REDUCE NEGATIVE IMPACTS OF NONNATIVE FISHES AND SPORTFISH MANAGEMENT ACTIVITIES. Fifty-two fish species occur in the Upper Basin, but only 13 of those are native species. Many of the nonnative fishes have been successful due to changes in the river system that favor their survival over that of native fishes. Competition with and predation by nonnative species is widely assumed to have played a role in the decline of the endangered fishes (Xxxx and Xxxxxxxx 1996). However, evidence of direct impacts of introduced species on native fishes is difficult to obtain (Xxxxxxxxxx 1981) and often is masked by human-caused habitat alterations (Xxxxx 1976). In studies on the Green River, researchers documented that young Colorado pikeminnow constituted 5% of the diet of northern pike, even though young Colorado pikeminnow made up a much smaller portion of the available food base in the river (Xxxxx and Xxxxxxx 1996). Researchers estimated that a single northern pike could consume 100 or more young Colorado pikeminnow per year. Also, northern pike are known to prey on adult Colorado pikeminnow, native roundtail chub (Gila robusta), flannelmouth and bluehead suckers, and may also feed on humpback chubs in the Yampa River. Colorado has completed a fisheries management plan for the Yampa River basin (a revision is pending). Smallmouth bass in the Yampa River have rapidly increased in abundance and pose a significant predatory and competitive threat to the endangered fishes. Recovery Program activities related to nonnative fishes initially focused on identifying impacts/interactions and developing nonnative fish stocking procedures. Nonnative fish control strategies were developed to identify and prioritize options for controlling or removing nonnative fishes from river reaches occupied by the endangered fishes as well as other reaches that serve as production areas for nonnatives that subsequently disperse into occupied habitat (Xxxx and Xxxxxxxx 1996; Xxxxxxx et al. 1996; Xxxxxxx and Xxxxxx 1991). In February 2004, the Recovery Program adopted a nonnative fish management policy that addresses the process of identifying and implementing nonnative fish management actions needed to recover the endangered fishes. Through 2006, emphasis has been focused on the control activities identified in these strategies. All nonnative fish control activities are being evaluated for effectiveness and continued as appropriate. The States and the Service also have developed final procedures for stocking of nonnative fishes in the Upper Basin (USFWS 1996a, 1996b). The p...
REDUCE NEGATIVE IMPACTS OF NONNATIVE FISHES AND SPORTFISH MANAGEMENT ACTIVITIES. The introduction, establishment, and proliferation of nonnative fishes is considered the primary threat to the recovery of four Colorado River large-bodied endangered fishes. Unfortunately, in the upper Colorado River basin, despite years of significant effort, the nonnative threat remains largely uncontrolled. Only 13 of more than 50 fish species that now occur in the Upper Basin are native (Bezzerides and Bestgen 2002). Over the last 100 years, native fishes have decreased in range and abundance, while introduced fishes have concurrently become more widespread and abundant (Xxxxxxx & Xxxx 1989, Xxxxxxxx et al. 1994; Xxxxxxxxxx & Bestgen 2002; Xxxxxxx & Xxxxx 2014). An increasing body of evidence characterizes the negative interactions of nonnative fishes with the endangered fishes (Xxxxxxx & Xxxxxx 1991; Xxxxxxxx 1991; Xxxxxxx et al. 1998; Xxxxxxxxxx & Bestgen 2002; Xxxxxxx & Xxxxx 2014), including predation and competition. Direct evidence of predation includes native fishes obtained from stomach contents of nonnative fishes (Xxxxxxx and Xxxxx 2014) and by visual observation of predation. Other means by which nonnative fishes may adversely affect native fishes are by competition for food and niche space. Warm water game fish, primarily stocked in reservoirs for recreational purposes, are thought to have the greatest adverse effect on endangered native fishes. Of those species, large-bodied predators are considered the most problematic – specifically centrarchids (smallmouth bass), esocids (northern pike), and percids (walleye). For example, during the 1990s, the Yampa River experienced a dramatic increase in northern pike and smallmouth bass numbers. Predation by these two piscivorous species wreaked havoc on the native fish community. Biologists documented significant declines of native fish densities in the Yampa River since that time (Bestgen et al.
REDUCE NEGATIVE IMPACTS OF NONNATIVE FISHES AND SPORTFISH MANAGEMENT ACTIVITIES. Fifty-two fish species occur in the Upper Basin, but only 13 of those are native species. Many of the nonnative fishes have been successful due to changes in the river system that favor their survival over that of native fishes. Competition with and predation by nonnative species (not including salmonids) is widely assumed to have played a role in the decline of the endangered fishes (Xxxx and Xxxxxxxx 1996). However, evidence of direct impacts of introduced species on native fishes is difficult to obtain (Xxxxxxxxxx 1981) and often is masked by human-caused habitat alterations (Xxxxx 1976). Recovery Program activities related to nonnative fishes initially focused on identifying impacts/interactions and developing nonnative fish stocking procedures. A nonnative fish control strategy has been developed to identify and prioritize options for controlling or removing nonnative fishes from river reaches occupied by the endangered fishes as well as other reaches that serve as production areas for nonnatives that subsequently disperse into occupied habitat. Through 2005, emphasis will be focused on the control activities identified in the strategy. All nonnative fish control activities will be evaluated for effectiveness and continued as appropriate. The States and the Service also have developed final procedures for stocking of nonnative fishes in the Upper Basin. The procedures are designed to reduce the impact on native fishes due to stocking of nonnative fishes in the Upper Basin and clarify the role of the States, the Service, and others in the review of stocking proposals. A memorandum of understanding has been signed by the States and the Service implementing the Stocking Procedures.
