Passage Efficiency of Alewife in a Denil Fishway Using Passive Integrated Transponder Tags.

This article focuses on evaluating the passage efficiency of a Denil fishway constructed to restore river herring (Alewife *Alosa pseudoharengus* and Blueback Herring *A. aestivalis*) populations blocked by a dam on the Lamprey River in Newmarket, New Hampshire. Using passive integrated transponder (PIT) telemetry from 2013 to 2015, the study found that passage success increased with fish total length and was higher for male Alewives than females of similar size, while Blueback Herring showed minimal use of the fishway. Passage success for Alewives returning at least one year after tagging was approximately 63–64%, but factors such as fishway saturation and diel movement patterns negatively affected overall passage. The study highlights that fishway selectivity may bias population data and recommends combining sampling below, within, and above fishways for comprehensive demographic assessments of migratory river herring populations.