Étude de cas sur les impacts
Compétition: Introductions of non-native fishes can lead to the decline or extinction of native species through interspecific interactions (Moyle and Light 1996, in Hasegawa and Maekawa 2006). In particular, many species of salmonids have been introduced into streams throughout the world, primarily for recreational fishing (Fausch 1988, in Hasegawa and Maekawa 2006). Closely related native and introduced salmonids have not coevolved to partition niches, thus interspecific competition can often occur between such species (Krueger and May 1991, in Hasegawa and Maekawa 2006).
Using an artificial stream, habitat use by two sympatric native salmonids in the presence and absence of introduced salmonid species was investigated experimentally. When only native white-spotted charr Salvelinus leucomaenis and masu salmon Oncorhynchus masou were sympatric, they occupied different microhabitats. In the presence of introduced brown trout Salmo trutta or rainbow trout O. mykiss, however, white-spotted charr and masu salmon were observed to use a similar habitat and interspecific competition between white-spotted charr and masu salmon was initiated. The study suggested that the coexistence of native salmonids was negatively affected through interspecific competition between native and introduced salmonids.
Compétition: Several species of the salmon family and Rheophilous cyprinids are reportedly affected. The scale of impact of this species is weak.
Yosemite National Park (United States (USA))
Réduction de la biodiversité indigène: A study (Knapp, 2004), which used data collected during a census of native herpetofauna, non-native trout, and habitat characteristics at all lentic water bodies in Yosemite National Park, was undertaken to quantify the effect of trout introductions and habitat on the distribution of four amphibian species and two reptile species. Non-native trout which occupied 56% of habitats deeper than 4m were observed in 245 of the 2655 surveyed water bodies (9%). Gill net surveys indicated that brook trout (Salvelinus fontinalis) and rainbow trout (O. mykiss) were by far the most common fish species, with brown trout (Salmo trutta), golden trout (O. mykiss aguabonita), rainbow trout x golden trout hybrids, and Lahontan cutthroat trout (O. clarki henshawi) found only rarely (3 lakes each). The only other fish species encountered during the survey was an introduced population of Sacramento sucker (Catostomus occidentalis) detected at a single site.
The results of the current study provide strong evidence that in Yosemite National Park, introduced trout have profoundly altered the distribution of two mountain yellow-legged frog (see Rana muscosa in IUCN Red List of Threatened Species) and Pacific treefrog (Hyla regilla) of the four native aquatic-breeding amphibians (the other two being Yosemite toad (see Bufo canorus in IUCN Red List of Threatened Species) and Sierra newt (Taricha torosa sierrae) and both of the widely distributed garter snake species. Mountain garter snake (Thamnophis elegans elegans) and the Sierra garter snake (Thamnophis couchi couchi).