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

3.4 Reservoir Escapement Prevention Measures
3.4.1 Highline Screening Operation and Management (Project No. CAP-20; CDOW)
Escape of nonnative fish from Highline Lake into critical habitat of the endangered Colorado
pikeminnow, razorback sucker, humpback chub, and boriytail in the Colorado River has been an
ongoing concern. Highline Lake is located about 15 miles northwest of Grand Junction,
Colorado; the lake drains into Mack Wash and then into Salt Creek into the Colorado River,
about 6 stream miles from the lake. In the year 1999, a program was initiated by the Colorado
Division of Wildlife, through the Upper Colorado River Endangered Fish Recovery Program
(UCRRP) to screen the outlet from Highline Lake and minimize escapement of nonnative fishes.
The screen installed at Highline Lake was a 363-foot wide x 19-foot deep x 0.25-inch aperture
spillway barrier net fabricated of Dyneema (dry weight = 1,400 pounds). The screen was
installed in Highline Lake in August 1999 to control escapement of juvenile and adult nonnative
fish. Highline Lake covers-160 surface acres, has a maximum depth of 50 feet, and is at 4700
feet elevation. The UCRRP provided $384,000 in funding, including costs for the net ($95,000);
evaluating net options, feasibility analyses, and engineering ($87,000); coordination and
administration ($42,000); and installation ($160,000) (Table 3). Evaluation of the net's
performance and effectiveness in controlling fish escapement in 1999-2001 was $65,000. The
estimated serviceable net life was projected to be 3-5 years under local climatic conditions.
Monitoring of the net's performance included observations on:
• the seal between the net's bottom skirt and the lake bottom;
sand and gravel being wave-washed onto the net nearshore; and
the net's main float line submerging during a period of high flow through the
reservoir.
Aspects of the net's maintenance included:
• estimated vs. actual expenditures for inspections and cleaning in 2000 and 2001;
leaving the net in place over winter vs. removing it; and
correcting the tendency for the net's top skirt to sag and adjoin the net's main
float line.
Initially, annual maintenance costs for the net were projected to be about $15,000. Actual costs
to maintain the net totaled $12,OOO.in 2000 and $5,650 in 2001. The lower cost in 2001 was
because the net was cleaned by personnel from Colorado Division of Parks and Outdoor
Recreation (State Parks administers recreational activities on Highline Lake) instead of by hired
divers.
The net is fabricated of Dyneema and is claimed to last longer than nylon. Dyneema has the
highest specific strength and modulus among commercial organic fibers. The specific gravity of
Dyneema, 0.97, is the lowest among super fibers and is lighter than water. Medium to heavy
growth of medium moss accumulated on the net during operation in 2000, resulting in "heavy
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