WSP05023

• File Number: 8220.114.J
• Description: Dolores Participating Project
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 1/10/1992
• Author: Nehring/R. Barry-CDW
• Title: Dolores River Fishery Monitoring Studies - April-October 1991
• Water Supply Pro - Doc Type: Report/Study

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Table 7.

Dolores River trout (~40 cm) biomass (kgfha), 1986-1991.

Species 10/86 10/87 10/88 09/89 10/90 04/91 10/91
IFIM Site - Metaska Campground - River Mile 0.5
Brown 1.0 2.5 0 0.9 5.8 4.6 0
Rainbow 1.3 6.3 5.5 20.2 37.8 17.2 13.9
Cutthroat 3.6 9.2 8.6 7.5 20.0 2.0 3.2
Total trout 5.9 17.9 14.1 28.1 58.6 23.8 17.1
Ferris Canyon Campground - River Mile 6
Brown 0 1.6 8.1 20.6 20.9 14.7 3.1
Rainbow 2.1 1.5 10.8 14.7 16.1 4.2 5.3
Cutthroat 0 6.5 6.0 4.7 2.2 18.9 5.3
Total trout 2.1 9.5 24.8 40.0 39.2 37.2 13.7
Rock Stockpile Area - River Mile 10
Brown 0 3.1 4.3 1.9 0 1.6 1.5
Rainbow 0 1.9 5.1 3.4 2.0 8.4 1.4
Cutthroat 0 1.6 6.9 2.4 0 0 0
Total trout 0 6.5 16.3 7.7 2.0 10.0 2.9

The large trout (~ 40 cm) population density and biomass estimates (Tables 6
and 7) have been (with rare exception) in steep decline through all of 1991
for all three species of trout as well as the total trout estimates. The loss
of these larger trout may be due in part to natural mortality (old age).
However, it is quite probable that the loss of these older, larger trout was
exacerbated by the low flows and elevated water temperatures.

Similarly, density and biomass estimates for the intermediate size (20-40 cm)
component of the trout population in October 1991, were as low or lower than
they were in October 1990 (Tables 4 and 5). Density and biomass estimates for
all three species of trout in this size range increased from April through
October 1991; but total trout population statistics in this size group are
lower in October 1991 than they were in October 1990.

During the May 1991 population estimation procedures, the number of trout
marked, captured, and recaptured were recorded by river mile segment. This
facilitated making population and biomass estimates by individual river
section(s). These estimates are contained in Table lA in the Appendix of the
report. Similarly, single pass population and biomass estimates were
completed on 11 different river segments (400-1100 feet in length) in early
August 1991. This information is presented in Table 2A in the Appendix.