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

RECRUITMENT ANP, SURVIVAL OF YOUNG-OF-THE YEAR (YOY)
BROWN TRO~JT (Salmo trutta L.) IN THE SOUTH FORK OF
THE RIO GRANDE RIVER VERSUS PARENT SPAWNER DENSITY,
' STREAM DISCHARGE AND FRY HABITAT.
R. BARRY NEHRING
COLORADO DIVISION OF WILDLIFE
2300 SOUTH TOWNSEND
MONTROSE, COLORADO 81401
RICHARD ANDERSON
COLORADO DIVISION OF WILDLIFE
2126 N. WEBER
COLORADO SPRINGS, COLORADO 80907
ABSTRACT
Population estimates were conducted on the South Fork of
the Rio Grande River, Colorado, the last week in September 1976-
1983. Marked differences between years were. observed in the number
of YOY brown trout. High levels of recruitment were observed in
1977, 1978, and 1981, compared with poor recruitment in 1976,
1979, and 1980. Recruitment levels were moderate in 1982 and 1983.
YOY recruitment was poorly correlated with parent spawner density
the previous fall (r = +0.2437). Numbers of YOY brown trout in
the population were positively correlated with weighted usable
area (WUA) for fry habitat during the spring run-off period
(r = +0.7734). Numbers of YOY brown trout in the population were
positively correlated with weighted usable area (WUA) for fry
habitat during the spring run-off period (r = +0.7734). Numbers
of YOU brown trout were negatively correlated (r = -0.8854) with
spring discharge levels (mean daily discharge/month for April,
May, June, and July). Relative percent survival of YOY brown trout
(as determined by comparing YOY sampled in the fall with the
potential number of eggs available for deposition the previous
fall) showed strong positive correlation (r = +0.9824) with FIUA
brown fry habitat for April-July over the 8 year period and a
strong negative correlation (r = -0.9785) with mean daily
discharge/month for April through .Tuly. A power curve regression
analysis provided the best fit for tlie. data in all comparisons.
INTRODUCTION
The South Fork of the Rio Grande River, formed by water from melting
snow, flows northeast from the slopes of the San Juan Mountains in the vicin-
ity of 4Jolf Creek Pass and joins t}~e Rio Grande River at South Fork, Col~rado.
The riv~r drains an area of 559 km has an average discharge of 5.891 m /sec
(208 ft /sec), and is relatively unaffecr.Pd by irrigation diversions. The
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