9555 - Laserfiche WebLink

Home Browse Search

Abundance of smallmouth bass in isolated pools was inversely proportional to abundance of native fishes. For example, mean native fish relative abundance in isolated pools averaged 16.7% (2.3 - 43.5 %, n = 10) of all fishes captured when smallmouth bass abundance was < 1 `% (mean = 0.2%), and was highest when bass were not found (Fig. 8). Native fish relative abundance averaged only 4.5 % (0 - 8.3 %, n = 4) when smallmouth bass abundance was > ] 0`%~ (mean = 22%, 11 - 31 %). Fathead minnow and white sucker abundance was also higher in isolated pools than the main channel, again perhaps indicating release from predation by smallmouth bass. These data suggested that native fishes and other small-bodied taxa could cohabit areas with smallmouth bass, but survived in higher numbers only when smallmouth bass abundance was quite low. Native fish abundance in isolated pools was still quite low compared to abundance in main channel Yampa River habitat as recently as 1999. Yampa River fishes, statistical comparisons.-The patterns of native fish presence or absence in the Yampa River based on descriptive data from the main channel and isolated pools were supported by logistic regression analysis. The probability of native fish presence in a sample was significantly higher if it was from an isolated pool than if it was from the main channel habitat (Table 7, Chi-square value = 9.30; p = 0.002); the large chi-square value indicates this was, by far, the largest effect. Probability of finding native fish in the sample was also negatively associated (Chi-square value = 4.50; p = 0.034) with the percentage of smallmouth bass in the sample. Solving the equation in the table, assuming for simplicity that the percentage of smallmouth bass was zero, predicted that the probability (as a %) of finding native fish in the sample was 69% if it was from an isolated pool habitat. That probability was reduced to 29% if the sample was from a main channel habitat. Probability of native fish presence in a sample was not affected by whether the sample was from a control or treatment reach (Chi square value = 0.19; p = 0.66). One would expect a positive and significant association of native fish presence with the treatment reach if predator removal was having a significant and positive effect on survival of native fishes. The year effect was significant but was dropped here, and for native fish abundance analyses (just below), because it only demonstrated that the proportion of habitat areas that supported native fish varied by year (2003, 16