MEPS 424:219-227 (2011)  -  DOI: https://doi.org/10.3354/meps08947

ABSTRACT: Mixed-species foraging groups are well known for a broad range of taxonomic groups. Explanations have focused around 2 primary mechanisms: anti-predator behaviour and maximising foraging efficiency. In the ocean, feeding assemblages can involve seabirds, fish, cetaceans, pinnipeds and combinations of these groups. Here we examine association patterns between North Atlantic minke whales and seabirds. Based on the unique feeding strategies of different seabird guilds, predictions were made on the relationship between seabirds and whales in joint feeding assemblages (who profits from whom). These predictions were tested by modelling the presence of a whale with seabird aggregations using logistic regressions, involving presence/absence of seabird guilds, group sizes and measures of diversity as explanatory variables. A strong positive relationship was found between the presence of a whale with a seabird aggregation and the presence and group size of auks, the only seabird group able to concentrate fish on their own. No other seabird guild was relevant in predicting the presence of a whale. This suggests that ‘beater’ or ‘pirate’ theory best explains the relationship, with minke whales taking advantage of prey concentrations generated by the feeding behaviour of auks, and other bird groups taking advantage of dead, stunned or scattered prey left by the whales.

KEY WORDS: Species interaction · Balaenoptera acutorostrata · Foraging theory