Tagged Tuna Reveal Migration Secrets

Helen Scales
for National Geographic News
August 13, 2007

High-tech electronic tags are unveiling new insights into the migration and spawning secrets of Atlantic bluefin tuna, according to a pair of new studies.

The work could lead to better protections for the commercial species, which many experts say is declining worldwide (see related photos of the demand on tuna fisheries).

In one report, appearing in the journal Hydrobiologia, a team of international scientists documented two giant bluefins tagged within minutes of each other off the coast of Ireland.

The two fish swam to opposite sides of the Atlantic Ocean—ending up more than 3,000 miles (5,000 kilometers) apart.

One of the fish traveled 3,730 miles (6,000 kilometers) southwest to waters about 186 miles (300 kilometers) northeast of Cuba. The other remained in the eastern Atlantic and moved off the coasts of Portugal.

The fishes' dramatic separation supports theories that two distinct tuna stocks forage in common grounds but swim thousands of miles apart to breed in the Gulf of Mexico and the Mediterranean (see graphic).

For another unrelated study, a U.S. team used the high-tech tags on 28 tuna to identify the particular habitats of the bluefins that spawn in the Gulf of Mexico.

The work—to appear in an upcoming issue of the journal Marine Biology—found that the fish seem to prefer breeding grounds where the continental shelf is steep and the temperature is between 75 and 81 degrees Fahrenheit (24 and 27 degrees Celsius).

This suggests that even small changes in ocean temperatures could affect when and where bluefins breed.

Rise and Fall

The Atlantic bluefin tuna is listed as "data deficient" on the World Conservation Union's Red List of Threatened Species.

This means that researchers simply don't have enough data on the species' population and distribution to assess its risk of extinction.

Continued on Next Page >>


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