9360 - Laserfiche WebLink

Home Browse Search

ISMP backwater sampling evaluation abundance of those taxa was also underestimated. The ISMP density estimates for largemouth bass were about 1/3 (30 %) of DMR estimates. Similarly, density estimates for green sunfish derived from ISMP sampling were also about 1/3 (34 %) of DMR estimates. Detection and abundance estimation of centrarchids was not an original goal of ISMP sampling, and the technique does not appear to be useful for such. The ISMP sampling technique detected the presence of the three abundant non-native cyprinids in backwaters nearly 100 % of the time. The ISMP density estimates of those three species were biased low and were, on average, 66 to 79 % of DMR estimates. The ISMP and DMR abundance estimates for cyprinid species were positively correlated with each other at moderate levels (rZ = 0.42 to 79) which reflected some concordance between the two techniques. We also analyzed the relationship between the presence and abundance of centrarchid species and three non-native cyprinids and habitat variables. Largemouth bass and green sunfish were most common in backwaters that were relatively large, deep, and had cover. Red and sand shiner, and fathead minnow were ubiquitous in backwaters and their abundance was poorly correlated with habitat variables. We also discussed the efficacy of fish removal as a management technique to enhance rare fish species in the Upper Colorado River basin. A new, and likely more rigorous sampling protocol needs to be developed which will more reliably estimate the distribution and abundance of centrarchids in backwaters of the Colorado River in the Grand Valley. However, additional data and information is needed to develop a sampling program to effectively monitor centrarchid abundance. Key features of such a sampling program include identifying which parameters to measure, and then determining the desired level of accuracy and precision of those parameters. Only then can a sampling program iv