8096

• UCREFRP Catalog Number: 8096
• Author: American Fisheries Society.
• Title: Proceedings of the 19th Annual Meeting, Colorado - Wyoming Chapter, American Fisheries Society.
• USFW Year: 1984.
• USFW - Doc Type: March 7-8, 1984.
• Copyright Material: NO

is severely limited during the spring run-off periods in years of median flow
or higher than median flow. Conversely in a one-in-five low flow year fry and
juvenile brown trout habitat was much higher during the spring run-off period
(April-July). Many studies have indicated a strong relationship between
stream flows or water levels in lakes and levels of recruitment of young fish
(McKernan et al. 1950; Bulkey-and Benson 1962; Brett 1951; Johnson 1956;
Vernon 1958; Wickett 1958; Drummond 1966; Gagmark and Bakkala 1960). Ottaway
and Clarke (1981) found that brown trout fry (post-swim-up) pass through a
stage. when they are very vulnerable to downstream displacement by elevated
stream velocities.
Cursory examination of the number of YOY brown trout sampled each year
versus the mean discharge/month for June (month of peak spring discharge)
indicates a strong inverse relationship might exist (Table 1). Linear
regression analysis of the data in Table 1 gives a correlation coefficient
(r) of -0.8830.
Table 1. Young-of-the year brown trout collected during electroshocking
operations from the South Fork of the Rio Grande River (September
1976-1983) versus mean discharge (June 1976-1983).
Year No. YOY Sampled Mean Discharge (ft /sec)
1976 14
1977 258.
857
113
1978 139 696
1979 10 1746
1980 19 1441
1981 270
1982 84
1983- 59
319
856
A mark and recapture analysis of YOY brown trout in 1977 indicated we
were recapturing about 6.6 percent of the marked fingerlings on the second
shock. Electroshocking conditions such as water flow, crew size and shocking
efficiency were quite constant between years. Thus, we used the 1977 shock-
ing efficiency to get an estimate of the number of YOY brown trout in the 3
study areas each fall. Then, by dividing the fall population estimate for YQY
brown trout by the number of eggs available for deposition the previous fall
(as described in the Methods and Materials Section) we derive a figure we
designate "relative percent survival". This in essence corrects the YOY
population estimate for any impact of parent spawner density. This figure
(relative percent survival) was regressed against WUA brown fry habitat and
mean discharge/month for April, May, June, and July (spring run-off period)
1977-1982. The .data used in these regression analyses (using a-power curve
regression) are presented in-Table 2.
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