7080

• UCREFRP Catalog Number: 7080
• Author: Carter, J. G., V. A. Lamarra and R. J. Ryel
• Title: Drift of Larval Fishes in the Upper Colorado River
• USFW Year: 1986
• USFW - Doc Type: Journal of Freshwater Ecology
• Copyright Material: YES

We conducted two independent studies of larval fish drift in the upper
Colorado River. A 1983 study was designed to assess the potential impact of
a midchannel water intake structure near Parachute Creek, Colorado (Figure
1). A 1984 study assessed the potential imput of a small shorel ine
hydropower project near Plateau Creek, Colorado (the Palisade Site).

METHODS

Both studies were conducted from mid-June to early September. Five
gear types were used at each study site, including large-mesh seines to
document adult and juvenile species composition; small-mesh seines, dip nets
and light traps to assess the composition of non-drifting larvae and young-
of-the-year along shorelines and in shallow areas; and drift nets to assess
species composition and relative densities of drifting larvae. Tow nets
were also used at the Parachute Site to assess midchannel surface drift, and
boat electrofishing was used at the Palisade Site to further document adult
and juvenile species composition.

The drift nets were 560 micron mesh Nitex plankton netting with a
rectangular opening of 30.48 x 45.72 cm and a length of 3 m, which tapered
to a removable collection cup. Each net was set with the open end facing
directly into the current and even with the surface of the water, except for
pa ired, stacked sets used to assess vertical distribution. Time, water
temperature, and velocity were recorded when each drift net was set and
removed. The tota 1 volume of wa ter fil tered by eac h net was computed us i ng
the average of the initial and final water velocities at the net opening.

Dri ft samples were preserved with 10'; formal in; fish were sorted from
the debris as soon as possible and transferred to 5% formal in. Each larval
fish was examined microscopically to identify the specimen, measure its
total length, and determine its stage of development. Identification of
specimens was based on criteria presented by Snyder (1981).

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fIGURE 1. locations of Parachute and Palisades study sites.

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