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<br />GGZ5J9 <br /> <br />both rankings (e.g., M/H). The information on Table 2 was not ranked by workshop <br />participants, and presented .as the sum of all life history stages. <br /> <br />Interactions with Nonnative Fishes <br /> <br />The geographic assessment of concerns for the presence of nonnative fishes <br />does not reveal the identities of the nonnative species or the type of threat posed to the <br />native species. However, much of this work has been done previously and is essential <br />for developing control strategies. Using information compiled from Hawkins and <br />Nessler (1991) and Lentsch et al. (1995), a table was prepared to indicate major <br />nonnative fish threats to listed species, the type of interaction, and the location that <br />provides the source of each nonnative species. The information in the table was <br />refined and expanded with the expertise of the participants (Table 6). <br /> <br />At least 20 nonnative species may have negative interactions with the listed <br />species. The riverine populations of most of these species are maintained by <br />reproduction in the river or escapement from ponds in the adjacent floodplain. Some <br />species are derived chiefly by escapement from reservoirs. Small mouth bass, <br />crappies, bluegill, green sunfish and northern pike, for example, have entered the <br />system from reservoirs in the upper part of the basin, and striped bass enter the system <br />exclusively from Lake Powell. Only trout are still stocked directly to the rivers of the <br />system below Flaming Gorge Dam. <br /> <br />Negative interactions occur primarily through predation or competition; predation <br />on eggs and larvae is particularly troublesome because it precludes recruitment. <br />Hybridization of the razorback sucker with the white sucker is a concern because white <br />suckers are known to hybridize with other native Colorado River suckers (Burdick <br />1995). <br /> <br />Nonnative Threats <br /> <br />Workshop participants identified numerous negative interactions, actual and <br />potential, between introduced species and listed species. However, not all interactions <br />were considered equally important. The relative importance varied according to the life <br />history stage of the listed species. White sucker and trout, both of which were listed on <br />Table 6, were not assigned a rank for the strength of negative interactions. Therefore <br />those species were deleted from further consideration. <br /> <br />Predation was the primary basis for ranking the negative interactions. In general, <br />the rankings for the Colorado squawfish and the razorback sucker were very similar <br />and will be discussed together. Nonnative predation on eggs and adults was regarded <br />as relatively minor. Threats to juveniles were typically less of a priority than threats to <br /> <br />28 <br />