8233 - Laserfiche WebLink

Home Browse Search

downstream of the Millard Canyon cobble bar (RK 53.9 / RM 33.5) were sampled with light traps and seines (refer to Appendix table 1). No Colorado pikeminnow larvae were collected below the suspected spawning baz. Two larval razorbacks were collected in these habitats. Red shiners dominated the light trap collections, however relatively few fish were collected overall (Table 2). Seine haul samples from this portion of the river were comprised completely of nonnative cyprinids with red shiners being the overwhelmingly dominant species. The ISMP database (1986-1996) was used to determine if YOY Colorado pikeminnow total length has varied longitudinally throughout Reach 3 (RK 193.2-0.0 / RM 120.0-0.0) on an annual basis. The contention was that if a consistent shift in size of YOY was found below Millard Canyon spawning may have occurred there. In figure 7, the average size of YOY pikeminnow collected above and below Millazd Canyon was plotted for eleven years: 1986- 1996. The respective means appear to vary little during the years of extended high spring flows; 1986, 1993, 1995. There was a greater discrepancy during the low flow years with the greatest difference in size of YOY pikeminnow observed in 1992 (YOY Colorado pikeminnow upstream of Millard Canyon averaged 36.4 mm TL; downstream averaged 49.7 mm TL). There was a statistically significant (t-test for unequal variances; p<0.05) difference in the size of YOY CPM collected above vs. below Millard Canyon in most moderate to low flow years (`87,'88,'89,'90,'92,'94,'96). However, there was no consistency to the nature of that difference, i.e., 3 of 7 years (42.8%) fish were smaller downstream of Millard Canyon with the converse occurring with a similar frequency (58.2% of the time). DISCUSSION Razorback sucker No adult razorback sucker were collected in 1994 or 1995. The lack of captures maybe an indicator of poor timing of sampling or insufficient effort to locate small groups of spawning individuals. The latter explanation likely applies to the razorback sucker sampling in the lower Green River. A comparison of ISMP generated captures of adult razorbacks in the middle (Reach 2 and 3) and the lower Green River (Reach 4) indicates razorback sucker densities are lower in the lower portions of the river (McAda et al 1997). The number of razorback sucker adults in the lower portion of the Green River is likely extremely low, perhaps an order of magnitude less than in the middle Green River. Occasional collections of adult razorback sucker continue to be reported in the lower Green River as referenced in Table 1. In the future, if collecting adult razorback suckers is deemed necessary by the RIP, sampling should become more innovative- employing different collection techniques (primarily fyke nets) and target new or infrequently sampled areas. Radio telemetry may also assist in locating spawning locations / more adults. Larval captures for all species declined from 1994 to 1995, which was exemplified by razorback sucker captures that fell from 44 to 4. A total of 210 flannelmouth sucker larvae were collected in and near the mouth of the San Rafael River in l 994. Similar sampling in 1995 produced 1821arvae. Bluehead larval collections declined from 210 in 1994 to 331arvae in 1995. The majority of flannehnouth sucker larvae were collected by early June, during both years. Bluehead suckers became abundant slightly later in the sampling periods. Total numbers 6