Can Crocodiles Live in Salt Water? How Salt Glands Work

Why salt water is a problem for reptiles

Sea water is about three times saltier than the body fluids of a crocodile. An animal living in it constantly gains salt, through its food and any water it swallows, and loses water through its skin and breath. Too much salt in the blood damages cells, so marine animals need a way to get rid of it.

Mammals in the sea, such as dolphins, rely on powerful kidneys. Reptile kidneys cannot make urine saltier than the blood, so marine reptiles evolved salt glands instead. Sea turtles have them near the eyes, sea snakes under the tongue and marine iguanas in the nose. Crocodiles have them on the tongue.

How crocodile salt glands work

In 1981 the Australian zoologists Laurence Taplin and Gordon Grigg reported that the saltwater crocodile has dozens of small salt-secreting glands embedded in the surface of its tongue. Each gland opens through a tiny pore, and when the crocodile has too much salt in its body, the glands release a concentrated salty fluid that is lost into the water.

The glands work best when the crocodile is loaded with salt, for example after feeding on marine fish or crabs. Together with skin that lets little water through and a habit of not drinking sea water, they allow saltwater crocodiles to live in hypersaline mangroves and coastal waters for weeks or months.

Similar lingual salt glands have been found in other members of the crocodile family, including the American crocodile, the Nile crocodile and the Australian freshwater crocodile. They work better in some species than in others, which helps explain why only a few crocodiles regularly live in the sea.

Why alligators cannot live in salt water

Alligators and caimans have similar glands on the tongue, but they secrete very little salt. As a result, the American alligator lives mainly in freshwater swamps, rivers and lakes. It can enter brackish marshes and has even been seen swimming in the sea off Florida and the Gulf Coast, but it has to return to fresh water within days.

Scientists think the ancestors of all crocodilians may have been more tolerant of salt water, and that alligators lost this ability after their lineage settled in freshwater habitats. Being able to cope with salt water is one reason true crocodiles have spread across the tropics while alligators survive in only two countries, the United States and China. For other differences, see alligator vs crocodile.

Crocodiles that live in salt water

The American crocodile is a good example from the Western Hemisphere. In southern Florida it lives mostly in brackish and salt water around Florida Bay, the Keys and mangrove coasts, which is why Florida is the only place in the world where wild crocodiles and alligators live side by side. Its hatchlings need access to lower-salinity water, and rain-fed pools near nesting beaches are important for them. Read more in are there crocodiles in Florida?

Ocean journeys of saltwater crocodiles

Saltwater crocodiles are not fast long-distance swimmers. Instead they use the sea in a clever way. In a study published in 2010, researchers fitted 20 crocodiles in the Kennedy River in Queensland with tracking tags. Several of them left the river and traveled along the coast. One crocodile covered about 590 km (370 mi) in 25 days, swimming from the east coast around Cape York to the Gulf of Carpentaria, and another about 411 km (255 mi) in 20 days.

The tracking showed that the crocodiles rode surface currents. When the current flowed in their direction they moved quickly with little effort, and when it turned against them they rested in sheltered bays until it changed. Some crocodiles found at sea carry barnacles on their scales, a sign of long periods in salt water.

Island hopping across the Pacific and Indian Oceans

Current-riding helps explain the huge range of the saltwater crocodile, which reaches from eastern India to Palau, the Solomon Islands and Vanuatu. Wandering individuals have turned up far outside the normal range, including historical records from Japanese waters. Crocodiles once lived in the Seychelles, more than 3,000 km (1,900 mi) from the nearest population today, before they were wiped out about two centuries ago.

These ocean crossings are not migrations. They are usually made by young crocodiles, often males, pushed out of crowded rivers by larger, dominant animals. Most stay close to coasts, and none live permanently in the open ocean, because crocodiles still need land for basking and nesting and fresh water for raising their young.