Movements and Demography of Spawning American Shad in the Penobscot River, Maine, prior to Dam Removal

Abstract

We conducted a baseline study to better understand the migratory movements and age and spawning histories of American Shad Alosa sapidissima in the Penobscot River, Maine. The Penobscot River is currently undergoing a major dam removal project that is focused on restoring migratory connectivity and recovering diadromous fish populations including American Shad. This study addresses key data gaps for a previously unstudied native population of shad prior to restoration. A combination of radio-(n = 70) and acoustic telemetry (n = 14) was used to investigate the movements of migratory adult fish in 2010 and 2011. Scale-based analyses were used to assess spawner age and iteroparity. Radiotelemetry results indicated that few tagged fish (5-8%) approached the head-of-tide dam. Tagged fish exhibited three general patterns of movement in the accessible freshwater river habitat: use of the upper river reach, the lower river reach, or both. Mean freshwater residence time ranged from 9.1 to 14.0 d. Congregating fish were observed at two sites in the upper river reach and spawning activity was observed. Freshwater survival and survival to the estuary were at least 71%. This observed high survival was consistent with the estimated age and spawning histories of tracked fish, which indicated that 75-95% of the sampled fish were repeat spawners. Estimated age of adult migrants ranged from age 4 to age 9. Postspawning acoustic-tagged American Shad exhibited a series of prolonged upstream and downstream reversals upon entering the lower estuary. These movements have been previously unreported, and suggest that estuarine residency after spawning is important to osmoregulatory acclimatization for re-entry into salt water and the resumption of postspawning feeding activity.

A dam passage performance standard model for American shad

“…These parameter values were then randomly sampled for each year t and used to predict cumulative probability of arrival by American shad in the Penobscot River each day based on simulated ATUs. The ATUs used in this study resulted in spawning dates from late May through late July, which roughly correspond to dates from previous work in this system (Grote et al 2014a). As information about arrival in the system improves, these values can be tuned in the model, but this range was thought to be sufficient for the purpose of simulation as all phenological events were temperature-driven.…”

“…Latent dam-related mortality has been widely reported in salmonids in estuaries (Budy et al 2002;Schaller et al 2014, Stich et al 2015a and is likely to impact other migrating diadromous species. Likewise, impedance of migration at dams has the potential to restrict distribution within a catchment and access to spawning habitat (e.g., Grote et al 2014a). Dams may also influence population dynamics through delay.…”

A New Paradigm in Alewife Migration: Oscillations between Spawning Grounds and Estuarine Habitats

“…; Grote et al. ), have been reported as a means of reducing stress from osmoregulation or conserving energy on the marine migration (Bernatchez and Dodson ; Bendall et al. ; Hubley et al.…”

Dam Removal and Fish Passage Improvement Influence Fish Assemblages in the Penobscot River, Maine

“…Also, in 2016 a rockramp fishway was completed and operational at the Howland Dam (rkm 100), located at the mouth of the Piscataquis River, a major tributary. Before fish passage modification, there was either a vertical slot or denil fishway at each of these dams, which were used by some anadromous species such as Atlantic Salmon, but were largely impassible to others such as alosine fishes (Opperman et al 2011;Grote et al 2014).…”