9539 - Laserfiche WebLink

Home Browse Search

in the Green River is intriguing, the ISMP catch rates of pikeminnow in 1998 and 1999 were lower than ~ the long-term average, with CPE in 1999 only slightly higher than in 1998. Colorado pikeminnow captured during removal efforts in 2000 was half that of 1999; however, ISMP catch rates for Colorado pikeminnow were higher than the previous three years of sampling. f In the Colorado River, during the fall YOY ISMP sampling for Colorado pikeminnow, the catch and catch rates of Colorado pikeminnow were not significantly greater during the NNC removal years than the long term average (1986-1997), or the recent pre-removal sampling years (1991-1997) (Figure ~ 18). However, the large increase in captures of Colorado pikeminnow in the treatment areas in 2000 was followed by a rise in ISMP catch rate that fall. Similar results were seen in a concurrent nonnative cyprinid removal study conducted in the ~ Colorado River near Grand Junction, Colorado (ISMP reach 2). Trammell et al. (2002) found only temporary reductions in nonnative abundance in treated backwaters. They observed no positive response in native fish abundance during the study or during ISMP fall sampling. Our ability to reduce nonnative cyprinid species appears to be limited to short-lived, site-specific reductions in abundance. However, the premise behind timing the removal to precede spawning of the endangered fishes was to provide a `window of opportunity' for early growth and survival of the endangered fish by removing NNC just as the endangered fish begin to occupy the habitats. We may have provided a short window of opportunity; we were able to deplete individual backwaters on a single f sampling occasion, although no long-term depletion was achieved of more than a few days. Although we could show little or no evidence of an immediate positive response on the part of native fish, this may be due to lack of appropriate sampling methods designed to test the response. Despite our inability to show either a reduction in abundance of NNC or a positive response from the native fishes, we should not abandon attempts to control these fishes. ~ The continuing presence of NNC in nursery habitats will remain a cause for concern for the long- term survival of the endangered fishes. The amount of effort expended on these studies was substantial, being both fiscally and labor intensive; several hundred thousand nonnative fishes were removed. But on ~ a different scale the effort was only moderate. Five weeks of effort per 30 to 50 miles of river reach, -18-