Population Growth Responses of Blueback Herring to Dam Removal: A Simulation Study.

Nelson, Gary A.¹, Jon Honea², ¹Massachusetts Division of Marine Fisheries, Gloucester, MA, ²Emerson College, Boston, MA

Removal of dams has become an important restoration tool with the objectives of increasing abundance and spatial distribution of migratory fishes. Expansion into and benefits from newly-opened habitat will depend upon factors related to a species’ dispersal behaviors and the quality of habitat. Very little information on the Blueback Herring’s ability to recolonize newly-opened habitat is available in the literature. To that end, we developed a full life history, spatially-explicit, empirical-based, platoon-based simulation model for Blueback Herring in the Shawsheen River, MA to explore how adult dispersal behaviors and habitat quality may impact population abundance responses to newly-opened river habitat. We examined impacts of having preferences, where exploration might begin upon entering the river (mouth of river, head waters or homing to spawning/settling sites), Blueback Herring’s exploratory ability (distance searched in a day), spawner densities (spawners per m2) and habitat-related carrying-capacity on population growth responses. Results showed that the slowest population responses occurred when simulated Blueback Herring had habitat preferences, little exploratory ability, began exploration in the head-waters, had high spawning densities relative to juvenile carry-capacity, and juvenile habitat carrying capacities of upstream habitat were the same as downstream habitat. We conclude from our simulations that it will likely be difficult to predict population growth responses over time given lack of data on Blueback Herring’s dispersal abilities; however, a range of potential scenarios may offer some insight if unrealistic assumptions (e.g., no habitat preferences) are eliminated.