What do you call thousands of dead and dying undersized fish, shoveled overboard from the decks of commercial fishing vessels? The industry calls it bycatch and literally tens of millions of juvenile or non-target fish, crabs and other animals fall victim to it each year. Now, a researcher with the Wildlife Conservation Society (WCS), working in cooperation with organizations in Alaska and the Pacific northwest, has discovered how to reduce this problem by up to 75 percent in the $6 billion walleye pollock fishery -- the largest fishery in the U.S. This is the first-ever pollock by-catch study performed under commercial fishing conditions.
Dr. Ellen Pikitch, director of fisheries programs for the New York-based WCS, has found that modifying the nets, called mid-water trawls, allows juvenile pollock, which would normally wind up as bycatch, to escape. Yet the number of market-sized fish (over 14 inches) retained remains virtually the same.
Her study is published in the latest issue of Fisheries Research, and reveals that nets using a single top-panel of mesh, instead of conventional fishing gear constructed of two overlapping layers, lets small pollock swim through the mesh openings.
This is a simple, very effective technique that s never been attempted before in the pollock fishery, says Pikitch. Allowing juvenile pollock to escape underwater rather than being brought on board and discarded could greatly enhance the survival and health of the resource, she adds.
The pollock fishery is the largest trawl fishery in the world. The U.S alone landed over 1.1 million metric tons in 1994, most of which were used for surimi, which is processed into products such as artificial crab legs and seafood flakes. In Alaska, bycatch of undersized pollock averages 10 percent of the total catch in number. Most is discarded overboard, but some is sold as low-value fish meal.
The North Pacific Council, a fisheries regulatory agency, recently ruled that beginning in 1998, bycatch of small walleye pollock can no longer be discarded overboard.
This ruling should provide a major incentive for the industry to adopt more selective fishing gear such as the kind our research team developed, says Pikitch.
Pikitch experimented with four different mesh diameters and types, finding that a square mesh panel measuring 3.8 inches was most effective in minimizing by-catch of small pollock, while retaining commercial-grade fish. When larger diameters were used, the number of marketable fish in the catch decreased. Diamond mesh, when pulled taught, sometimes formed narrow slits from which most small pollock couldn t escape.
During the study, single-trawl catches varied from a few hundred pounds to 79 metric tons. With catches over 40 metric tons, the nets became clogged with fish of all sizes, and bycatch was not reduced. Pikitch is currently studying methods to improve the selectivity of fishing gear for these high-volume catches.
Pikitch has worked on by-catch issues for the past 14 years, and was originally asked to do the study by fishing industry representatives after she gave a talk on the subject in 1992.
The impetus for the work came from the industry. No one wants to see fish wasted. There are many people in this industry who realize that wasting the resource imposes both economic and conservation costs. says Pikitch.
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