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Scientists Tracking Fish With Wide-Area Sonar

A group of Boston-area scientists has come up with what they say is a better way of tracking and estimating fish populations, which in turn could change the way fishery regulators manage the resource.

The new sonar technique is able to scan for fish over an area a million times larger than what could previously be studied, the report's lead author said.

"I've had these dreams where you are floating in the water in the darkness and look down and suddenly see everything; that's what this is like," said Nicholas Makris, an associate professor of mechanical and ocean engineering at the Massachusetts Institute of Technology and lead author of the report in the journal Science.

The current methods for estimating fish populations — used by regulators to limit days at sea and catch sizes in an effort to rebuild populations of some species — have been sharply criticized by the fishing industry as inaccurate.

The new method can track large schools of fish under an ocean surface as large as 6,000 square miles — roughly the area of Connecticut.

The drawback is that the technique cannot identify species of fish and does not work well tracking bottom dwelling fish because it can be hard to distinguish them from the ocean floor.

The new method is scheduled to be tried out this year on Georges Bank, the fertile fishing ground about 60 miles off the coast of Massachusetts.

Fishermen are often distrustful of scientific methods of counting fish. What regulators count often does not jibe with what fishermen are experiencing on the ocean.

Still, any new technology that may help would be welcome.

"This sounds interesting. We need to explore new technologies to count fish," said David Bergeron, executive director of the Massachusetts Fishermen's Partnership. He had not seen the study.

Current methods of counting fish include casting nets in hundreds of randomly selected locations; sending out sound waves directly below a ship's hull that can only count fish in a narrow column; and studying catches. All the information is fed into a computer to calculate fish populations.

At a meeting earlier this week in Portland, Maine, the New England Fishery Management Council approved new regulations calling for a reduction in days at sea and other measures to help rebuild cod and flounder populations in New England waters.

The new method uses low frequency sound waves that travel greater distances, Makris said. A second ship receives the echoes that bounce off schools of fish.

The method could be used in conjunction with current fish counting methods, a federal regulator said.

"It gives us a different perspective," said Steve Murawski, chief scientist for the National Marine Fisheries Service, who had seen the study. "Our mission covers 4 million square miles and 900 species, and anything that gives us new information is helpful."

The original goal of the study was not to track fish, but to locate ancient riverbeds under then ocean floor, Makris said. But he soon realized that he was seeing enormous schools of fish, perhaps millions strong.