Enhancement of Fish Feeding and Growth after an Increase in Minimum Flow below the Conowingo Dam

Abstract

A summer minimum flow requirement was instituted in 1982 for the Conowingo Hydroelectric Dam, Maryland, where no such requirement existed previously. The response of fish to this minimum flow was assessed by monitoring food consumption and condition factor of three abundant, downstream species (white perch Morone americana, yellow perch Percaflavescens, and channel catfish Ictalurus punctatus), and by comparing the values from before and after the minimum flow was established. We also compared growth rates of white perch before and after the minimum flow was established by back-calculating length from otoliths. We found that fish condition (weight at length) was significantly greater for all species in years when the minimum flow was maintained. Similarly, growth rate (length at age) was significantly higher after the minimum flow requirement was instituted. Changes in food consumption appear to explain the differences in growth, as fewer empty stomachs and greater food consumption occurred after the minimum flow was instituted. Changes in bent hie invertebrate abundance appear to explain the increase in consumption. These results suggest that fish may be subject to indirect effects of flow alteration that are propagated through the food chain.

Flooded flatheads: evidence of increased growth in Mississippi River Pylodictis olivaris (Pisces: Ictaluridae) following the Great Midwest Flood of 1993

“…This invertebrate increase likely derives from heightened soil-and vegetation-derived nutrient availability, the abundance of warm, slow-moving water, the associated algae blooms, greater areas of benthos, and greater habitat heterogeneity (relative to the pre-flood channelized river) (Finger & Stewart, 1987;Kwak, 1988;Ward, 1989;Knowlton & Jones, 1997). As in our fish, channel catfish (Ictalurus punctatus) exhibit augmented invertebrate consumption and condition following increased floodplain inundation (Weisberg & Burton, 1993).…”

Temporal variability of fish larvae assemblages: influence of natural and anthropogenic disturbances

“…These results are similar to those found for adult fish captured in the same period in the dam's catchment area . Similar to adult fish, the impact of dams in the ichthyoplanktonic community includes a reduction in larval abundance (Scheidegger & Bain, 1995), the suppression of growth rates (Weisberg & Burton, 1993), changes in the community structure (Bain et al, 1988) and a reduction in species diversity (Gehrke et al, 1995), clearly reflecting the impact of the dam in reproduction and recruitment (Agostinho et al, 2004a).…”

Contrasting life-cycle impacts of stream flow on two Chinook salmon populations

“…Variations in stream flow can affect water quality (Ebersole et al, 2001;Poole & Berman, 2001;Dahm et al, 2003;Ebersole et al, 2003;May & Lee, 2004;Miller et al, 2008), amount of drifting invertebrates (Townsend & Hildrew, 1976;Elliott, 2002;Boulton, 2003;Lake, 2003;Nislow et al, 2004;Harvey et al, 2006;Miller et al, 2007), and refugia available for rearing salmonids (Hardy et al, 2006). Studies have identified positive relationships between stream flow volume and a variety of fish population parameters including feeding and condition factor (Weisberg & Burton, 1993), population biomass (Nislow et al, 2004;Harvey et al, 2006), growth of individuals (Nislow et al, 2004;Harvey et al, 2006;AlonsoGonzález et al, 2008), migration survival (McCormick et al, 1998;Connor et al, 2003), and year class strength (Ricker, 1975;Scarnecchia, 1981;Elliott et al, 1997;Mitro et al, 2003). Studies have also identified negative relationships between stream flow volume and year class strength (Cattanéo et al, 2002;Smith, 2000;Jensen & Johnsen, 1999;Lobón-Cerviá, 2003) and Alonso-González et al (2008) demonstrated negative impacts of both floods and drought on juvenile salmonids.…”