EXPLAINING VARIATION IN AMERICAN LOBSTER (HOMARUS AMERICANUS) AND SNOW CRAB (CHIONOECETES OPILIO) ABUNDANCE IN THE NORTHWEST ATLANTIC OCEAN

• Main Author: Boudreau, Stephanie Anne
• Other Authors: Department of Biology, Doctor of Philosophy, Richard A. Wahle, Hal Whitehead, Heike K. Lotze, Sandra J. Walde, M. John Tremblay, Boris Worm, Received, Yes
• Language: English
• Published: 2012
• Subjects: Local ecological knowledge; American lobster; Gulf of Maine; Ecosystem effects of fishing; Atlantic cod; Decapods; Lobster; Crab; Trophic-cascades; Ecosystem effects; Anthropogenic effects; Species interactions; Predation; Climate; Snow crab; Meta-analysis; Northwest Atlantic Ocean; Top-down interactions; Time series analysis; Fisheries; Ocean temperature; Canada; atlantic cod; Chionoecetes opilio; North Atlantic; North Atlantic oscillation; Northwest Atlantic
• Online Access: http://hdl.handle.net/10222/14603

In this thesis I assessed the causes of long-term changes in two large, commercially important decapod crustacean populations, American lobster (Homarus americanus) and snow crab (Chionoecetes opilio), in the northwest (NW) Atlantic Ocean. By combining available time-series data, including commercial landings, research surveys, and local ecological knowledge (LEK), I explored the causes of an observed ecosystem shift in the NW Atlantic (~1950–2009) which entailed a region-wide decline of groundfish and an increase in benthic invertebrates, including these decapods. Three hypotheses were examined to explain the increase in decapod abundance: (1) the predation hypothesis, whereby a decrease in predatory groundfish led to an increase in their decapod prey (top-down effects); (2) the climate hypothesis, whereby changes in temperature or other climatic variables helped to increase decapod numbers (bottom-up effects); and (3) the anthropogenic hypothesis, whereby changes in fishing pressure drove decapod population dynamics. I explored these hypotheses separately for lobster and snow crab, which may experience different ecological and commercial pressures. First, I investigated the interactions between predatory groundfish and lobster in the inshore region of southwest Nova Scotia. Long-term fisheries-independent abundance indices for lobsters and their predators are available for Gulf of Maine (GOM) waters in the USA, but not in Canada. To address research gaps I designed and executed a survey to collect the LEK of lobster fishermen fishing in the Canadian GOM. Forty-two fishermen were interviewed. Corresponding survey results from the USA were compared to the LEK results. Both sources provided evidence for a top-down effect (predation release), contributing to observed increases in GOM lobster abundance and landings. Second, I explored relationships between lobster abundance and landings in the NW Atlantic as they may relate to temporal changes in predators, temperature, climate (North Atlantic Oscillation Index, ...