9375 - Laserfiche WebLink

Home Browse Search

estimate population size using sequential (year to subsequent year) Lincoln-Peterson estimates. All statistical analyses were run on the STATISTIX statistical package. Flow and temperature data were gathered by the United States Geological Survey (iJSGS) at the State Line gage and the Near Cisco, Utah, gage. River locations presented as river miles from the Green and Colorado rivers confluence and flow volumes have been presented in English units. All other units of measure are metric. RESULTS Reproduction and Early Life History Westwater Canyon and adjacent river reaches were sampled for young of year chubs and J sympatric species on 29 occasions over a five year period (Appendix Table 3). The majority of the sampling occurred in July and August of each year. Young of year chubs were collected in all years of the study. Of the project total (n= 3216 YOY), the greatest annual catch occurred the final year of the study (1996; n=1832) and fewest were collected in 1995 (n=92). Mean lengths of the Age 0 chubs were slightly larger upstream of Westwater Canyon than in the canyon (Table 2) during three of four years tested. In 1996, canyon-collected young of year were larger, and in 1995 there were too few YOY collected on any one sampling date to make a reasonable comparison. The only significant difference in sub-reach means occurred in 1994, the lowest flow year of the study (above vs within the canyon; F=1.49; d€136). Table 2. Mean total length of YOY chubs collected on select dates, 1992-1994, and 1996, above Westwater Canyon (RK 204 - 199.4) and within the canyon (RK 199.2 - 190.4). Sample size refers to number of individuals; p-value refers to significance of an analysis of variance between the sites. ABOVE CANYON CANYON Sample Date n mean length SE n mean length SE p 920721 75 23.773 .661 67 23.045 .623 .17 930802 420 16.881 .219 20 16.45 .812 .14 940712 137 20.051 .219 64 17.70 .262 .04 960815 258 27.643 .423 370 30.77 .333 .15 Hatching Dates /Spawning Period As mentioned in the Introduction, we were not able to determine spawning activity through the collection of adults in this study. However, we did try to characterize time of spawn through the collection of early life stages. Beginning in 1993, we started sampling for young chubs near the spring peak. We tried sampling with larval drift nets, larval light traps, and fine meshed seines. The only technique that proved successful were the small meshed seines. From those collections, days after hatch were calculated for the modal peaks (Table 3) in the Age O length frequency histograms. Spawning activity appeared to be bi-modal in 1992 and particularly in 1993 above the canyon. Hatching occurred later in the canyon than upstream, with the exception of 1996. 5