The influence of climate and prey availability on flatfishes on the Newfoundland Grand Banks

Abstract

Fishing and environmental variability interactively affect fish population dynamics, where fishing can increase population variability in response to environmental change. Therefore, developing fisheries management strategies that account for these interactions is necessary for managing recovering populations in a changing climate. Using a combination of ecological and population dynamics approaches, this thesis investigated the interactive effects of overfishing and environmental variability on yellowtail flounder (Limanda ferruginea) and American plaice (Hippoglossoides platessoides) populations on the Newfoundland Grand Banks, Canada. These populations were selected given their different recovery patterns following population collapse in the early 1990s, despite sharing similar life history characteristics, inhabiting similar environments, and having been managed under the same fishing moratoria. Specifically, the yellowtail flounder population recovered in four years, while the American plaice population has yet to recover 30 years after collapse. By coupling spatiotemporal models of bottom water temperature and population distributions, I revealed that variability in spatial population distribution was influenced by a combination of density-dependent processes and spatiotemporal variability in temperatures. By developing a novel statistical method to integrate stomach contents and bottom trawl research data to estimate prey dynamics I also showed that northern sand lance (Ammodytes dubius), an important forage fish prey species for American plaice, has exhibited oscillatory dynamics over time, which may affect the productivity of their predators. Furthermore, expanding on indications that American plaice population dynamics may be influenced by natural mortality, results from a metapopulation dynamics model identified that natural mortality was not a primary driver of juvenile dynamics following population collapse. Finally, through the development of a modeling framework to underscore the importance of incorporating various population and ecosystem processes in population dynamics models, I revealed that American plaice population dynamics were strongly affected by variability in recruitment and adult natural mortality over time and that both stocks were influenced by an integrated regional climate index. Overall, by coupling ecological and population dynamics research, this thesis adds to the growing base of research that indicates that understanding how fishing and the environment interact is necessary to produce ecosystem-informed management advice to identify appropriate rebuilding strategies for collapsed populations.