The impacts of fishing on marine birds

Birds are the most conspicuous. wide-ranging, and easily studied organisms in the marine environment. They can be both predators and scavengers, and t hey can be harmed by and can benefit from fishing activities. The effects o f fishing on birds may be direct or indirect. Most direct effects involve k illing by fishing gear, although on a lesser scale some fishing activities also disturb birds. Net fisheries and hook fisheries have both had serious negative effects at the population level. Currently, a major negative impac t comes from the by-catch of albatrosses and petrels in long-lines in the N orth Pacific and in the Southern Ocean. High seas drift nets have had, prio r to the banning of their use, a considerable impact on seabirds in the nor thern Pacific, as have gillnets in south-weal Greenland, eastern Canada, an d elsewhere. Indirect effects mostly work through the alteration in food su pplies. Many activities increase the food supply by providing large quantit ies of discarded fish and wastes, particularly those from large, demersal s pecies that are inaccessible to seabirds, from fishing vessels to scavenger s. Also, fishing has changed the structure of marine communities. Fishing a ctivities have led to depletion of some fish species fed upon by seabirds, but may also lead to an increase in small fish prey by reducing numbers of larger fish that may compete with birds. Both direct and indirect effects a re likely to have operated at the global population level on some species. Proving the scale of fisheries effects can be difficult because of confound ing and interacting combinations with other anthropogenic effects (pollutio n, hunting, disturbance) and oceanographic factors. Effects of aquaculture have not been included in the review. (C) 2000 International Council for th e Exploration of the Sea.