7025 - Laserfiche WebLink

Home Browse Search

10 Castleberry and Cech (1986) found that introduced arroyo chub Gila orcutti displaced native Mojave tui chub Gila bie%r mohavensis from its fluctuating habitat, a desert river. Arroyo chub had a longer evolutionary history in fluctuating stream environments than native tui chub. Tui chub probably existed in these habitats due to absence of similar fish. Arroyo chub maintained position and exhibited better swimming performance than native tui chub during flood events. Thus, differential responses to abiotic factors were important in the outcome of the biotic interaction. Interactions between native and nonnative fishes Trophic interactions Nonnative fishes can interact on a trophic level with native fishes in several ways. Nonnatives may directly decrease numbers of native fish by predation. The threat alone of predation may cause stress or behaviors in native fishes that are detrimental. Nonnative fishes may also compete with native fishes for food. If nonnative fishes are better able to catch or utilize a limited food resource, then native fishes may obtain less quantity or lower quality foods. Finally, a positive relationship may occur if introduced fishes serve as forage for native species. This interaction will be negative if the introduced prey has an anti-predatory defense that could harm or kill the native predator, especially if this defense is novel to the evolutionary history of the native. Predation. - Predation was :one of the most cited negative effects of nonnatives on native fishes. Although predation by nonnative fishes has contrIbuted to at least local reductions in populations of native fishes, it is difficult to demonstrate as a cause of species elimination (Moyle 1976). Because nonnative fish predation on endangered fishes is difficult to confirm in natural conditions, predation was documented most frequently on natives raised in large numbers, in confined areas, or after stocking. Most predators are opportunistic and will consume any prey available in large numbers. Many nonnatives in the upper basin are known predatory species and create an obvious concern. Of 37 native fishes from the southwestern United States, only four (10.8% of all species) are piscivores; of 57 introduced fishes, 26 (45.6%) are piscivores (Meffe 1985). They include egg, juvenile, and adult predators such as largemouth and smallmouth bass, green sunfish, northern pike, walleye, channel catfish, common carp, and mosquitofish. Because western fishes evolved with few predacious fishes, they may have a naivete towards predators and probably lack anti-predator traits (Minckley 1983; Meffe 1985). This is because they have been free 'of the influence of other major groups of fishes, especially the Perciformes for millennia. cMany introduced predators are also small' enough to infiltrate shallow backwater habitats that historically provided refugia from larger native piscivores (Meffe et al. 1983). ' The decline of Colorado squawfish and razorback sucker has often been attrIbuted to increased rates of mortality on early life stages by predation (Minckley 1983; Kaeding and j .;) ,;