How Turtles Navigate Ocean Currents

The East Australian Current (EAC) is a well-known water current that plays a crucial role in transporting turtles between habitats across the southern Pacific Ocean. This current system helps convey animals from one place to another, and in the case of turtles, it offers a free ride to their destination. The EAC is not just a convenient mode of transportation for turtles, but it also has a significant impact on the climate and ecosystems of the east coast of Australia. It flows southward from the Great Barrier Reef with speeds of up to 7km per hour and transports an impressive volume of water. The EAC is just one example of how water currents influence the migration patterns of turtles and other marine species, contributing to the stitching together of all the world's oceans.

How do turtles navigate?

It's thought that turtles may use a number of clues to find their way, including ocean currents, the Earth's magnetic field, and water chemistry. For example, in the Atlantic, baby sea turtles ride ocean currents away from their birth beaches into the Sargasso Sea, and then back again when they're old enough to reproduce. The East Australian Current (EAC) is also a well-known route for turtles, transporting them from Australia to South America.

The puzzle of the loggerhead life cycle in the southern Pacific Ocean was solved by tracing the path of the currents. A genetics study showed that little loggerheads from Australia and New Caledonia, small juveniles in New Zealand, and larger juveniles in Peru are all connected by major currents that link opposite sides of the southern Pacific Ocean.

It's not just turtles that use these ocean currents to get around. Salmon in the North Pacific, for example, ride massive current-driven gyres until they are old enough to return to spawn and die in the streams where they were born.

Why do turtles ride water currents?

Sea turtles have been observed riding water currents, such as the East Australian Current (EAC), to travel between habitats. This behaviour is not limited to the EAC, as turtles also ride other ocean currents like the Humboldt Current and the South Equatorial Current (SEC).

The EAC, in particular, plays a crucial role in transporting turtles across the southern Pacific Ocean. It flows southward from the Great Barrier Reef along the east coast of Australia, with speeds in its core reaching up to 7 km per hour. This current is part of a larger system of currents known as the "global ocean conveyor" or thermohaline circulation (THC), which stitches together all the oceans of the world.

By riding these currents, turtles can cover vast distances with minimal effort. For example, Australian-born loggerhead turtles have been found to undertake a 20,000-kilometre round trip across the Pacific Ocean by utilising the EAC and other currents. This behaviour is not limited to sea turtles, as other species such as American eels and salmon also take advantage of ocean currents for migration.

While the exact mechanisms are not fully understood, adult turtles are believed to use a combination of clues, including ocean currents, the Earth's magnetic field, and water chemistry, to navigate back to their natal beaches for breeding. This homing behaviour is also observed in other species, such as salmon, which return to their streams of origin to spawn.

Additionally, sea turtles are known to migrate between foraging and nesting grounds, as well as to warmer waters seasonally. These migrations can span hundreds or even thousands of miles. By riding ocean currents, turtles can conserve energy and efficiently travel the long distances required for their life cycles.

Where do turtles ride water currents to and from?

Sea turtles ride ocean currents to and from various destinations, sometimes travelling hundreds or even thousands of miles. They migrate between foraging and nesting grounds, as well as to warmer waters during the colder seasons.

In the Pacific Ocean, sea turtles born in Japan migrate almost 8,000 miles to the waters off Baja California, Mexico, to feed and mature. Once sexually mature, they migrate back to Japan to breed and nest.

In the Atlantic Ocean, leatherback sea turtles migrate from Caribbean beaches up the US East Coast to Canada. In the Pacific, they migrate from Southeast Asia (Indonesia and Malaysia) to California and then up to Alaska.

A notable example of sea turtles riding water currents is the East Australian Current (EAC), popularised in the animated film "Finding Nemo." In reality, the EAC is not a narrow, fast-flowing current as depicted in the movie, but rather a much wider and wilder current, transporting an immense volume of water southward along the east coast of Australia.

Hatchling loggerhead turtles from Australia and New Caledonia ride the EAC southward, eventually reaching Peru and northern Chile on the eastern side of the Pacific Ocean. This journey across the southern Pacific Ocean is facilitated by the southward-flowing current of the South Pacific Gyre, which slingshots the tiny turtles eastward as the EAC moves away from the Australian coast.

The use of ocean currents by sea turtles highlights the importance of international collaboration in studying and protecting these migratory species.

How far do turtles migrate?

Sea turtles are known to migrate long distances, often travelling hundreds or even thousands of miles. Some sources state that sea turtles can migrate up to and over 10,000 miles per year.

Leatherback sea turtles are among the most highly migratory sea turtles, travelling up to 10,000 miles or more each year between foraging grounds in search of jellyfish. In the Atlantic, they migrate from the Caribbean up the US East Coast to Canada. In the Pacific, they migrate from Southeast Asia (Indonesia and Malaysia) to California and then up to Alaska.

Loggerhead turtles born in Japan migrate almost 8,000 miles to the waters off Baja California, Mexico, to feed and mature. Once they have reached sexual maturity, they migrate back to Japan to breed and nest.

In February 2020, a sea turtle named Yoshi travelled around 22,000 miles round trip from Australia to the eastern coast of Angola, Africa, and back again.

Green sea turtles in Hawaii travel around 1,200 miles round trip each year from the main Hawaiian Islands to reproduce and nest at French Frigate Shoals in the Northwestern Hawaiian Islands.

The ability of adult sea turtles to travel to precise targets has led many to wonder about their navigational mechanisms. It is not known exactly how adult turtles are able to navigate to their natal beaches, but researchers think they may use a number of clues, including ocean currents, the Earth's magnetic field, and water chemistry.

How do scientists track turtles?

Scientists have a few different methods to track turtles, including the use of satellite telemetry, radio telemetry, and fluorescent powder.

Satellite Telemetry

The most common method is satellite telemetry, which involves attaching a Platform Terminal Transmitter (PTT) to the turtle's shell. This transmitter sends a signal to an orbiting satellite each time the turtle surfaces for air. The satellite then retransmits the data to a receiving station on Earth that researchers can access via their computers. The data received includes digital codes that researchers must decipher to determine the turtle's location, number of dives in the last 24 hours, water temperature, and more. This technology has advanced to the point where researchers can track turtles in the open ocean, providing valuable insights into their migratory patterns, behaviour, and marine habitats.

Radio Telemetry

Radio telemetry is another method used to track turtles, particularly in local parks and smaller areas. A radio transmitter is attached to the turtle's carapace (upper shell) using a special type of glue. Researchers can then use a silver three-pronged antenna and attached receiver to detect the signal frequency and locate the turtle by following the "beeping" sound. This method is useful for understanding movements within a turtle's home range and daily requirements, such as food, shelter, and thermoregulation.

Fluorescent Powder

A more labour-intensive but detailed method involves applying non-toxic fluorescent powder to the turtle's plastron (underside). As the turtle moves, it leaves a distinct trail that can be illuminated and traced using an ultraviolet light at night. This technique provides a more accurate picture of the turtle's daily movements and how it utilizes its home range.

Overall, these tracking methods provide valuable insights into the migratory patterns, behaviour, and habitat usage of turtles, which can inform conservation efforts and help protect these fascinating creatures.

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