Migration and apparent survival of postspawning alewife (Alosa pseudoharengus) in Minas Basin, Bay of Fundy

The anadromous alewife is a commercially fished clupeid in Atlantic Canada, whose oceanic migration is poorly understood. Few acoustic telemetry studies have been performed on this species as they are sensitive to handling, and are often compromised by surgical tag implantation. This research assesses the feasibility of a surgically tagging alewives using novel, V5 acoustic tags; first, a baseline assessment of short-term tagging effects was established based on reflex impairment and necropsies through a series of trials conducted in 2018-2019. Seventy-five adults were then tagged on their downstream migration in June 2019 following this protocol, and their migration tracked from the lower reaches of Gaspereau River into Minas Basin, Bay of Fundy. Alewives in the pilot tagging trials responded well to tagging, with low mortality (3%) and no observed instances of tag shedding 72 hours post-surgery. Water temperature and spawning condition had the greatest effect on the proportion of impaired reflexes following tagging. Within two days of being tagged, most alewives had left Gaspereau River and moved into the Southern Bight of Minas Basin. Macrotidal conditions prevailed in most of the study area, and tides moved alewives back and forth within the Basin in near-cyclical paths. Seasonal warming was associated with offshore movement down the spatial temperature gradient and into deeper waters. Offshore, larger tidal displacements widely dispersed tagged alewives through Minas Basin and to Minas Passage. Average time for migration through the study area was 28 d (SD +/- 2 d). Loss rate was 22% d-1 within Gaspereau River, decreasing to 1% d-1 in Minas Basin. Individual alewives were observed to make many transits through Minas Passage during their migration, where they may become exposed to in-stream tidal turbines.