Predation and competition: The impact of fisheries on marine-mammal populations over the next one hundred years

We discuss the potential for commercial fisheries to adversely impact ! I p opulation of marine mammal by the end of the 21st century. To a large degre e, patterns over the last 50 years regarding human population growth, succe ss and failure in marine-fisheries management, and life history and status information on marine mammals are the basis for 6 predictions. First, annua l worldwide landings of fish and shellfish by the end of the 21st century w ill be less than 80 million tons. Second, virtually all of the predictions regarding species composition and energy flow within a marine community, ba sed on models developed to date with incomplete information on species abun dance, food habits, genetic effects of fishing, and variability of predator food habits, will prove wrong on a decadal or longer time scale. Third, th e most common type of competitive interaction between marine mammals and co mmercial fisheries will be that in which commercial fisheries adversely aff ect a marine-mammal population by depleting localized food resources withou t necessarily overfishing the target species of fish (or shellfish). Becaus e of this, the number of extant populations and species richness of marine mammals will be reduced by the end of the 21st century, and coastal populat ions and species will be affected more negatively than will noncoastal spec ies. Fifth, predator control programs designed to reduce local populations of marine mammals will be common without changes in existing forms of fishe ry management. Finally, protein from marine mammals will become a more impo rtant component of the human diet than it currently is.