Bycatch

This chapter discusses the bycatch, incidental catch-ups and killing of aquatic animals by fishermen. Bycatches of marine mammals have probably occurred for as long as people have been putting nets and lines into the water. Most species of marine mammal that occur in places that are heavily fished have been caught in at least one type of fishing gear. Most types of fishing gear have been reported to ensnare marine mammals at one time or another. Some captures seem to defy reason. Large whales, for example, may become caught in a single lobster pot line, and porpoises can get caught in simple fish traps that they are able to find their way into but not out of. One estimate of global bycatch levels suggests that over 300,000 marine mammals per year are killed in fishing operations globally. Marine mammals generally reproduce slowly, and their populations are not able to withstand much additional non-natural mortality. The removal of just 1% of the population per year may be more than a marine mammal population can sustain in the longer term. Bycatch is recognized as one of the most important sources of anthropogenic mortality among many species of marine mammals. For this reason, many nations now legislate to protect marine mammal populations from deliberate or accidental exploitation, and there are several international agreements with the same aim. Legislation to protect marine mammals from excessive mortality has resulted from a variety of case studies that have uncovered unsustainable levels of incidental capture. Several of these cases have become widely publicized and have generated considerable public attention and debate. © 2009