Point-Source and Non-Point-Source Problems Affecting Seabird Populations

Industrial pollutant discharges and oil spills currently represent the principal point-source hazards to seabird populations. Several examples of severe disruptions to localized colonies include the near extirpation of brown pelicans and double-crested cormorants in southern California by DDT; gull, tern, and cormorant breeding failures caused by PCBs and dioxins in the Great Lakes; and major seabird“wrecks”after oil spills such as the Amoco Cadiz, the Exxon Valdez, or the 1990 Arabian Gulf spills. Runoff of agricultural chemicals may affect seabirds as point-sources because of localized discharge into the sea at river mouths. Other regional problems include predation and disturbance by introduced animals and humans. Non-point-sources of significant seabird mortality or breeding failure include entanglement in fishing gear (especially drift nets and long-lines), persistent organochlorine pollutants bioaccumulated through the food web, human predation (especially at breeding colonies), and plastic fragments (now globally distributed at sea). During the past three decades legislation and enforcement have made significant progress in reducing many of the point-sources affecting seabird populations, and several international treaties have addressed fishing, marine pollutants, and plastics. Seabird colonies adjacent to human population centers remain in jeopardy, however, especially from continuous human encroachment and land development. Accurate seabird population censuses and pollution monitoring are becoming important assessment methods, using seabirds as bio-indicators of environmental quality.