The investigators will conduct a model-based investigation of the dynamics of a productive pelagic ecosystems in the Gulf of Maine. The middle trophic levels in highly productive marine ecosystems are typically dominated by a few species of pelagic fish, such as sardines and anchovies in upwelling environments or herring and/or capelin in temperate and subpolar regions. These species act as important conduits for energy to higher trophic levels, including larger fish, seabirds, and cetaceans. When abundant, small pelagics can exert significant pressure on their prey, typically large mesozooplankton. Small pelagic fish exhibit complex dynamics and managing these species under an ecosystem approach is challenging. This modeling study will track both the abundance and condition of representative copepods (Calanus finmarchicus, Centropages typicus), herring, and bluefin tuna. The investigators will use a rigorous comparison of conditions from the 1980s and 1990s to develop the model. They will examine the sensitivity of this ecosystem to changes in fishing pressure on the middle trophic levels and to changes in the magnitude and timing of primary production. They will also consider the impact of increased temperature on the ability of C. finmarchicus to accumulate lipids and alter the condition of herring and tuna.
The project will lead to improved knowledge of ecosystems with productive food webs. It will also directly impact address issues related to the management of the herring resource in the Gulf of Maine. The investigators will examine the consequences of ignoring condition of zooplankton and fish, as is the case with the current stock assessment. They will also explore the dynamical properties of the model ecosystem and consider under what conditions it is possible to have both abundant and well conditioned herring.
