9688

• UCREFRP Catalog Number: 9688
• Author: Upper Colorado River Endangered Fish Recovery Program.
• Title: Nonnative Fish Control Workshop Summary, Conclusions, and Recommendations.
• USFW Year: 2002.
• USFW - Doc Type: Lakewood, CO.
• Copyright Material: NO

Table 4. Fish captured and recaptured from sampling in Mack Wash downstream of Highline
Lake Dam.
1999 2000 2001 Total/Mean
All Fish 1,315 1,566 1,393 4,247
Percent Native 11 % 44% 35% 30%
Percent Nonnative 89% 56% 65% 70%
Number and Percent LMB 247 (19%) 128 (8%) 19 (1%) 376 (9%)
Number and Percent Marked
Fish After Net's Installation 4 of 714
(0.5%) 8 of 1,566
(0.5%) 4 of 1,393
(0.3%) 16 of 3,673
(0.4%)
Species Recaptured
Total Lengths 1 YLP, 3-LMB
120-130 mm 1 GSF, 7 LMB
80-130 mm 3 GSF, 1 LMB
108 mm 4 GSF, 10 LMB,
1 YLP
120; Figure 8), the number captured below the dam in 1999 (230) was about half that in 2000
(127) and even lower in 2001 (19) (Figure 9). The low number of marked fish captured below
the dam and the declining numbers of most sport fish species captured each year suggests the net
was highly effective in controlling fish escapement from the reservoir when properly maintained
(Figure 9).
The net also improved fishing at Highline Lake. Stocked largemouth bass and bluegill stayed in
the reservoir and did not escape into Salt Wash and the Colorado River. The net was left in place
over winter to maintain containment year-around.
Limnological sampling identified an opportunity to reschedule annual maintenance releases from
the reservoir's unscreened bottom outlet from early spring to mid-summer when low dissolved
oxygen levels precludes or minimizes fish presence in this zone and therefore, escapement from
the reservoir. In 2001, the maintenance release was performed in September instead of March.
Sampling showed that dissolved oxygen levels had begun to rebound, but cursory sonar
observations indicated fish did not occupy the deep water near the outlet. This aspect of the
study showed that timing bottom maintenance releases with oxygen depletion in the reservoir can
minimize the need for a bottom release screen. In case of emer~encv or extended bottom
releases, it maybe necessary to fabricate a bottom release screen "sock" to control fish
escapement.
A sample of the net from nearshore, exposed to maximum abrasion and ultra-violet light, was
submitted to the net's manufacturer for an evaluation of its remaining strength. The break test
revealed a 33% strength loss over the net's 2.5-year service life in the section exposed to
maximum abrasion. It is believed that the body of the net has also experienced some strength
loss, and it appears appropriate to begin budgeting for the net's impending replacement.
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