Each year millions of ocean creatures are killed or injured as a result of bycatch. Recent estimates show that for every four pounds of fish caught worldwide, fishermen throw away more than a pound (bycatch) of other marine animals. In shrimp trawls the ratio is fatally worse: for every pound of shrimp, four or more pounds of unwanted creatures die.
What happens to these unwanted animals once they are caught? They are usually tossed overboard either already dead or severely injured. Even fish of the target species that are an undesired sex, size or quality are often thrown overboard as bycatch.
A staggering 100 million sharks and rays are caught and discarded each year. An estimated 300,000 cetaceans (whales, dolphins and porpoises) also die as bycatch each year, because they are unable to escape when caught in nets.
Birds dive for the baited hooks on long fishing lines, swallow the bait (hook included) and are pulled underwater and drowned. Around 100,000 albatrosses are killed by longline fisheries every year and because of this, many species of albatross are facing extinction.
A Hell of a Problem
Bycatch is a serious environmental problem because valuable living creatures are wasted, food webs are disrupted, populations of endangered species are put at further risk, stocks that are already heavily exploited are further impacted and ecosystem alterations impact our ocean health worldwide.
High levels of bycatch usually results from the use of fishing gears that are not selective. This means that instead of adapting the fishing gear to catch a specific type of fish - the fishermen cast the widest net possible and cull through what they have caught - intended or unintended. It would be like going to the grocery store to buy a head of broccoli by bulldozing the entire produce section in order to do it. Or like hunting squirrels by clear-cutting the forest.
Different types of fishing practices result in different species being killed as bycatch: nets kill dolphins, porpoises and whales, longline fishing: kills birds, sea turtles sharks and fish. While bottom trawling can devastate entire marine ecosystems destroying the living structures on the sea floor (sponges, corals) that provide hiding, feeding and breeding areas for many important fish species. A single pass of a trawl removes up to 20 percent of the seafloor fauna and flora.
Longlines are fishing lines up to 40 miles long. Each longline can have from a few hundred to thousands of deadly hooks. They kill numerous fish and shark species as well as hundreds of thousands of endangered and threatened turtles, marine mammals, and sea birds each year.
The fishery with the highest levels of bycatch are shrimp trawl fisheries: over 80 percent of a catch may consist of marine species other than the shrimp being targeted. The bycatch of juvenile fish in shrimp trawls is a major problem caused by the small mesh used in shrimp nets.
There are several good examples in the U.S. and around the world where solutions to bycatch problems have been found, and implemented. Two examples are seabirds in longline fisheries and sea turtles in shrimp trawl fisheries. In some cases, seabird mortality from bycatch has been reduced by as much as 99%.
Many technical fixes exist to reduce bycatch. Turtle excluder devices are used in some shrimp fisheries to avoid killing sea turtle species. In the case of longline fisheries, the process of setting the hooks can be changed and bird-scaring devices employed which radically cut the numbers of birds killed.
To avoid catching dolphins in nets other devices can be used. Pingers are small sound-emitting devices attached to gill nets that deter dolphins, but they are not always effective. Escape hatches (consisting of a widely spaced metal grid, which force the dolphin up and out of the net) have been used effectively in some fisheries where they are required.
Although these devices may have a role to play, they cannot address the whole problem. Such devices need continual monitoring to check how well they work and assess any potential negative effects they may have. Realistically they will probably only be used in areas with well-developed fishery management and enforcement agencies.
Avoid fishing in bycatch hotspots
Gathering data onboard that quantifies when, where, and why bycatch is occurring gives fishery managers the information they need to close areas in which a high incidence of bycatch is taking place. These areas can then be closed during key time periods or destructive gear-types can be prohibited. Industry cooperation can also play a key role in reducing bycatch, in particular when vessels communicate with one another as they are fishing about areas to avoid because of high levels of bycatch.
On a global level, probably the only effective way to address the problems of bycatch is to control fishing. This will be best achieved through the creation of marine reserves, areas where NO fishing is allowed. In the case of highly migratory species such as seabirds and cetaceans, the only effective way of preventing bycatch is to discontinue the use of particularly damaging fishing methods and to close areas when vulnerable animals are present only reopening the area to fishing during times that the migratory animals are not there.