Trout Responses to Stocking Rates and River Discharge within a Southeastern U.S. Hydropeaking Tailwater

Abstract

Freshwater fish populations often exist in systems characterized by novel ecological processes resulting from human alteration. Salmonid populations embedded within coldwater sections of warmwater rivers are spatially constrained by habitat availability. Tailwater fish contend with fluctuating river discharges and density-dependent processes associated with fish stocking and exploitation. Salmonid populations sustained through stocking versus natural reproduction may respond differently to changes in hydrologic patterns (e.g., hydropeaking) as well as declines in fish abundance. We assessed differences between stocked (Rainbow Trout Oncorhynchus mykiss) and naturalized (Brown Trout Salmo trutta) trout populations in Greers Ferry tailwater, Arkansas, regarding (1) spatial and temporal patterns of mean length, electrofishing catch rates, and relative condition following reduced number of stocked Rainbow Trout and (2) evidence that hydrologic characteristics and fish stocking intensity influenced relative condition. A 56% reduction in Rainbow Trout stocking did not result in systemwide change in mean length or relative abundance for Rainbow Trout or Brown Trout over the 16-year study period. Hydrologic variability, where river discharge spanned both reduced and elevated levels, positively influenced condition of both Rainbow Trout and Brown Trout. Assessment of survival of stocked Rainbow Trout may aid in further refining the timing and amount of stocking needed to sustain the population at a desired abundance. Further, assessing the influence of stocking fewer but perhaps larger (in terms of mean length) fish to meet management goals may be warranted. The persistent differences in relative abundance among river sections can inform management actions directed at Brown Trout, including harvest regulations. Such regulations may aid in reaching desired management goals, including abundance and mean length targets not observed after reduced stocking.Human alteration of riverine environments necessitates that fisheries managers work in systems with novel and often bounded ecosystem processes (Moyle 2014). Tailwaters, defined here as the area below impoundments characterized by hydrologic and thermal processes not persistent under unaltered river conditions, are one example of novel ecosystems that are managed to meet human needs, including for electric power production and recreational

Persisting in extreme environments: What are the drivers of body conditions of introduced fish in high mountain lakes?

“…The range of Kn values identified in this study was similar to those found for different salmonid species and ecosystems. For instance, Kn fluctuated between 0.78 to 1.19 for Alaskan salmonids (Trudel et al., 2005), between 0.87 and 1.01 for Oncorhynchus mykiss and S. trutta in southeastern U.S. rivers (Spurgeon et al., 2022), and between 0.72 and 1.2 for S. trutta in Pyrenean mountain lakes (Vives et al., 2005). However, in our study, individual body condition remained highly variable which is possibly controlled by diverse factors such as genetic, parasitism or social dominance (Filipsson et al., 2016; Winberg & Sneddon, 2022).…”