MEPS 184:303-307 (1999)  -  doi:10.3354/meps184303

Indirect effects of the availability of capelin and fishery discards: gull predation on breeding storm-petrels

Ian J. Stenhouse*, William A. Montevecchi

Biopsychology Programme, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X9, Canada

ABSTRACT: The Northwest Atlantic has undergone large-scale perturbations which have had profound effects on pelagic food webs. Over the past century, the increasing availability of human refuse and fishery discards have promoted the growth of Larus gull populations. During the 1990s, cold surface-water events have delayed the inshore movements of spawning capelin Mallotus villosus and fisheries closures have eliminated massive tonnages of discards. These circumstances have interacted to intensify food stress on gulls. We investigated gull predation in a large colony of Leach's storm-petrels Oceanodroma leucorhoa as an indirect consequence of the availability of prey and fishery discards. Predation did not differ between storm-petrels nesting in forest and open habitats even though gull nests were more often in close proximity to storm-petrel burrows in open habitat. In 1996 and 1997, gull predation on storm-petrels varied seasonally, with a significant decrease following the inshore movement of spawning capelin, a primary food that gulls consume and feed to their chicks. Capelin availability occurred considerably later in 1997, when gull predation on storm-petrels was greater and prolonged. The intensity of gull predation on storm-petrels appears to depend on the availability of spawning capelin inshore.

KEY WORDS: Indirect effects · Fishery discards · Capelin · Predation · Gulls · Storm-petrels

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