Biologists hope to track fish with high-tech sensors

Posted: Friday, March 22, 2002

ANCHORAGE (AP) -- Researchers seeking to unravel the mystery of salmon migrations in the northern Pacific want to build a high-tech fish-sensing network stretching thousands of miles from California to Alaska.

Scientists with the Pacific Ocean Salmon Tracking program, known as POST, propose building an array of acoustic sensors along chokepoints in known salmon migrations.

The underwater network of receivers would be mounted on buoys moored along the continental shelf and would track the migration of fish along the coasts of Alaska, British Columbia, Washington, Oregon and California.

Data collected by sampling salmon from nets suggest that migrating juvenile salmon follow the continental shelf.

''If we're right that we can do it,'' says POST co-chairman David Welch, ''we will basically give marine science something that's the equivalent of a Hubble Telescope.''

The array, once in place, could also be used to track other oceangoing animals.

Organizers announced the plan in February in Honolulu at the American Geophysical Union's 2002 Ocean Sciences meeting, the world's largest gathering of ocean scientists. The project is just one facet of the Census of Marine Life, a massive, decade-long effort to use the latest in electronic tagging technology to gather unprecedented information about oceangoing animals such as elephant seals, sea turtles and tuna.

Tracking salmon presents researchers with special challenges.

Radio tracking does not work in salt water, so the kinds of radio devices used on land and in fresh water are not practical. Instead, researchers have come to depend on information gathered by information-gathering ''archival'' tags. The tags can log a wealth of data, from temperature and depth to location, but must be physically retrieved.

The smallest salmon, smolts just entering the ocean, are the most vulnerable to their environment and the least capable of lugging around such tags. And even many of the fish that are large enough to carry them will never make it back to researchers.

As a result, little is known about the lives and pressures facing the most vulnerable salmon on their way to and from one of the world's most important fisheries.

''We can only learn so much from net sampling,'' said POST co-chair George Boehlert, director of the Pacific Fisheries Environmental Group of the National Marine Fisheries Service. ''Over the hundred years or so that people have been doing research on Pacific salmon, virtually all of it has been in fresh water. We know next to nothing about salmon in the ocean -- where they go, what they do.''

New technology has resulted in smaller archival tags, as well as acoustic tags, or ''pingers,'' which can be surgically implanted in fish as small as 4 1/2 inches long. The pingers communicate only the most basic information -- just enough to identify themselves and their locations -- and must be picked up by nearby sensors. Right now, such limitations make them impractical for open-ocean use.

But if an array of ''listening nodes'' were in place to receive the signals from the surgically implanted tags, scientists in theory would be able to eavesdrop on salmon migrations year after year. Salmon that are large enough could even be fitted with both archival tags and pingers to make it easier to find them to retrieve archived information.

The plan has received rave reviews in some quarters, though privately some biologists admit skepticism about its scope and cost. According to an executive summary, the array would cost about $10 million to put into place and require multiple sources of funding, cooperation among international scientific and commercial fishing communities, and collaboration between the governments of the United States and Canada.

''I understand people's skepticism, but the pieces are doable,'' Welch said.

Compared with the amount of money now spent on salmon research, Welch said, that $10 million for the array is a bargain. A single research vessel can cost between $5,000 and $10,000 a day. Archival tags, too, are expensive, and are often lost. The array would reduce the need for vessels and increase the cost efficiency of research by making it possible to retrieve a greater percentage of tags.

But first, researchers must show that the ambitious idea can work.

This spring, Alaska salmon biologist Jennifer Nielsen will head up a pilot project for the program along Cook Inlet. Her work will include testing new tags on fish in the Ninilchik River and Deep Creek in Ninilchik.

Nielsen, fishery supervisor with the U.S. Geological Survey's Alaska Science Center, said her team will tag spawned-out steelhead, known as ''kelts,'' using 25 archival tags and 60 acoustic tags so new that they have not yet been put on the market. Kelts were chosen for the research because of their size, because they tend to migrate downstream in large groups and because the fish are highly likely to return to the area for a second spawning, she said.

Nielsen is excited about the possibilities of using such technology to track salmon.

''I want to know what these critters are doing on their own, when they're not part of our harvest,'' Nielsen said.

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