LED lights for bycatch reduction
A research study by the Oregon Department of Fish and Wildlife and Pacific States Marine Fisheries Commission has found that attaching of a series of LED lights to the fishing line of a shrimp trawl can significantly reduce bycatch.
The US West Coast Shrimp Fishery operates at depths of 50-150 fathoms where there is minimal ambient light. The fishery mostly uses double-rigged vessels, hauling two high-rise nets simultaneously, which makes for a very efficient research platform, as changes can be made to one net and not the other and the catches compared.
West coast shrimp trawls are fished with the net elevated about 15-24 inches above the sea floor, so there is a space for small fish to escape under the net, if they can be encouraged to do so.
This fishery has very low levels of bycatch, and all Oregon vessels (which make up most of the fishery) are required to use Nordmore-grate style bycatch reduction devices (BRDs) at all times with vertical bar spacing of just 19mm. The use of these BRDs had brought bycatch down to around 2% of total catch, but it was variable from year to year, and strongly influenced by the abundance of eulachon (small smelt species) from year to year.
Eulachon are listed as threatened under the US endangered species act, so eulachon bycatch reduction was still a priority.
The researchers put together a proposal to study if artificial lights could help reduce eulachon bycatch and it was funded by NOAA’s Bycatch Reduction Engineering Program.
ODFW Biologist Bob Hannah tells WF&A, “We hypothesized that if we made the rigid-grate more visible, more eulachon would avoid it and escape upwards out of the net; we also thought that perhaps making the fishing line more visible at the front of the net might also help, but we were less hopeful about that location.
“Well, the exact opposite of what we expected happened. Adding some lights to the BRD increased bycatch; somehow adding light at the grate encouraged eulachon to swim back through it and wind up in the codend; so we gave up on that.
“When we moved the lights to the fishing line of the trawl, we were amazed when we saw that eulachon bycatch dropped about 90% in the net with the lights; apparently the lights encouraged eulachon and most other small fishes to swim under the net and not enter the trawl at all.”
The study involved attaching 10 green Lindgren-Pitman Electralume LED lights to the centre third of the fishing line of FV Miss Yvonne’s two matched nets using heavy-duty zip-ties.
Each net was equipped with groundgear commonly referred to as ‘Newport Mud Gear’. The other side was fished without lights. The lights were spaced roughly four feet apart and pointed toward the centre, adjacent to the droppers. The lights were switched between the port and starboard nets periodically and a total of 42 tows were evaluated under a variety of conditions. Catch from each side was kept separate using a divided hopper and each was processed separately, weighing everything.
A complete analysis of the data collected is still ongoing, but preliminary findings show:
- Eulachon were reduced by 90.4% (by weight)
- Shrimp loss was 0.7% and was statistically non-significant, but variable
- Juvenile rockfish were reduced by 78.0% (by weight)
- Combined flatfish (slender sole, rex, arrowtooth etc.) were reduced by 68.8% (by weight)
The results were so dramatic that the researchers immediately encouraged all shrimpers to start using and testing the technique or a variant. Within two months, nearly every vessel in the fishery was fishing 10 green Lindgren-Pitman lights on the fishing line of each net, reporting very large reductions in bycatch of just about all species of small demersal fishes (except juvenile pacific hake), with very large reductions in eulachon.
Lindgren-Pitman’s LED Electralume has a battery life up to 500 hours, offering a consistent high intensity illumination that outperforms chemical light sticks – it lasts longer and penetrates deeper into the water to catch more fish.
The Electralume comes in a variety of colours including green, blue, aqua, purple, red, and white. A multi-coloured Electralume is also available and a full spectrum version that flashes every colour in the fish-attracting spectrum.
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