April 24, 2013
Commercial Fisheries and Marine Mammals
Dolphins and other marine mammals are threatened by boat collisions and entrapment
The U.S. government estimates that as many as 100,000 marine mammals are killed or injured by the U.S. commercial fishing industry each year. These deaths and injuries result from boat collisions, entanglements in fishing gear, and entrapments as non-target species (often called bycatch). Once entangled in fishing gear, small marine mammals drown. Large whales may be strong enough to swim off with nets of ropes from the fishing gear wrapped around them. This can cause infections or serious injuries that slowly lead to death.
Many types of fishing gear pose risk. Drift-netting involves miles of nearly invisible nylon nets set adrift in the sea for days at a time, entangling any animals that accidentally encounter the nets. Gillnets which are shorter invisible nets anchored to the bottom and equipped with floats so they stand up like an invisible fence, snare animals passing by. Longlines are, as the name implies, miles of line with thousands of dangling hooks. They have proven deadly to marine birds, turtles, dolphins and small whales that are attracted to the bait or the hooked fish. Even ropes used in lobster and crab pots pose a problem if the whale encounters the line with tail or flippers or head and becomes tangled as it thrashes.
Fisheries can also pose a different type of danger, for they may compete with marine mammals for the same fish and in the process reduce fish populations that marine mammals depend on for food. Salmon and other fish raised in net pens in the sea are fed pelleted food made from wild-caught fish. It has been estimated that it takes four pounds of wild-caught fish to produce each pound of salmon raised in these aquaculture facilities. The fish they are fed are small fish that are vital parts of the ocean food chain.
The loss of these fish populations can have a negative effect on the marine ecosystem. For example, the decimation of the Steller sea lion population in the north Pacific is attributed to the collapse of fish stocks the sea lions have depended on, stocks that have been heavily fished by certain Alaskan fisheries. Marine mammals cannot survive without a plentiful food supply, so overfishing by fisheries presents a real danger to the health of the marine ecosystem, especially when marine environments are also beset by pollution and other forms of habitat degradation.
The seal and sea lion populations on the west coast of the United States have responded positively to the protections they are afforded under the Marine Mammal Protection Act. Their relatively healthy numbers are perceived by the fishing industry, both commercial and recreational, as a growing threat to their business. Fishermen claim that seals and sea lions steal fish from nets and lines and also that they prey on salmon and sturgeon that fishermen are targeting. Otters are also accused of competing with fisheries for urchins, mussels and other shellfish. In these situations, fishermen have begun to ask that populations of seals, sea lions and otters be reduced to avoid the completion. Incidents of illegal shooting dolphins have also increased in the Gulf of Mexico as fishermen retaliate against dolphins they believe are stealing fish.
While it is true that some marine mammals have learned to take advantage of foraging opportunities provided by commercial and recreational fishing boats and to feed on fish waiting to pass through dams and locks at the entrance to fish spawning rivers, there are often non-lethal solutions to these interaction problems. In addition, the real cause of declining fish stocks is not the recovery of marine mammal populations but the growing human population. Too many people are moving to the coast and contributing to unsustainable habitat degradation and exploitation of resources including overfishing for commercially valuable fish. Scapegoating marine mammals is not a solution when the real problems are habitat-related or caused by overfishing by humans.