The ecology of focal forage fish and its influence on marine predators

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The long-term objective of my research program is to investigate recruitment dynamics of key forage fish species and how these dynamics shape trophic and food web interactions in marine ecosystems of northern Canada. Unlike terrestrial systems, marine food webs are uniquely under “wasp-waist” control, whereby most energy is funnelled through a few forage fish species, making these species critical to energy flow. Capelin is the focal forage fish species that preys on many invertebrates and is in turn preyed on by most large predators (i.e., fish, whales, seabirds) in northern marine ecosystems and, thus, is often thought to mediate ecosystem-level changes. These short-lived fish species are characterized by high natural fluctuations in population size (~±40%), driven by annual variability in the number of individuals surviving to reproduce, or recruitment. Mechanisms underlying recruitment dynamics are often unclear, in part due to a lack of hypothesis-driven research. My first short-term objective is to investigate the bio-physical factors (i.e., prey and predator densities, temperature, salinity) underlying capelin larval survival in the Canadian Arctic, where the abundance of this sub-Arctic species has increased dramatically in the last two decades. Within coastal Newfoundland, I also will quantify the relative contribution of spawning habitats and regions to recruitment in coastal Newfoundland using cutting-edge otolith chemistry techniques to identify the natal habitat of spawning capelin. As most vertebrate predators rely on capelin as prey, my second short-term objective is to manipulate the costs and benefits of group foraging under varying prey and predator conditions, using an experimental approach, to reveal the behavioural mechanisms underlying niche partitioning. Additionally, I will investigate predator foraging responses of multiple species to changing prey regimes, along with multi-dimensional niche overlap. Simultaneously investigating predator-prey relationships, species interactions during prey capture and niche overlap of multiple marine predators under dynamic prey regimes will determine whether interactions among predators obscure predator-prey functional relationships, and provide insight into food web responses to varying prey biomass along with mechanisms underlying these responses. Several long-term data sets will be integrated with short-term hypothesis-driven research, forming the basis of inter-related, field-based student theses. Overall, this research program supports a high level of HQP (3 B.Sc. field assistants, 5 B.Sc. Honours, 5 M.Sc., 3 Ph.D.), and will enhance our ability to maintain the long-term productivity of northern marine ecosystems to sustain fisheries yields and conserve marine biodiversity under a changing ocean climate.