Bycatch excluder devices producing a cleaner shrimp fishery
By Joel Gallob
Newport News Times
28th may 2004
Last year, the Oregon Department of Fish and Wildlife Department mandated that all Oregon shrimpers use bycatch reduction devices (BRDs) when they go trawling for Oregon's succulent pink shrimp.
Those devices, says ODFW biologist Bob Hannah, are a proven success and are an example of what can be done when the resource harvesters have taken an active role in finding ways to do their work with reduced environmental impacts.
Bycatch - the landing of unwanted marine life (usually a protected species or a non-permitted species) along with target creatures - is widely considered one of the biggest problems in the fishing industry. Both the Pew Commission on the Oceans and the U.S. Commission on Ocean Policy, which recently released blue-ribbon reports, found bycatch to be a common, major problem in U.S. fisheries. The U.N. Food and Agriculture Organization has said the same thing about many other fisheries worldwide.
Oregon scientists and shrimp fishermen have been working on reducing that problem in their sector of the industry. This year will be the second year the shrimpers have fished using BRD - devices fishermen helped design.
The shrimpers catch their prey using trawl nets with a fairly tight mesh, small enough so the tiny crustaceans won't escape. That small mesh size has been the key to the two types of BRDs that ODFW says have been shown to cut bycatch in a big way.
One type of excluder, the rigid grate, is composed of a grid of vertical bars, spaced roughly 1.25 inches apart, that let the shrimp pass between them while forcing larger fish up and out of the way of the waiting trawl net. It is called the Nordmore grate, named after a Norwegian who invented it. The other type is the soft-panel BRD, which does largely the same thing using a leading panel made of netting.
"Last year," said Hannah, "the boat count for Oregon was 59 (shrimping) vessels.” The pressures on the coastal fishing industry are revealed by the decline in numbers of vessels shrimping: in the late 1980s, the high was about 180 vessels.
This year is the first year in which Oregon shrimpers may be asked to bring at-sea observers along with them when they go fishing, he noted. So, there are no clear comparison numbers from past years to show any actual during-the-season bycatch reductions. But, said Hannah, ODFW has done test runs with the BRDs, and the results are clear. "We've eliminated more than 90 percent of the commercially valuable bycatch."
The BRD don't come without a penalty. The shrimp loss caused by the excluders in the experiments was quite variable, even between cruises testing the same excluder device. The Nordmore and the 3-inch soft panel device caused shrimp losses from zero to 10 percent. Interestingly, the larger devices produced higher shrimp losses, up to 15 to 31 percent. In some trials, the devices produced a higher average count per pound, indicating that larger, more desirable shrimp were also being excluded.
Still, the fishermen also benefit from the excluders. In some years, in some areas, the discard can represent a large part of the total haul. Sometimes, the unmarketable bycatch is so large that entire tows are dumped. With the success of the excluders, that should be a thing of the past.
The five-inch mesh showed only a 56 percent reduction in small rockfish, but excluded 97 to 100 percent of the large rockfish, 96-97 percent of the assorted roundfish.
Three trials of the Nordmore showed a 95 to 100 percent drop in bycatch of large rockfish; 60 to 80 percent in bycatch of small rockfish; 100 percent cuts in bycatch of adult whiting and large flatfish; and 80 to 90 percent drops in bycatch of medium-sized flatfish. "It wasn't that good for smaller bait fish," Hannah said, "fish like smelt. That was down by about 60 percent."
The 5-inch mesh BRDs, he continued, "have a somewhat lower effect for small rockfish, but they're still 100 percent for the larger rockfish."
There are other marine life forms besides those that people like to eat, and they, too, are part of our intricate marine ecosystems. One way of getting some idea of the effect of the excluders on them is to look at the reduction in total weight of bycatch. "The Nordmore grate," said Hannah, "decreased the bycatch by 75 percent in terms of the weight of all the bycatch. The 5-inch mesh cut it by 60 percent.” Further, the 5-inch mesh produced a 100 percent of the bycatch of skates and rays in the tests, and a 79 percent drop in catch of dogfish.
Hannah emphasized, "A lot of the work on this was done by the industry, by the fishermen themselves."
Brad Pettinger, administrator of the Oregon Trawl Commission and owner of the F/V Alex, and south coast fisherman Gerald Gunnari, owner of the F/V Coast Pride, have experimented with hinged aluminium grates for their fishing vessels. Jeff Boardman, president of the Newport Shrimp Producers Coop, "did a lot of experiments," Hannah said, seeking a cleaner shrimp fishery. Sara Skamser, owner of Foulweather Trawl in Newport, has also done a lot of experiments, he said, on how to separate target shrimp from bycatch species.
The trick has been to not only get the right size, but to develop a grate that won't bend when it is reeled up and soft excluders that don't get in the way on board.
"A lot of individuals did the work to get it to work for them," Hannah said. "We're now very clean by world standards for shrimp fisheries," he concluded.