Dietary Changes of Seabirds Associated with Local Fisheries Failures

Northern gannets Sula bassanus consume thousands of tons of pelagic prey in Newfoundland waters. To evaluate the hypothesis that harvests by seabirds and humans are similarly influenced by local fluctuations in prey availability, the annual catches of mackerel Scomber scombrus and squid Illex illecebrosus by gannets and humans over a 10-year period off northeastern Newfoundland were compared. Comparisons of annual fluctuations in the percentage by mass of different prey in the food loads of gannets with commercial fishery landings in nearby bays indicated that extreme reductions of dominant prey in the birds' diet were directly associated with subsequent local pelagic fishery failures. Dietary data collected from marine birds also provided information about the availability of prey that are neither commercially fished nor systematically surveyed.