8173

• UCREFRP Catalog Number: 8173
• Author: Gido, K. B. and D. L. Propst.
• Title: Habitat Use and Association of Native and Nonnative Fish in the San Juan River, New Mexico and Utah.
• USFW Year: n.d.
• USFW - Doc Type: \
• Copyright Material: NO

Data collection.-We began sampling study sites 1 through 3 in

mid-July 1993 and site 4 in August 1993. Each site was sampled

at three week intervals from peak spring runoff (late June -

early July) through November and then every sixth week until the

next year's spring runoff. Our study lasted for almost two

years, ending in May 1995.

The high turbidity of the San Juan River precluded direct

observations of fish. As an alternative, we sampled fish by

seining or electrofishing habitats. Habitats were chosen to

represent homogeneous areas that we considered distinct (e.g.,

pools, riffles, and eddies), based on seven years of previous

sampling in the San Juan River. The majority of the habitats

were sampled using a 1.6 mm mesh drag seine (2.5. m x 1.2 m). In

habitats where seining was inefficient (shallow, large substrata)

we used a Smith-Root (Type VII) pulsed DC backpack electrofisher

in concert with the seine. Mean width and length were taken for

each sampled habitat to estimate fish density (number of

individuals m-2). Fish >100 mm TL were identified in the field

and released; the remainder were preserved in 10% formalin and

returned to the laboratory where they were identified and

counted. All retained specimens were accessioned to the New

Mexico Department of Game and Fish Collection of Fishes.

Depth, water velocity, substrate, and cover were determined

at three points along three evenly-spaced transects in each

sampled habitat. Velocity was estimated with a Marsh-McBirny

Model 2000 digital flow meter at 60% depth. Dominant substrate

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