A size-based approach to quantifying predation on longfin inshore squid Loligo pealeii in the northwest Atlantic

Cephalopods are primary prey to a wide range of predators in global marine ecosystems. Despite their apparent ecological importance, little information exists on size-based predation respective to this taxon. Using long-term food habits and data from population surveys and commercial landings, we quantified size-based patterns of predation respective to 11 species of finfish, elasmobranchs, and marine mammals over ontogenetic scales. General trends of sizeselective and seasonal foraging behavior are also presented for 25 species of predators from the northwest Atlantic Ocean. The functional role of squid was evaluated by contrasting patterns in sizebasedpredation between squid and fish prey types. Measurements of predator gape morphology and prey body depths ascertained if predators were physically limited when feeding on squid. Additionally, the amount of overlap between natural predators and the commercial fishing industry for squid size resources was estimated. Predation by finfish and elasmobranchs was generally focused on juvenile and sub-adult squid, while marine mammals primarily targeted adults. Consequently,marine mammals had the highest overlap with the commercial fishing indu&try for squid sizeresources. All predators exhibited size-selective feeding behavior, and trends persisted over seasonal time periods. Predators fed on a wider range of fish prey sizes than squid and did not appear to be gape limited when feeding on squid; however, large squid were not common in predator diets. Results suggest squid behavior and availability in the environment are paramount in shaping sizebased patterns of predation