Computer tags help scientists track halibut

Posted: Sunday, March 24, 2002

ANCHORAGE (AP) -- For five months, the feisty 60-pound Pacific halibut with the nickname Lip roamed the Gulf of Alaska, its movements monitored by a tiny computer tag anchored below its dorsal fin.

In a project that could revolutionize the study of ocean use by important Alaska species like halibut and salmon, the fish was among half a dozen big flatfish successfully tracked from Resurrection Bay over the past 18 months during a test of new miniature technology.

On its travels to and from deep water, this halibut sniffed at the surface and plunged as deep as 1,600 feet. When it traveled farther offshore, it spent whole days swimming hundreds of feet up and down in the water column, followed by days of steady cruising, often about 1,000 feet down.

Then, out in the abyss, it found what passes for halibut bliss.

In what could be the first glimpse of mating by the species, the fish shot straight for the surface on nine occasions, rising 300 to 570 feet in minutes before plunging just as fast to its previous depth.

While no one knows for sure what the halibut was doing, observations of breeding flatfish in the Atlantic Ocean suggest that the fish probably soared in unison with another consenting piscivore, according to biologists from the U.S. Geological Survey in Anchorage.

''It's like a dance,'' said Jennifer Nielsen, supervisor of fisheries research for the USGS's local biological resource division. ''As a pair, they do like a spiral ascent. It's part of its breeding behavior. Nobody is quite sure why they do it.''

''Everyone has known for a long time that (Pacific halibut) go off the shelf in the winter to breed,'' added Derek Wilson, a fisheries biologist working with Nielsen on the project. ''But individual breeding behavior has never been documented before.''

The halibut study illustrates how miniature tracking technology and tiny computers have changed field research forever, enabling scientists to gather detailed information about where wild animals go and what they do in environments beyond normal human scrutiny. By attaching the devices to fish, especially salmon, scientists can begin to answer fundamental questions about habitat use in the deep sea, Nielsen said.

Funded with a $77,000 grant from the Exxon Valdez Oil Spill Trustee Council, the halibut project was aimed at testing 14 tiny pop-up satellite tracking tags as a way to identify critical marine habitat for any Alaska fish. Though previously tried on tuna and marlin, the technology had never been used this far north, Nielsen said.

As designed by Seattle-based Wildlife Computers, the 2-inch-long, bobber-shaped devices trailed behind the halibut on a tungsten wire, constantly recording water pressure, temperature and ambient light as the fish swam. Unless recovered first by a fisherman, the device corrodes the wire at a programmed time, floats to the surface and transmits its data to a satellite.

By registering the time of each day's sunrise and sunset, the tags could enable scientists to indirectly calculate the approximate latitude and longitude of fish.

The halibut study is only the beginning. Additional satellite tags will go on halibut this next season in the Gulf and Bering Sea. In separate projects using nonsatellite tags that store data in memory or give off beeps underwater, Nielsen and co-researchers Wilson, Phil Richards and Chris Zimmerman plan to start tracking coho salmon smolts from Ship Creek, as well as steelhead from the Ninilchik River and Deep Creek on the Kenai Peninsula.



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