influence on leatherback survival.
Pollution and Other Human-Caused Dangers
Pollution, particularly plastic debris, threatens leatherback turtles. These turtles primarily feed on jellyfish, frequently mistaking plastic bags and other floating debris for their natural prey. Ingesting plastic can lead to intestinal blockages, internal injuries, and a false sense of fullness, resulting in malnutrition and starvation. A significant percentage of leatherback turtles have ingested plastic.
Vessel strikes, collisions with vessels, are another danger. Leatherbacks are susceptible because they often rest or forage near the surface, making them vulnerable to fast-moving watercraft. Injuries from vessel strikes can range from severe lacerations and blunt force trauma, which can be immediately fatal, or internal damage leading to a slow decline.
Underwater noise pollution, generated by activities such as shipping, oil and gas exploration, and construction, overlaps with leatherback habitats. While sea turtles do not vocalize for communication, they use sound for environmental awareness, navigation, locating prey, and avoiding predators. Research indicates that turtles can experience temporary hearing loss from exposure to intense underwater noise, which can impair their ability to detect sounds and navigate their environment.