Predator-prey interactions of American lobster (Homarus americanus) in the southern Gulf of St. Lawrence, Canada

Abstract

Between 1999 and 2006, predatorprey interactions of american lobster (Homarus americanus) in Northumberland Strait, Canada, and adjacent waters were evaluated from analysis of over 28 000 stomachs from 11 species of demersal fish, 5 species of pelagic fish, and 3 species of large decapod crustaceans. Predation on planktonic stages of lobster was rare and predation upon benthic stages of lobster was uncommon, principally restricted to shorthorn sculpin (Myoxocephalus scorpius) and cannibalism (during the moult). The diet of american lobster ≥40 mm carapace length during July-August consisted of rock crab (Cancer irroratus, 45-68% of prey biomass, of which c. 30% was moulted carapaces), small sea stars, and lobsters (0.7-12.9% of prey biomass, of which 70% was moulted carapaces). Molluscs, polychaetes, and fish remains (mainly bones and scales) each did not exceed 7.5% of prey biomass. A minimum of 35% of the lobster prey biomass was attributable to scavenging. With an average abundance of 7.6 kg ha-1, lobsters were the dominant demersal species captured in the study area. Lobsters largely avoided water >30 m deep and <6°C, and mud or muddy-sand substrates. © The Royal Society of New Zealand 2009.