Effluent and waste from fish farms may damage wild fish, seals and shellfish. Fish farmers use tiny quantities of highly toxic chemicals to kill lice: one overdose could be devastating. So-called "by-catches", or the incidental taking of non-commercial species in drift nets, trawling operations and long line fishing, is responsible for the death of large marine animals and one factor in the threatened extinction of some species.
There is an estimated 50% mortality rate for turtles who mistakenly take bait intended for game fish and are cut free with damaged mouths or hooks embedded in their mouths. Drift nets accidentally drown seabirds and cetaceans, in addition to capturing turtles. Fishermen are reported to kill dolphins to preserve their own fish catch.
An average of one humpback whale has died each year in Hawaiian waters due to direct strikes by moving boats or entanglement in fishing gear. However, in 1996 there was a sharp rise in deaths, with the loss of eight humpbacks from encounters with human-created obstacles. The numbers for 1997 are expected to be equally elevated. Most fatalities happen to newborn calves and does not bode well for the recovery of this endangered species.