Movement ecology of postspawning Alewife

Objective Alewives Alosa pseudoharengus are a culturally, ecologically, and economically important anadromous fish in the northwest Atlantic, yet their movement ecology remains poorly understood. This study was designed to examine mortality events and movement patterns of Alewives, including diel vertical migrations. Methods Using acoustic telemetry, we tagged 32 Alewives during their postspawning migrations through Passamaquoddy Bay (New Brunswick, Canada, and Maine, USA) toward the Bay of Fundy. Generalized additive models (GAMs) were used to examine the spatial distribution and timing of Alewife migrations through the bay. We also used GAMs to investigate occurrences of diel vertical migration in relation to tidal levels. Results Six of the tagged Alewives died during the study, with most mortalities occurring earlier in their migration within the river and estuary habitats, including four cases of endothermic predation: three in the estuary and one in the inner bay. Alewives were predicted to occupy three distinct spatial hot spots over time: the river and estuary during weeks 25–27, the inner bay during weeks 28–30, and the outer bay during weeks 31–32. Regardless of tidal height, the GAMs predicted that Alewives were deeper in the water column during the day (1200–2000 hours) and shallower at night (0200–0700 hours), with intermediate periods used to transition between these depths, indicating that Alewives undertook diel vertical migrations in the marine environment. Conclusions As Alewife populations continue to decline, this research highlights critical aspects of their postspawning movement ecology and underscores the importance of binational and multijurisdictional cooperation in the effective management of this species.