Researchers shed more light on acrobatic salmon sharks

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October 30, 2005

Researchers shed more light on acrobatic salmon sharks
By ANNE PINCKARD
SENTINEL CORRESPONDENT

Salmon sharks, the enigmatic predators of the deep, may soon lose some of their mystery, thanks to scientists who, using a new satellite tracking system, have been tracking the sharks' movements for more than three years.

Their findings, published recently in the journal Science, tracked 48 salmon sharks over thousands of miles, through extreme temperature changes, and to depths up to 450 feet.

Salmon sharks are the closest living relatives of great whites.

Averaging 400 pounds and 8 feet in length, the sharks annually congregate in the waters of Prince William Sound, Ala., to feed on salmon. The sharks are known for their acrobatic feeding behavior.

"They literally jump out of the water," said Randy Kochevar, marine biologist at Monterey Bay Aquarium.

The researchers, from Stanford University Hopkins Marine Station, National Marine Fisheries Service, Monterey Bay Aquarium and the Alaska Department of Fish and Game, used two sophisticated tags to track the sharks' location and get data from the environments where the sharks swim. By downloading this information onto a computer, the researchers received updates on the shark's location on a daily basis.

"It's the first study of this magnitude using near real-time tracking," Kochevar said.

Research in this area has become critical as the world population of sharks has been declining. Scientists do not fully understand the reasons, though overfishing is a likely cause. Sharks are also caught and killed in fishing nets.

The researchers trapped the sharks using baited hooks. Once lured, the shark is surrounded by a float and then brought along side the boat. The sharks are secured, and the researchers attach the tags to the dorsal fins.

The Smart Position-Only Tag sent information to the satellite each time the shark surfaced. As the sharks often swim with their fins out of the water in a way made famous by the movie "Jaws," the satellites provided timely information about the shark's location.

The Pop-Up Satellite Archival Tag remained attached to the shark until released at a specified time. Upon surfacing, it would send information about the depth, temperature and light levels from the deep ocean to the satellite.

This technology "will rapidly become important for pushing the frontier of shark biology," said Kevin Weng, researcher at Stanford Hopkins Marine Laboratory.

"We're exploring the potential of using these tags to do even more things than they are doing right now," said Kochevar. Since sharks go where we cannot, they can obtain data from previously unknown areas of the deep. Oceanographers can use the information to create a profile of the ocean.

The satellite tracked the sharks as they moved from the coast of Alaska all the way to the Hawaiian islands.

Such seasonal, long-distance migrations are unusual in sharks, said Weng. One shark swam over 11,300 miles, a distance equivalent to half the earth's circumference, in less than two years.

The sharks were very active off the coast of California. They may travel to feed or to pup, said Weng. Salmon sharks have been spotted in the Santa Cruz area, according to Kochevar. However, they are often mistaken for great white sharks.

The study also gave insight into "the endothermic fish paradox," a mystery that has been troubling scientists for years. Salmon sharks, along with great whites, are one of the few fish that are endothermic, or have the ability to keep their tissues warm. Warm muscles allow the sharks to swim at high speeds, up to 57 miles per hour. Their hearts, however, remain cold because the blood circulates from the gills, where it is exposed to the frigid water. Cold muscles become sluggish, and at the low temperatures the sharks experience, our hearts would stop. So how does the shark heart muscle keep pumping?

"What we found was that the salmon sharks have some key proteins in the heart muscle tissue," said Weng. Such proteins are commonly found in high concentration in mammals and birds, but is typically not found in fish. These proteins are important in controlling the heart beat.

The salmon shark project is part of the "Tagging of the Pacific Pelagics" project. So far, 22 species of marine mammals are tracked.

"Many sharks are threatened by fishing around the world," the authors of the study wrote.

Contact Anne Pinckard at tdunlap@santacruzsentinel.com.