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

was visually and by touch estimated as silt (< 0.12 mm), sand

(0.12 - 1 mm), gravel (1 - 64 mm), and cobble (> 64 mm). Cover

was recorded as presence or absence of woody debris. With the

exception of cover, the nine measurements were averaged to give

mean depth, velocity, and percent coverage of substrate types for

each habitat.

Habitat availability was measured within each study site to
characterize seasonal and spatial differences. Measurements were
taken along 10 equally spaced transects at the wider sites (3 and
4) and 20 equally spaced transects at the narrower sites (1 and.
2). Depth, velocity, and substrate measurements were made at
equidistant points along each transect to give a total of 100
data points per site.

Data analysis.-To account for ontogenetic shifts in habitat use

we categorized the most common species into three age-groups:

larvae, juvenile, sub-adult/adult (Table 1). Only juveniles of

rare species were considered because numbers of adults and larvae

did not allow for statistical comparisons. The separation

between larvae and juveniles was made at the approximate size at

which a species acquired its full complement of fin rays. The

upper size for juveniles was determined using length-frequency

histograms and was approximately the maximum size the species

attained through the first winter of life. For small-bodied

species (Cyprinella lutrensis, Pi~ephales promelas, and

Rhinichthys osculus), any specimen larger than a juvenile was

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