Reptiles
Loggerhead Sea Turtle
Caretta caretta · also called loggerhead, loggerhead turtle
The loggerhead is the most numerous sea turtle in the world, and the one most likely to be seen off temperate coasts. It is a heavy, russet-shelled, big-jawed animal that spends its life crossing whole oceans, guided by a magnetic sense that lets it find a single beach after thirty years away.
Overview
Loggerheads range through the temperate and subtropical zones of every ocean and the Mediterranean — much cooler water than most sea turtles tolerate. As adults they feed in relatively shallow coastal waters over reefs, rocky bottoms, and continental shelves, and they also cross open ocean between feeding and breeding areas. Major nesting concentrations are on the beaches of the southeastern United States, Cape Verde, Oman, Western Australia, and Greece.
The shell-crusher
The loggerhead is named for its disproportionately large head, which packs the jaw muscles and broad crushing plates it uses on hard-shelled prey — crabs, whelks, conchs, clams, sea urchins, and the occasional jellyfish or sponge. Its heavy, slightly heart-shaped carapace is reddish-brown, often carrying a garden of barnacles, algae, and small crabs.
Navigating by magnetism
Loggerheads are a leading model for magnetic navigation in animals. They detect both the inclination and the intensity of the Earth’s magnetic field, and since both quantities vary geographically, a turtle effectively has access to magnetic “coordinates.” Hatchlings inherit a map that steers them onto the right ocean currents; adults use the same sense for natal homing, returning to nest within a few tens of kilometres of where they themselves hatched.
Life cycle
Females come ashore at night every two to four years, haul up the beach, dig a nest chamber, and lay around 110 eggs, repeating this several times a season. Sand temperature sets the hatchlings’ sex — warmer sand gives females — and on many beaches, warming has pushed the ratio to over 90% female. Hatchlings dash to the sea and vanish into the open ocean for their “lost years,” returning to coastal habitat only once they are large juveniles. Maturity takes about 30 years.
Threats and conservation
The loggerhead is Vulnerable. The single largest killer is fisheries bycatch — hooked on longlines, caught in trawls and gillnets — followed by coastal development and artificial light (which disorient nesting females and hatchlings), egg poaching, boat strikes, and plastic pollution. Feminisation of hatchling cohorts from hot beaches is an emerging climate threat. Sustained conservation works: turtle excluder devices on trawl nets, hook and gear reforms, beach protection, and lighting ordinances have driven strong recoveries of the US and Cape Verde populations.
Loggerhead Sea Turtle: common questions
How does a loggerhead turtle navigate across an ocean?
With a magnetic map. Experiments show loggerheads sense both the angle (inclination) and the strength of the Earth's magnetic field, and because these vary predictably across the globe, a turtle can work out roughly where it is and which way to swim. Hatchlings are born with an inherited "magnetic map" of the current system they need to ride, and adults use the same sense to find their way back to the specific stretch of coast where they hatched, decades and thousands of kilometres later. This "natal homing" means each beach's turtles are a somewhat distinct population.
Why does the loggerhead have such a big head?
To crush shells. The loggerhead specialises in hard-bodied prey — crabs, conchs, whelks, clams, sea urchins — and its large head houses the massive jaw muscles and broad, blunt crushing surfaces needed to break them open. Green turtles (plant-eaters) and hawksbills (sponge specialists) have narrower heads suited to their diets.
What are the "lost years"?
The period, roughly the first decade of life, when young loggerheads leave the nesting beach, swim out to sea, and effectively disappear from human observation. They spend these years drifting and feeding in the open ocean — Atlantic hatchlings ride the currents of the North Atlantic gyre and shelter in mats of Sargassum seaweed — before eventually returning to shallow coastal waters as larger juveniles. Satellite tags small enough for young turtles are only now filling in this gap.
Is the loggerhead endangered, and what threatens it?
It is listed as Vulnerable globally, with the picture varying by region — the southeastern US and Cape Verde populations have grown strongly under protection, while some others are still declining. The main threats are bycatch in longline, trawl, and gillnet fisheries (the biggest single cause of death), coastal development and lighting that disrupt nesting, egg poaching, boat strikes, plastic ingestion (turtles mistake bags for jellyfish), and rising sand temperatures that are skewing hatchlings heavily toward female.