Effect of Turbidity on the Temporal and Spatial Utilization of the Inner Bay of Fundy by American Shad (Alosa sapidissima) (Pisces: Clupeidae) and its Relationship to Local Fisheries

Since 1750, a unique, directed fishery for American shad (Alosa sapidissima) has existed in shallow, turbid, mega-tidal embayments of the inner Bay of Fundy during summer and fall. Tagging experiments indicated that migrating shad consisting of intermixed, river populations from the entire Atlantic coast of North America occur there between June and October. Shad migration was counterclockwise around the Bay following the residual current structure. Presence and duration of the shad run in Cumberland Basin was a result of interaction between migration timing, turbidity, and temperature. Mean daytime swimming depth was related to tidal phase and turbidity. High turbidity (Secchi ) of the mega-tidal embayments apparently extends the preference zone for light intensity of ocean-feeding shad into surface waters (2–10 m), making them accessible to the local fishery.Key words: drift gillnets, shad migration, light intensity preference, swimming depth, mega-tidal, eastern Canada