While there are many fishing practices targeted for a commercial species, these methods also harvest a considerable amount of unintended marine life. Animals that are unintentionally caught because they are the wrong species, too small or the wrong sex are called bycatch, and are subsequently thrown back into the ocean dead or dying. Each year over 27 million pounds of marine life is discarded as bycatch from the world's fisheries. Thus, one in four animals caught die as bycatch, including species of marine mammals, turtles, seabirds and juvenile fish (Monterey Bay Aquarium).
Shrimp fisheries have been known for their high proportion of bycatch. In the Gulf of Mexico, for every pound of shrimp harvested, over ten pounds of other animals are killed (Monterey Bay Aquarium). This high level of bycatch has contributed to the decline of Gulf of Mexico reef fish populations such as snappers and groupers. Shrimp trawling was also responsible for high mortality rates among turtles, until the fishery was required to implement a turtle excluder device that acts like a trap door in the net for turtles to escape from. Even with this device, shrimp trawling still has a high incidence of juvenile fish bycatch (Lee). Catch of juvenile fish is extremely detrimental to ecosystems and fisheries, since these individuals die before they can reproduce or become commercially valuable (Monterey Bay Aquarium).
In the Northern Pacific, longlining is responsible for
high rates of seabird bycatch, which is threatening many species with
extinction. Seabirds such as albatrosses and petrels follow fishing boats
to scavenge for food, but often swallow hooks or become entangled in the
line which results in death. Researchers estimate that the black-footed
albatross cannot loose more that 10,000 individuals per year without causing
a decline in the population, but the bycatch from swordfish and tuna longlines
already exceed this limit. Overall, scientists believe that bycatch is
the most significant impact on albatross species (Audubon-Living