Aquaculture and Fisheries | Population Biology | Terrestrial and Aquatic Ecology | Zoology
Populations of anadromous alewife Alosa pseudoharengus and blueback herring Alosa aestivalis, collectively referred to as river herring, have declined in the Connecticut River. A hypothesis for why river herring have declined is that predation pressures have increased associated with recent increases in abundance of striped bass Morone saxatilis. Information on striped bass abundance, size structure, and consumption rates are required to test this hypothesis. This study was designed to provide estimates of striped bass population size in the Connecticut River during the spring migration season, via an intensive mark-recapture exercise and either an open or robust mark-recapture model. Striped bass were sampled between Wethersfield, CT and Holyoke, MA in May-June 2007 and 2008 by night-time boat electrofishing. All fish ≥ 300 mm TL were tagged with a uniquely-coded internal anchor FLOY tag. Reports of tagged striped bass were solicited from recreational anglers. Monetary rewards were offered for tag reports. Connecticut Department of Environmental Protection (CDEP) conducted a creel survey of the Connecticut River in 2008, providing estimates of angler catch of striped bass. A total of 662 striped bass was tagged in 2007. Anglers reported 34 tag recaptures and an additional 7 recaptures were made during electrofishing operations. A total of 535 striped bass was tagged in 2008. Anglers reported 23 tag recaptures, and an additional 3 recaptures were made during electrofishing operations. Population size was estimated in 2008 using a Schnabel mark-recapture model; 65,744 (95% CI = 2,434 – 109,573) striped bass ≥ 300 mm TL were in the Connecticut River between Hartford and the MA/CT border during May 2008. Estimates were unavailable for 2007 because CDEP did not conduct a creel survey in that year. The Schnabel model population size estimate is biased to an unknown degree due to violation of underlying assumptions of the model. However, this population size estimate will still serve as a valuable reference point for quantifying predation in the Connecticut River. Future efforts to apply an open population model will require a much more extensive tagging and recapture effort. Alternately, telemetry studies of striped bass movement could elucidate the magnitude and direction of bias in closed population model estimates.
Schultz, Eric T.; Davis, Justin P.; and Vokoun, Jason, "Estimating Predation on Declining River Herring: Tag-recapture Study of Striped Bass in the Connecticut River" (2009). EEB Articles. 21.