Bykill in shrimp trawls in some parts of the world can reach to up to 90 percent of the total catch. That means only 10 percent of the catch is kept and the rest, dead or dying, is discarded. Since enormous areas of the world's continental shelves are subjected to bottom trawling, reducing its impacts will require protection of some areas from trawling. This is the only way to maintain habitat types that are affected by trawling and ensure that the marine life they support does not disappear. The key is identifying the most important areas to replenish fisheries and maintain marine biological diversity.
Several studies indicate that while trawling devastates many species, it benefits some others.
One group that benefits is scavengers, including some starfish and hermit crabs, that are not killed by trawl nets. These hardy survivors feed on the other, more delicate animals that the trawl crushes or unearths from their homes within the seabed. While trawling may be beneficial for a few fisheries, without bans in some locations, many commercial fish species and other valuable marine life will be reduced or eliminated, and biological diversity and ecosystem functioning will suffer. Fisheries are declining and collapsing worldwide due to overexploitation and habitat destruction. In the United States and Canada we have seen the ecological, economic, and cultural devastation that results from the collapse of groundfish stocks off New England and Newfoundland.