8185 - Laserfiche WebLink

Home Browse Search

4 I I I I I I I I I I I I I I I I I I I 3.0 RESULTS Flow and temperature ranges for the Green and Colorado rivers for the 5 years of sampling are presented in Table 2. Length-frequency histograms were developed for each reach (Figures A-I - A-6) to help identify the size range of the cohort and distinguish age-O from juveniles. From these histograms and from observations of individual fish afield, we determined that maximum sizes of age-O in fall and spring were 60 and 70 rom total length (TL), respectively, for 1987, 1988, 1990, 1991 and 1992 year classes; and 70 and 75 mm TL, respectively, for 1989 year class. Low flows and early warming in 1989 probably allowed for early spawning and an expanded growing season that resulted in larger age-O fish 3.1 REACH 3 - THE LOWER GREEN RIVER Reach 3 on the Green River extends from Green River, UT (RM 119.8) to the confluence of the Green and Colorado Rivers (RM 0). Backwater habitats sampled in this reach from 1987 to 1992 were an average 1.8 ft deep (n = 705). Backwater temperatures during fall sampling were typically ISC warmer than the mainchannel, and 2.30C warmer than the mainchannel during spring sampling. 3.1.1 1987 Year Class A total of 448 age-O Colorado squawfish were captured in the lower 50 miles of this reach in fall 1987, compared to 150 in spring 1988 (Table 3). Geometric mean CPE between these two periods decreased significantly (Student's 't', P>0.05) from 8.75 to 1.97/100 m2. This point estimator showed a 77% reduction in CPE of the 1987 year class of Colorado squawfish in the lower Green River between fall 1987 and spring 1988. Total number of fish captured decreased by 67% (448 to 150). The fish captured in fall averaged 34 mm TL, those captured in spring, about 6 months later, averaged 43 mm TL (Table 3). Average growth of age-O Colorado squawfish during the 6-momh winter period was 9 mm; most of the growth probably occurred during October 1987, which remained a relatively warm and mild month. A total of 4 juveniles were captured in this reach in fall 1987 and 4 were captured in spring 1988 (Table 4). No CPE statistics were computed, considering the small numbers of fish. Juveniles caught in fall ranged from 62 to 87 mm TL, while those captured in spring ranged from 86 to 104 mm TL. Distribution of age-O Colorado squawfish, as geometric mean CPE, in the lower 50 miles of this reach differed between fall 1987 and spring 1988 (Figure A-7). In fall, 97% of age-O squawfish were caught in backwaters above RM 25, with 60% within a 5-mile section between RM 25 and RM 30. However, during spring sampling, no age-O squawfish were found in backwaters between RM 25 and RM 35. The majority of age-O captured (81%) were found above RM 35, and 18% were found below this point. This indicated a downstream movement by age-O Colorado squawfish between fall and spring. However, sampling a 4-mile reach below the confluence of the Colorado and Green rivers yielded only 2 age-O Colorado squawfish, indicating that if wintertime emigration from the Green River occurred, fish were moving below this point and into Cataract Canyon or perhaps Lake Powell. 3.1.2 1988 Year Class A total of 1707 age-O Colorado squawfish were captured in the, lower 50 miles of Reach 3 in fall 1988. This resulted in a CPE of 48.6/100 m2. By the following spring 1989, CPE had decreased significantly (Student's 't', P>0.05) by 62% to 18.4/100 m2. Total number of fish captured decreased by 57% from 1707 to 739.