Halibut Excluder Helps Hapless Halibut Escape Cod Nets
ANCHORAGE, Alaska -- It's called the halibut excluder -- a scary name for a nifty device, especially if you're a hapless halibut caught in a cod trawl net off Kodiak Island.
The island's fishermen are working with scientists and a custom net manufacturer to modify cod trawl nets so that halibut, gathered up with the cod, can swim free.
Four trawl fishermen were allowed to fish outside the regular season to test the device. While modifications are needed, the halibut excluder could fix a big problem known as bycatch -- fish that are unintentionally caught.
"If everyone used this you would expect the halibut bycatch to be cut in half," said John Gauvin, cooperative research coordinator for the Marine Conservation Alliance Foundation, which is working with commercial fishermen on the project.
Halibut is an important commercial and sport fishing industry in Alaska, with the largest concentration in the Gulf of Alaska near Kodiak. The catch limit in the gulf is 26 million pounds. They're often caught in nets for Pacific cod.
Fishermen are allowed a certain amount of bycatch but must stop fishing when they exceed the limit -- 2,000 tons of halibut each year. If that amount is exceeded, the fisheries are shut down -- no small matter for the approximately 100 trawlers working the gulf.
"No fishing, no money," said Mirek Lenda, a commercial fisherman who defected from Poland in 1987 and now makes custom fishing nets on Kodiak Island.
Pacific cod is the second biggest fishery in Alaska after pollock, bringing in $6.7 million for commercial trawlers in the Gulf of Alaska in 2005.
The halibut bycatch problem was so bad in the fall of 2004 and 2005 it shut down the gulf's cod and flatfish fisheries.
Kent Helligso, owner of the 79-foot trawler Pacific Star, said the shutdown also had the effect of temporarily putting many of the town of Kodiak's 6,000 people out of work. About 1,000 people are employed in the town's fish processing plants.
The halibut excluder works this way: The trawl net is fashioned with two large panels on the sides of the net about midway back with long, narrow slots for the halibut to swim free. Slots work well because halibut are a flat fish and can fit through the openings.
Cod have large heads making escape more difficult. The trick is finding the perfect slot size to keep the cod in and let the halibut out.
Fish biologist Craig Rose with the National Marine Fisheries Service helped design a prototype that had panels made from fiberglass rods. Commercial fishermen liked the idea but could see the prototype needed modification.
For one thing, the rods made the net too stiff to be wound on a net reel. The prototype also wasn't durable enough for commercial fishing.
"The fishermen looked at it and said we see what you are getting at but that is not going to make it in the real world," Gauvin said.
What developed was a real collaboration between the scientists, the commercial fishermen and Lenda, the net manufacturer, to come up with a workable excluder, Rose said. His agency provided information on fish behavior and equipment the fishermen didn't have such as specialized sonar and an underwater camera. The fishermen brought practical knowledge to the project.
The collaborative spirit extended to Kodiak's trawl fleet of more than 40 vessels. With Lenda's help, the fishermen got busy making their own excluders.
Lenda said the first task was to find affordable materials. He thought of the many piles of scrap cable piled around Kodiak Island. (The cable is used to attach sonar equipment to the top of the fishing nets.)
"All fishermen started looking around Kodiak Island," Lenda said. "It was everywhere."
Through a process of trial and error, a redesigned excluder was built that was about four times larger than the prototype. Each 38-foot long net had two excluder panels placed midway on the sides.
The first test was held last August. However, the fishermen couldn't find any cod.
Two months later, the scientists and fishermen tried again. Two trawlers made 14 tows each -- not enough to be considered a real test -- before bad weather cut the experiment short.
But only a few halibut were even trying to go through the slots.
"It surprised us because they could. They would swim by and not even try. It was frustrating," Gauvin said.
The team went back to the drawing board. One problem was that the water was flowing too fast through the excluder for the halibut to escape. The water needed to be slowed, creating an area where the fish would mill around.
Gauvin came up with the idea of putting 8-inch-diameter floats inside the excluder. They were tied loosely so that they would bounce around, creating a disturbance in the water for the fish.
"The halibut all of a sudden had a real interest in trying to get out," Gauvin said.
Testing continued in April on Portlock Bank northeast of Kodiak. Four boats completed about 23 tows each, this time a real test. The excluder reduced halibut bycatch by more than 50 percent. It also reduced the cod catch by as much as 30 percent.
Rose said researchers, the fishermen and the net manufacturer will be experimenting with different size slots and stiffer materials for the panels. The cod, with their bigger heads, can sometimes bend the cable and get out.
If the cod losses could be reduced to 5 percent, Rose said he would call the experiment a success.
"I would be declaring victory at that point," he said.
On the Net:
Marine Conservation Alliance Foundation: http://www.mcafoundation.org
Source: Associated Press