Sea turtles are ancient reptiles whose journey from egg to adult is fraught with danger, with different predators targeting them at every life stage. The vulnerability of a sea turtle changes drastically depending on its size and age. A soft-shelled egg buried in the sand and a massive, armored adult in the open ocean face entirely separate sets of threats.
Threats to Nests and Eggs
The nesting stage represents the first significant hurdle in a sea turtle’s life, as eggs are a high-calorie, stationary target for terrestrial predators. Mammals are the primary threat, often using their keen sense of smell to locate the clutch buried beneath the sand. Common nest raiders include raccoons, foxes, coyotes, and feral dogs or pigs, which systematically dig up the nests to consume the eggs.
In some regions, the threat extends to other animals like monitor lizards and dingoes, which target flatback turtle nests in Australia. Ghost crabs are also significant predators on the beach, sometimes digging down to reach the uppermost eggs. Ants, particularly fire ants, can swarm a nest, feeding on both the eggs and weak hatchlings before they emerge.
Predators excavate the nest chamber and consume the contents, often resulting in the destruction of the entire clutch. This high rate of loss at the egg stage is a natural check on population numbers. However, human development near nesting beaches can inadvertently increase the density of these predators, leading to unnaturally high rates of nest loss.
Predators of Hatchlings
The period between leaving the nest and reaching the open ocean represents the stage of highest mortality for sea turtles. Once hatchlings emerge, they must cross the beach, where they are immediately vulnerable to terrestrial and aerial predators. Ghost crabs wait in the dunes and along the water’s edge, ambushing the tiny turtles as they scurry toward the sea.
Birds patrol the shore, swooping down to snatch the hatchlings from the sand.
- Gulls
- Frigatebirds
- Herons
- Crows
The mortality rate during this dash is extremely high, with estimates suggesting that more than 90% of hatchlings are consumed by predators. Once they enter the water, the threat shifts to aquatic species.
In the shallow coastal waters, hatchlings face predatory fish such as snapper, barracuda, and grouper. They must swim quickly to avoid being eaten before they can reach the open ocean currents. Even in deeper waters, the young turtles are still susceptible to larger bony fish and smaller sharks.
Specialized Predators of Mature Sea Turtles
Once sea turtles reach a larger juvenile or mature size, their hard shells and sheer bulk provide a strong defense against most predators, greatly reducing their list of natural threats. The few animals capable of successfully preying on adults are highly specialized or exceptionally large marine carnivores. The Tiger Shark is the most well-known and frequent predator of large sea turtles worldwide.
Tiger sharks possess broad heads and uniquely curved, heavily serrated teeth, which are adapted to cut through the turtle’s thick carapace. These sharks often employ an ambush strategy, attacking the surfacing turtle from below to inflict a devastating bite. The turtle’s defense involves keeping its shell presented to the shark and maneuvering tightly to prevent a fatal bite to its softer flippers or head.
Other large sharks, such as Great White Sharks and Bull Sharks, have been recorded preying on sea turtles, but they do not specialize in them to the same degree as the Tiger Shark. Other apex predators also pose a significant threat. Saltwater crocodiles in the Indo-Pacific and American crocodiles prey on adult turtles both in the water and on nesting beaches. Killer whales have also been observed to occasionally prey on leatherback sea turtles.