Easy solution for shrimpers and smelt alike

For the past four years, trawlers on the West Coast have been hauling in vast amounts of pink shrimp, much of it destined for dainty salads and shrimp cocktails across the country. But although these have been boom times for shrimpers, many are uneasy.

Along with pink shrimp, their nets often scoop up a threatened smelt called eulachon. Many shrimpers worry that the species’ vulnerability could lead to new federal restrictions on their industry.

Now scientists in Oregon seem to have hit upon an effective and low-cost solution: light up the nets. Last July, fisheries biologists Robert Hannah and Stephen Jones of the Oregon Department of Fish and Wildlife and Mark Lomeli of the Pacific States Marine Fisheries Commission chartered a shrimp trawler for an unusual experiment. The double-rigged boat, Miss Yvonne, drags a pair of socklike nets a foot or two above the dark seafloor. The researchers placed 10 battery-powered green LEDs at the mouth of one net, tying them to the “footrope” on its bottom side. The other net was unlit.

The crew made one trawling tow, dumped the catch from each net into a
divided hopper – and gaped in astonishment. On one side of the hopper, the haul from the unlit net held lots of silvery eulachon, flatfishes and other so-called bycatch mixed in among bright pink shrimp. On the other side, the catch from the LED-lit net was virtually nothing but shrimp.

“We couldn’t believe what we were looking at,” Robert said. Illuminating the net’s opening helped the eulachon dodge it. “They’re taking advantage of a little more light to see escape routes,” Stephen said. It is an all-too-rare example of a simple, affordable environmental fix that seems to produce instant benefits. Results of the Oregon researchers’ experiment, funded by a grant from the National Oceanic and Atmospheric Administration, will be published in a fisheries research journal. But already, the news has spread quickly through the state’s shrimping industry. “Within two months, the entire fleet was using these lights,” Hannah said.

In May 2010, the eulachon population from northernmost California to British Columbia was listed as a threatened species. The top culprits in its decline include fishery bycatch, dams and water diversions in the rivers where these forage fish spawn and climate effects on river habitats and ocean conditions.

NOAA is still considering protective regulations to rebuild the species. The tiny eulachon is the “elephant in the room” for the pink shrimp industry, Stephen said. Many fishers and processors “haven’t really realised what could be forced upon their fishery in the way of regulations.”

But science is rarely neat, and the eight-day experiment on the Miss Yvonne last year had a disastrous start. The exact placement of the LEDs proved critical. For the first two days, the researchers tried putting the lights around the grate in one net. They thought the illumination might aid the smelt in finding the net’s escape hole, but for unknown reasons, more eulachon swam past the grate into the net – doubling the bycatch. Flummoxed, the team moved the LEDs to the mouth of the net – and got their eureka moment.

After 42 tows, the researchers found that the illuminated net captured 90 per cent fewer eulachon than the regular trawl gear, but roughly the same amount of shrimp. The lights also significantly decreased bycatch of darkblotched rockfish, other juvenile rockfish and small flatfishes. NOAA plans to examine whether the trawlers’ measures to mitigate bycatch are sufficient, said Robert Anderson, the agency’s eulachon recovery co-ordinator. The illuminated net strategy looks “pretty promising,” he said.