Loggerhead Turtle

A young loggerhead starts out as a dark hatchling only about 4.6cm long, which races to the sea and swims far offshore to shelter in floating Sargassum weed until it has grown to about 45cm.

Hatchlings live among the floating mats in the open ocean, then move to coastal waters and shallow estuaries as they grow. Older juveniles keep to the continental shelf and to shallow estuaries, and in the northwestern Atlantic they use estuaries with limited access to the ocean more than non-nesting adults do. The Mediterranean works as a nursery, with almost half of its juveniles arriving from the Atlantic, and upwelling off Baja California feeds large numbers of young turtles and subadults.

Appearance

At hatching a turtle weighs about 20g and is light brown to almost black, with none of the yellows and reds of an adult. Males and females look the same until adulthood.

Behaviour

Once afloat a hatchling lets the undertow carry it the first few metres from shore, then swims for around 20 hours. A very young turtle also swims differently from an adult, holding its front flippers against the shell and kicking with the hind ones, and it moves over to the adult's alternating stroke by the age of one. Young loggerheads handle cold better than adults, not becoming stunned until the water falls below 9°C. On seasonal migrations juveniles steer by magnetic and visual cues together, and can manage with either one alone.

Feeding

The Sargassum works as cover and as a larder. It can hold as many as 100 animal species, and young turtles take barnacles, crab larvae, fish eggs and hydrozoans, along with ants, flies, aphids and beetles blown in on the wind. Adults, by contrast, feed mostly on invertebrates from the bottom.

Life cycle

Eggs are buried on the beach above the high-tide line and take about 80 days to incubate, and the warmth of the nest decides the sex, with about 30°C giving an equal mix. The central eggs of a clutch usually give the biggest, fastest-growing and most active hatchlings. The young dig their way out, usually at night, when darkness gives more cover and the surface sand is less hot, and head for the brighter horizon made by moon and starlight on the water. Many stay with the Sargassum, then move to nearshore water as juveniles. Maturity is still many years off, at 17 to 33 years.

Threats

Young turtles have far more enemies than adults. Ghost crabs, ants, beetles, snakes, gulls, foxes, raccoons, feral dogs and feral pigs all raid nests. Crabs, lizards, snakes and seabirds pick off hatchlings on the way down the beach, and crabs and fish such as parrotfishes and moray eels take them at sea. Introduced foxes once destroyed up to 95 percent of the clutches on one stretch of eastern Australia, and raccoons have taken nearly every clutch on some Florida beaches, though removing foxes and covering nests with wire mesh have helped.

Bright lights on developed coasts lure hatchlings inland, where they dry out or are eaten, and this kills tens of thousands a year. Cyclones flood nests and drown the embryos, and unusually warm sand can produce almost all females. At sea, juveniles gather in feeding areas that overlap with fishing, and many are caught by accident.