Reduced Streamflow Lowers Dry‐Season Growth of Rainbow Trout in a Small Stream

Abstract

A wide variety of resource management activities can affect surface discharge in small streams. Often, the effects of variation in streamflow on fish survival and growth can be difficult to estimate because of possible confounding with the effects of other variables, such as water temperature and fish density. We measured the effect of streamflow on survival and growth of rainbow trout Oncorhynchus mykiss in a small stream in northwestern California by manipulating the flow entering four of eight enclosed stream sections (9.0-15.3 m long) containing one pool and 2.5-4.0 m of upstream riffle habitat. In the four manipulated experimental units, we reduced inflow by 75-80% over a 6-week period in summer 2003. Flow diversion substantially decreased water velocity in riffle-pool transition areas but did not strongly affect habitat volume or water temperature. Fish in control units grew about 8.5 times as much as those in units with reduced streamflow; however, discharge manipulation did not affect survival, which exceeded 90% in both treatments. The input of invertebrate drift to pools within control units greatly exceeded the input into units with reduced streamflow; the concentrations of drifting invertebrates differed to a lesser extent between control and manipulated units. Managers concerned about salmonid populations in small streams should consider dryseason streamflow to be a key variable affecting fish growth.

Anadromy and residency in steelhead and rainbow trout (Oncorhynchus mykiss): a review of the processes and patterns

“…Larger residents require more space and tend to occupy faster and deeper water than smaller individuals, and streams that do not maintain sufficient flow are unlikely to support large, old, resident O. mykiss (Todd et al 2008). As an example, by manipulating stream flow, Harvey et al (2006) found that growth rates of O. mykiss were 8.5 times lower in reaches with reduced flow than in control reaches. This line of reasoning has led to the hypothesis that higher summer flows improve opportunities for feeding and development, thereby permitting the expression of larger and older freshwater residents ( Fig.…”

Causes and consequences of invertebrate drift in running waters: from individuals to populations and trophic fluxes

“…First, the time scale over which flow is reduced may be a critical determinant of whether behavioural drift increases. For instance, several studies have observed decreased drift flux and concentration across natural declines in flow (Leeseberg and Keeley 2014) or experimental declines over multiple weeks (Harvey et al 2006;Wooster et al 2016). Second, there is some evidence that taxa may respond in different directions to flow declines (James et al 2009;Kennedy et al 2014).…”

Impact of season-long water abstraction on invertebrate drift composition and concentration

“…These changes in the riverine and floodplain environments in turn have important impacts on river biota. Water abstraction can influence fish assemblage composition (Benejam et al, 2010) and the density and growth rates of sensitive fish (e.g., salmonids, Harvey et al, 2006;Lange et al, 2014). Water abstraction also has important impacts on benthic invertebrate assemblages.…”