Dynamics of Endangered Eastern Cape Breton Atlantic Salmon Populations

The eastern Cape Breton (ECB) designable unit (DU) of Atlantic Salmon Salmo salar comprises populations in 46 or more rivers in the eastern portion of Cape Breton Island, Nova Scotia, Canada. In 2010, the Committee on the Status of Endangered Wildlife in Canada classified the ECB DU as endangered. In support of recovery planning processes, we developed an integrated, statistical, life history-based model for evaluating the dynamics of populations belonging to this DU. Using maximum likelihood, the model was fitted to recreational fishery catch and effort data, fish counts by divers, intermittent mark-recapture data, and sparse age composition data for two populations in the DU. The model output included estimates of maximum lifetime reproductive rate ((alpha) over cap) and equilibrium population size-parameters that are important for determining extinction risk. The (alpha) over bar for the Middle River population (2.82 spawners/spawner) was double that of the Baddeck River population (1.39 spawners/spawner). These (alpha) over bar values would be considered low for Atlantic Salmon populations in general but are higher than those of populations in a neighboring endangered DU to the south. Slightly negative trends in recruitment deviates may indicate declining productivity in the two ECB populations; based on equilibrium analyses, neither population is expected to achieve the proposed recovery targets without an increase in productivity, survival, or both. Atlantic Salmon populations and habitat characteristics in ECB exhibit considerable diversity. Therefore, the dynamics of the Middle River and Baddeck River populations are unlikely to be representative of all populations in the ECB DU. Based on recent trends in recreational fishery catches, these two populations are likely among the healthier populations within the DU.