A new hope to ease fisheries crisis

It's long been the most important and contentious question in the fisheries crisis facing New England and the world: How many fish are left in the sea?

Yesterday, a group of Boston-area researchers announced they have found a way to help answer that question with a sonar technique that ''illuminates" schools of fish over an area a million times larger than what could previously be studied. Until now, scientists have only been able to track fish in limited bands in the murky depths, providing incomplete snapshots that have been sharply criticized by fishermen because they have served as the foundation of tight government limits on their catches.

''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, a Massachusetts Institute of Technology associate professor of mechanical and ocean engineering and lead author of the report published in the journal Science.

Makris and his team were able to continuously track enormous schools of fish, some of them tens of miles long, under an ocean surface area as large as 6,000 square miles, about the size of Connecticut. The technique cannot detect individual fish, and no sonar can identify species of fish, but it could help scientists more accurately estimate the quantity of fish overall in a region of the ocean and how they behave.

The new technique will be tried out this year on Georges Bank, an important fishing ground more than 60 miles off Massachusetts.

Even if the test succeeds, the region's fishermen may be leery of the new technique, because they have grown distrustful of scientists and their methods, after years of contesting what the fishermen believe are imperfect fish counts. Those counts showed that stocks of dozens of fish species such as cod and flounder plunged in the past and are still not rebuilding fast enough, leading the government to put stiff limits on fishermen's catch and on the number of days they can go to sea. Many have gone out of business.

Fishery managers were debating additional restrictions on fishing yesterday because scientists say too many fish are being taken. The proposed rules could reduce the number of days most fishing vessels can go to sea annually by about five, to about 47 days.

Fishermen said yesterday that more accurate ways to count fish are needed, but they fear they will be forced out of business before that can happen.

''This sounds interesting; we need to explore new technologies to count fish," said David Bergeron, executive director of the Massachusetts Fishermen's Partnership, an umbrella organization of fishing groups. He had not seen the study.

''Unfortunately, things keep marching forward in the regulatory realm," Bergeron said.

Counting fish is a complex problem: Fish don't stay in one place, and they aren't easy to see in the ocean. New England scientists use a suite of methods to count fish, including casting out nets in hundreds of randomly selected locations, as well as sending out a continuous, concentrated sound wave below a ship. The echo it sends back can tell scientists how many fish are in that water column and where they are in it. This information, along with data on fishermen's catch, is fed into a computer, and a model calculates fish populations. Fish managers then use the information to set restrictions on fishermen.

Makris also uses sound waves, but at a much lower frequency that can travel far greater distances through water. A device dangled from a ship emits pulses of sound underwater. Another ship receives the echo of the sound as it bounces off schools of fish.

Purnima Ratilal of Northeastern University and other researchers from MIT and the Naval Research Laboratory worked on the study, which was funded by the Office of Naval Research, the Alfred P. Sloan Foundation, and the National Oceanographic Partnership Program.

Still, there are drawbacks: At least for now, the technique is probably best used for fish such as herring, mackerel, and scup that tend to travel in large concentrated schools midway between the surface and ocean floor, where it is easier to detect them. Makris's method would not help scientists better count flounder, for example, because it can be hard to distinguish them from the ocean floor, where they spend much of their time.

Fishery scientists say the acoustic method will probably add to, not replace, traditional fish counting. For example, Makris's big-picture data could help scientists understand the behavior of fish and overall numbers, while research vessels will figure out what species they are seeing.

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

Makris was not looking for fish when he started; he wanted to see if the device could locate ancient riverbeds under the ocean floor. But soon, he realized he was seeing fish, millions of them in enormous groups that no one had seen before. He and his team ran an experiment to track the schools off Long Island, N.Y.

Both large and small schools would congregate in an hourglass pattern early in the morning, with a thin bridge of fish connecting the two groups. By afternoon, the hourglass would break up. By the next morning, researchers saw the consolidated hourglass design again, but it is unclear whether it was the same group of fish.

The fish also appear to be communicating in this pattern, because researchers detected faint ripples moving through the schools, like the ''wave" that moves through the fans at Fenway Park. The ripples were moving far faster than fish could swim. Far more research is needed to understand why fish behave like this, but fisheries officials say it may help in predicting fish movements and managing them.

''It's very exciting," said Michael Jech, research fisheries biologist with the National Marine Fisheries Service in Woods Hole. ''We see fish in an aquarium and try to extrapolate what they are doing in the ocean. Now, we can really see them."