An experimental evaluation of competitive and thermal effects on brown trout (Salmo trutta) and Bonneville cutthroat trout (Oncorhynchus clarkii utah) performance along an altitudinal gradient

Abstract

Temperature-mediated competition (i.e., dominance shifts between species depending on temperature) may explain the segregation of salmonid species along altitudinal stream gradients. We evaluated this hypothesis for exotic brown trout (Salmo trutta) and native Bonneville cutthroat trout (Oncorhynchus clarkii utah) by rearing them in experimental sympatry and allopatry using enclosures constructed at six sites spaced along a 45-km segment of a mountain stream. For both species, we compared condition and growth between allopatric and sympatric treatment groups. We found that brown trout negatively affected cutthroat trout performance, whereas cutthroat trout failed to impart an effect in the reverse direction, regardless of temperature. Thus, we documented asymmetric competition between these species but found little evidence indicating that its outcome was influenced by temperature. Brown trout – cutthroat trout segregation is therefore unlikely to be due to temperature-mediated competition. Instead, brown trout may have displaced cutthroat trout from downstream areas through competition or other mechanisms, while abiotic factors preclude their (brown trout) invasion of upper elevations. Given the magnitude of effect observed in our study, we recommend that brown trout receive greater consideration in cutthroat trout conservation.

Asymmetric competition drives lake use of coexisting salmonids

“…Experimental manipulations of two larval anurans, Pelodytes punctatus Daudin and B. bufo, showed that Bufo individuals increased their use of the water column in the presence of the other, while Pelodytes did not change their space use (Richter-Boix et al 2004). Furthermore, the darter Etheostoma zonale (Cope) excluded Etheostoma olmstedi Storer from riZe and run habitats (Grey et al 2005), and exotic brown trout (Salmo trutta L.) displaced cutthroat trout from low-Xow areas in streams (McHugh and Budy 2005). Such eVects of competition may be best observed when new species are introduced, as revealed in our transfer experiment.…”

The potential influence of changing climate on the persistence of salmonids of the inland west

“…For example, native cutthroat trout in the interior West may be relegated to the highest elevation areas in the summer months to find suitable temperatures, and nonnative brown trout may occupy lower elevation habitats because of their tolerance to higher temperatures. An exception in this case may be Bonneville cutthroat trout that appear to occupy similar habitats to brown trout in larger rivers during warmer summertime periods (Colyer and others, 2005;McHugh and Budy, 2005). Where nonnative brook trout occupy similar habitats to cutthroat trout, similar shifts may occur.…”

Strategies for conserving native salmonid populations at risk from nonnative fish invasions: tradeoffs in using barriers to upstream movement

“…These mechanisms have been studied extensively in controlled laboratory and field experiments at small scales (see reviews in Fausch 1988, Dunham and others 2002a, Peterson and Fausch 2003b, but results are often difficult to generalize to larger spatial and longer time scales (Rieman and others 2006). An exception is experiments designed to explicitly consider environmental factors like temperature across a range of natural conditions, either in the field (McHugh and Budy 2005) or by simulating conditions in the laboratory (Taniguchi and Nakano 2000).…”