7729

• UCREFRP Catalog Number: 7729
• Author: Valdez, R. A., W. J. Masslich and A. Wasowicz.
• Title: Annual Summary Report - 1990\
• USFW Year: 1991.
• Copyright Material: NO

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Dissolved Oxvgen

Dissolved oxygen was measured at 10 locations in the Dolores River during Trip 3 and ranged from
6.5 to 8.1 mg/L. EPA's standards for non-salmonid waters fisheries are 6.5 mg/L for early life stages
and 6.0 mg/L for all other life stages.

4.4 Macroinvertebrates

Results of macroinvertebrate sampling in the Dolores River in 1990 are presented in Tables 33-35.
During Trip 1, 86.3% of all macroinvertebrates sampled were Dipterans, mostly from the family
Simullidae. Composition from other orders never exceeded 10% of the total sample. Three orders
dominated the sample composition from Trip 2; Trichoptera, Ephemeroptera, and Diptera at 39%,
30.2% and 22.4% respectively. Dipterans comprised 55.5% of all samples on Trip 3, followed by
Trichoptera (22.3%) and Ephemeroptera (12.7%). The composition of macro invertebrates shifted
gradually downstream through the sample reaches. Most insects sampled in the lower reaches were
of orders Trichoptera (mostly Hydropsychidea), Ephemeroptera and Diptera (mostly Simuliidae),
comprising 40.2%,28.7% and 25.6% of the total, respectively at the lower most sampling site (RM
1.2) and 26.5%,38% and 28.7% respectively at the next lowest sampling site (RM 59.7). Dipterans
dominated samples taken from above this point. Composition of Dipterans as a percentage of the
total samples for collections at RM 64.4-64.6 and RM 122.6 were 56.5% and 70% respectively. Over
90% of all insects collected in the San Miguel sampling station were Dipterans.

Crayfish (Orconectes virilis) were also abundant in the Dolores River. This cructacean is a potential
predator on young fish. Crayfish densities appear to increase in upper portions of the study with very
high localized densities. Beck (1989) reported mean catch rates of 31.8 crayfish/trap day near
Bradfield Bridge and 3.3 crayfish/trap day immediately below Disappointment Creek in 1989.

5.0. PRELIMINARY FINDINGS

1. Colorado squawfish, humpback chub, bonytail and razorback sucker were not encountered in the
Dolores River in 1990. Non-native fish comprised 83.8% of the total catch. Native species comprised
13% of the total catch. Red shiner was the most common fish captured.

2. Channel geomorphology appears to provide physical attributes suitable for spawning, adult juvenile
habitat and limited nursery habitat.

3. Flow may limit use by Colorado squawfish; McPhee has reduced spring flows but may supplement
base flow; reduced spring flows are allowing silt accumulation that may eventually armour the
substrate; lack of flushing flows may allow parasites to proliferate.

4. Water quality is unknown, but increased elements during stochastic events indicates toxic
substances remain trapped in muds and tributaries.

5. Non-native fishes outnumber native fishes and competition and predation is a problem.

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