Accounting for food requirements of seabirds in fisheries management - the case of the South African purse-seine fishery

In South Africa, four of the seabirds that feed mainly on sardine Sardinops sagax and anchovy Engraulis encrasicolus have an unfavourable conservation status or a small population: African penguin Spheniscus demersus, Cape gannet Morus capensis, Cape cormorant Phalacrocorax capensis and swift tern Sterna bergii. Availability of prey is thought to influence their population size, but their food requirements have not been accounted for in management of the purse-seine fishery on sardine and anchovy. Means of identifying and attaining target populations of predators that are dependent on forage fish prey are discussed. Criteria used by The World Conservation Union to assess the conservation status of a species may prove useful in determining minimum viable populations, and the use of functional relationships in coupled models of predators and their prey may allow quantification of levels of escapement of prey that are necessary to maintain or rebuild populations of predators.