8175

• UCREFRP Catalog Number: 8175
• Author: Converse, Y. K., L. D. Lentsch and R. Valdez.
• Title: Evaluation of Size-dependent Overwinter Growth and Mortality of Age-0 Colorado Pikeminnow.
• USFW Year: 1999.
• USFW - Doc Type: Salt Lake City, Utah.
• Copyright Material: NO

discharge in spring preceding fall collection offish, and average flow for summer (average from
July I to September 30) and winter (average from October 1 to March 31) period. Four stepwise
multiple regressions were performed (SYSTAT, Inc. 1997) to determine relationships between
flow and temperature characteristics with 1) age-O fish size in fall; 2) relative abundance of age-O
fish in fall; 3) age-1 fish size in spring; and 4) relative abundance ofage-1 fish in spring.

RESULTS

Evaluating overwinter size-selective mechanisms

Age-O length and relative abundance
For age-O year classes examined from fall of 1987 to spring of 1995 in the lower Green
River (Valdez and Cowdell 1996), 6,230 age-O Colorado pikeminnow were caught in fall, and
2,618 age-l fish were caught in spring (Table 1). Mean minimum length ofthe eight years was
20 and 28 mm for fall and spring, respectively, and mean maximum length was 60 and 70 mm
for fall and spring, respectively. For age-O year classes examined from fall of 1989 to spring of
1994 in the middle Green River (Valdez and Cow dell 1996), 1,348 age-O fish were caught in fall,
and 414 age-1 fish were caught in spring (Table 1). Mean minimum length of the five years
examined was 25 and 31 mrn for fall and spring, respectively, and mean maximum length was 59
and 63 mm for fall and spring, respectively. The 1994 year class was eliminated from further
analysis because ofnonnormality. Catch rates recorded as CPE are reported in Appendix 1.

Table 1. Summary of young Colorado pikeminnow sampling in the Green River over 8 seasons.
n = number of fish, Min = minimum length, Max = maximum length and X = mean length.
Fall Spring
Reach Season n Min Max X n rom max X
Middle 89-90 61 28 59 41 25 34 61 44
90-91 281 28 60 42 47 35 68 50
91-92 526 21 58 38 184 27 60 43
92-93 175 26 60 42 73 29 68 47
93-94 305 21 59 36 85 29 58 40
Lower 87-88 448 23 55 34 127 30 69 43
88-89 1,707 22 60 38 739 26 70 42
89-90 1,482 21 60 36 811 24 70 40
90-91 418 22 60 40 212 35 70 49
91-92 186 22 58 37 69 27 65 43
92-93 123 16 60 37 103 26 70 47
93-94 1,577 14 60 .37 439 25 70 44
94-95 289 23 70 43 118 34 80 63

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