Gear Shift: New Trawls and Concepts
by Fishermen's Voice staff

Trawl in a test tank. The controlled environment has advantages for testing. The conceptual leading edge is the use of net webs created with light that mimic nets. These herd fish into real nets without dragging bottom. Photo by Pingguo He, UNH

Redesigning trawl gear is seen as a leading edge approach in the effort to reduce bycatch on the way to truly sustainable fishing. One of the scientists in the forefront of gear design for the Gulf of Maine is Chris Glass, at the University of New Hampshire Sea Grant program.

In recent years a number of changes have been developed for groundfish gear. Most of these have involved the redesigning of trawl gear used as early as the late 1800’s. The changes to existing gear have reduced bycatch. But, said Glass recently, “habitat impact is a more important issue than bycatch reduction.”

Glass has been working on developing what he described as “almost futuristic” ideas for addressing habitat impact. He is developing techniques for trawling without scraping the bottom to herd fish up into a net. These ideas are, at this time, in the conceptual stage. It is the scraping of the bottom with gear, said Glass, that disturbs and can destroy where groundfish feed, breed and live. With less and less intact bottom on which to grow, there are just fewer fish.

Sea Grant at UNH worked with fisherman Carl Bouchard and Associated Fisheries of Maine to develop the Rope Separator Trawl. The redesigned trawl helps separate cod and haddock. Another trawl Glass worked to develop, and which won the Smart Gear competition in 2007, is the Eliminator Trawl. The Superior Trawl Company developed this trawl with Rhode Island Sea Grant researchers. Marine biologist and Glass colleague, Pinnguo He of UNH Sea Grant, devised a system that recombined net patterns, and used fish behavior data to sort out species. The net was a composite of the old cod end. A mix of square and diamond shaped mesh enabled the net to use the selective efficiencies of both designs.

Glass’ newest gear design ideas break away from the 1800’s model that most redesigned gear is based on and uses new technology, such as light and lasers, with data from fish behavior research gathered over recent years. Glass said that fish respond to visual stimuli from the presence of a net, not necessarily the physical contact. The net does not need to touch them in order for them to react.

The rope separator trawl separates fish fish that tend to seek the bottom from those that tend to swimm higher in the water column. The rope is strung horizontally across the opening of the net creating a visual hurdle. Drawing by Pingguo He, UNH

Earlier research by Clem Wardle of Scotland showed the relationships between gear and fish in the water. Wardle studied fish vision. The scales of a fish act like mirrors and he experimented with mirrors in the water to observe fish behavior. Reflected light signals fish and varied angles of that light has varied results. Fish use it to disguise their presence and read their surroundings.

From this Glass began thinking about the use of laser light to mimic the webbing of a net and create the illusion of a net. The light would stimulate the fish to respond, and then move in the direction of the actual net without gear making contact with the bottom.

Glass said there is a lot of scientific thinking that can be brought to fisheries management problems. However, a major concern for scientists working on gear development, is that within the standard management model, management seeks to reduce effort, rather than find sustainable uses of technology.

There is considerable difficulty, he said, in getting funding for research that looks for options that are off the beaten path. Most funding, he said, comes from answering a part of a problem, within a time frame that is useful to management.