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

Abstract

AbstractPopulations of river herring (Alewife Alosa Pseudoharengus and Blueback Herring A. aestivalis, collectively), once abundant in coastal rivers along the Atlantic coast, have seen precipitous population declines, likely due to many factors, including commercial fishing, habitat degradation, and dam construction. Efforts to restore populations include the construction of fishways at dams, but upstream passage success of fish through fishways is variable. To evaluate passage efficiency of a fishway on the Lamprey River in Newmarket, New Hampshire, Alewives were PIT tagged in 2013 (n = 621) and 2014 (n = 501) and antennas monitored fish in 2013–2015. Potential handling effects, diel movement patterns, and fishway saturation negatively affected passage success. The probability of Alewives successfully passing through the fishway into the river above the dam increased with total length. The estimated probability of passage success of an Alewife of mean total length (280 mm and 292 mm for males and females, respectively) that migrated back to the dam at least 1 year after tagging was 0.63 for males and 0.64 for females. Fishway selectivity presents a potential bias in data collection in freshwater systems, and our results suggest that sampling below a fishway should be coupled with data collected from within and above the fishway for a more complete demographic sample of the migratory population.