We collaborate with the Consortium for Wildlife Bycatch Reduction to research and develop new and innovative fishing devices and methods that reduce the threat of bycatch to sea turtles, large whales, sharks and other marine animals.
Evaluation of Alternatives to Destructive Gillnet Fishing
Bycatch in gillnets is a major threat to endangered marine mammals, turtles, and other non-target species. Gillnets are entangling nets of uniform mesh size that are hung vertically in the water column with the aid of a weighted “lead line” on the deeper end, and a buoyant head rope closest to the water surface. Because gillnets are a widespread method of fishing around the world, it is critical that we find methods that significantly reduce this bycatch.
In the 1990s, the New England Aquarium conducted an experiment showing conclusively that acoustic pingers reduced bycatch of harbor porpoise to almost zero. Another potential approach involves altering the chemistry of the net. With funding from the Lenfest Ocean Program, the New England Aquarium is evaluating gillnets made with a small percentage of barium sulfate in several fisheries, beginning with the artisanal croaker fishery in coastal Argentina.
Sharks are frequently caught as bycatch by commercial and recreational fishermen. Since some sharks show an aversion response to certain electropositive metals, we are working with several different types of electromagnetic elements to evaluate their potential as shark repellents for fishing gear.
We have completed initial studies, which tested the reactions of captive spiny (Squalus acanthias) and smooth (Mustelus canis) dogfish to two metals—a lanthanide/cerium alloy (mischmetal) and a rare-earth magnet (neodymium-iron-boride). Dogfish are small, coastal sharks that are frequently captured as accidental bycatch in hook-based New England fisheries.
Over a period of two months, we tested how each species responded to the various baits and metals. In each species-specific trial, we presented animals with squid-baited fake hooks. Each fake hook was “protected” by either the mischmetal, the magnet or an inert decoy (e.g. stainless steel). We ran tests under a variety of conditions in order to test the effects of hunger and shark density on the bait selectivity of each species.
We have not yet completed our statistical analysis, but initial data suggests that the repellent effects of each metal will likely vary from one species of shark to another. The spiny dogfish were more averse to the mischmetal, while the smooth dogfish was more discouraged by the magnet. Both species were less likely to be affected by the repellents if they were hungry, and neither species was affected by the density of sharks in the experimental tanks.
These initial results suggest that metallic repellents may help reduce the bycatch rate of specific shark species, but their repellent qualities may be too specific to work with all species of sharks. Additional research is needed to better understand how other species of sharks respond to these and other metallic substances.
Fishermen use ropes to set gillnets and for tying lobster pots together and to buoy lines. This gear presents a hazard to whales, sea turtles, and large fishes that become entangled in the ropes.
The critically endangered North Atlantic right whale, in particular, has a long and tragic history of fatal entanglements with ropes used in the commercial fishing industry, and approximately 70% of right whales alive today bear scars from past entanglements.
We are working to reduce this threat by undertaking collaborative research with the fishing industry to evaluate potential solutions, including new ropes:
- Highly durable, sinking groundlines for trap fisheries that stay at or near the ocean bottom, decreasing potential conflicts with whales in the water column.
- Ropes manufactured strong enough to use as vertical lines in pot fisheries but that break under the pull of an entangled large whale.
- Vertical lines designed to be more visibile to large whales.