Commercial fishing produces a lot of bycatch, which is species other than the one being targeted.
Bycatch can be detrimental for the species, and it can be costly for commercial fishing vessels. If a boat scoops up too much bycatch, it has to dump its catch.
Off the coast of Oregon, shrimpers go after tasty, pink shrimp. However, they often scoop up a smelt known as eulachon.
Scientists from the Oregon Department of Fish and Wildlife may have a solution—LED lights.
“When we dumped our first tow with the lights up on the footrope, it was amazing,” said Bob Hannah of the DFW. “There was quite a bit of fish in one side with the shrimp, and the other side was basically nothing but fish. We did a few more toes and we moved the lights from one side, one net to the other, and every time we moved the lights to that side, all of a sudden the vast majority of bycatch didn’t show up in the net.”
The method was discovered by accident. Hannah said that the department had done some underwater camerawork to look at the behavior of the eulachon. They wondered what affect the camera light had on the fish and started conducting experiments.
Shrimpers have used other methods to limit bycatch, including smelt belts (sandpaper belts that shrimp slide down but the smelt catch on and are hauled out of the boat) and a grate system of vertical bars that sort the large fish out.
The working hypothesis about the effectiveness of the lights is that because the shrimp fishery works at deep depths, the fish avoid the approaching object.
“It’s been known for a long time that in the day and the night, fish react differently to the trawl,” said Hannah. “What we’ve shown is that by adding a light, you can alter the effect in a low light situation in terms of how they respond to the components of the trawl.”
The skipper of the test vessel ordered $2,000-worth of the lights before returning to shore with the scientists. He estimated that the lights, which could prevent having to dump up to 5,000 pounds of shrimp, would pay for themselves in a day.