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.

Received June 10, 2013; accepted November 5, 2013

ACKNOWLEDGMENTS

Financial support was provided by the Nature Conservancy, the University of Maine, NOAA Fisheries, the U.S. Geological Survey Maine Cooperative Fish and Wildlife Research Unit, the U.S. Fish and Wildlife Service, and Brookfield Power. Black Bear Hydro Partners LLC, Dynegy, the City of Bangor Wastewater Treatment Plant, the Penobscot River Salmon Club, Cianbro, and the Pate family of Orrington all graciously granted us access to their property. We thank John Kocik, Graham Goulette, Jim Hawkes (NOAA Fisheries), Daniel Stich, Gayle Zydlewski, Matthew Altenritter, and Matthew Wegener (University of Maine) for their efforts installing and maintaining the Penobscot River acoustic receiver array. Alex Haro and Steve Walk loaned us valuable equipment and entrusted us with the U.S. Geological Survey electrofishing boat. Daniel Harrison and Joseph Hightower both gave generously of their time as reviewers, and their input greatly improved this manuscript. Sampling was conducted under University of Maine's Institution Animal Care and Use Committee protocol number A2011-06-05. Mention of trade names does not imply endorsement by the U.S. Government.