Do Fish Use Cold Current To Cross Tropics?

By John Roach
for National Geographic News
February 5, 2003

A big, old Patagonian toothfish found thousands of miles from home is bolstering the theory that large fish can take advantage of very deep, cold ocean waters to cross the tropics from one polar region to the other, swimming under warm water in which they ordinarily could not survive.

The Patagonian toothfish (Dissostichtus eleginoides) is normally found in the icy sub-Antarctic waters off South America. So when a commercial halibut fisherman pulled one in November 2000 from the Davis Straight off the coast of Greenland, he was surprised.

"He knew he had never seen this one before and was unable to find it in any of his local fish fauna guide books," said Peter Rask Møller, a zoologist at the University of Copenhagen in Denmark.

The fisherman, Olaf Sólsker, froze the odd fish and brought it ashore. None of the local fisheries biologists were able to identify the specimen. Eventually, the fish made its way to Møller and colleagues who identified it as a Patagonian toothfish. They report the discovery in the February 6 issue of the journal Nature.

Prior to this discovery, the species, commonly known as Chilean sea bass and served as a delicacy at restaurants in the U.S., Europe, and Asia, had not been recorded north of Uruguay in the Atlantic and north of Chile in the Pacific.

"To find a Chilean sea bass in northern Arctic is certainly a novel find," said Thomas Hilbish, a professor of biological sciences at the State University of New York at Stony Brook. "It does strongly suggest there is some sort of route for trans-equatorial migration."

But how did it get there?

Transequatorial Migration

Many marine species have what scientists refer to as anti-tropical distribution patterns, meaning that the same species has separated populations on either side of the equator. Great white sharks and humpback whales are some of the most well-known examples of this.

"The present catch of a strictly southern hemisphere deep-water fish supports an old and widely accepted theory that today's anti-tropical distribution pattern is a result of earlier migration through the warm tropics," said Møller.

Continued on Next Page >>


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