Seabird breeding performance during two years of delayed capelin arrival in the northwest Atlantic: a multi-species comparison

Breeding performance and timing of breeding of six seabird species breeding in the northwest Atlantic were compared during 1992 and 1993 when oceanogr aphic anomalies and changes in fishing practices provided an opportunity to compare effects of reduced food availability at a multi-species level. The inshore spawning migration of capelin (Mallotus villosus), a major prey fo r five of the six species considered here, was delayed by one month in 1992 and 1993, and a ground fisheries moratorium eliminated the production of f ish offal, an important alternative food source for Larus gulls and Black-l egged Kittiwake (Rissa tridactyla). Inshore, surface-feeding piscivores, ki ttiwake and Herring (L. argentatus) and Great Black-backed (L, marinus) gul ls, had lower breeding success than did pursuit-diving Atlantic Puffin (Fra tercula arctica) and Common Murre (Uria aalge). Breeding performance of Lea ch's Storm-Petrel (Oreanodroma leucorhoa), an offshore, surface-feeding pla nktivore, appeared unaffected by nearshore perturbations. Hatching, fledgin g and breeding success of inshore surface-feeders were much reduced while t hose of pursuit divers were similar to precious years when ocean conditions were normal. Later breeding in 1993 than in 1992 for kittiwakes and Herrin g Gulls resulted in more chicks of these species hatching after mature cape lin became available, dth subsequent higher breeding success. Results suppo rt the hypothesis that inshore surface feeders are more sensitive to change s in food availability than are pursuit-divers and offshore surface-feeders , and demonstrate the importance of timing of breeding in relation to tempo ral changes in prey availability.