TRENDS IN PELAGIC FISH POPULATIONS OF THE SALDANHA BAY-REGION, SOUTHERN BENGUELA UPWELLING SYSTEM, 1980-1990 - A PREDATORS PERSPECTIVE

Changes in monthly and annual prey species composition of African peng uins Spheniscus demersus are described from 1 454 stomach samples coll ected from two breeding islands in the Saldanha Bay region of the sout hern Benguela upwelling system between 1980 and 1990. The diet was dom inated by anchovy, although pilchard, horse mackerel, round herring an d chokka squid were also taken. The relative abundance of anchovy in p enguin diet was highest between 1984 and 1989, coinciding with a perio d of favourable environmental conditions for recruitment of anchovy an d a subsequent increase in fish biomass. The more recent decrease in d ietary abundance of anchovy and its partial replacement by pilchard is consistent with independent (ship-borne acoustic) evidence of a recen t increase in pilchard biomass. In contrast to these congruent trends, the size of anchovy taken by penguins between 1980 and 1990 has decre ased dramatically, across years of good and poor recruitment. The reas ons for this remain obscure but may reflect, in part, poor recruitment of anchovy in the latter part of the decade. Monthly changes in the s ize frequency distribution of anchovy consumed by penguins apparently reflect seasonal patterns of fish migration.