7780

• UCREFRP Catalog Number: 7780
• Author: Brooks, J. E., et al.
• Title: San Juan River Seven Year Research Program Summary Report 1992.
• USFW Year: 1992.
• USFW - Doc Type: \
• Copyright Material: NO

In 1993, secondary channels will be inventoried during spring
runoff, summer lowflow, and early autumn. Sites on two or three
secondary channels will be intensively sampled about every three
weeks from cessation of spring runoff through November.
Nonnative Fishes - Investigations of the role of nonnative fish
species in the distribution and abundance of native species in the
San Juan River were initiated during 1991 and continued in 1992.
Sampling was conducted by raft-mounted electrofishing to determine
the overall distribution and abundance of nonnative species between
Hogback Diversion, upstream of Shiprock, NM, downstream to Mexican
Hat, UT. The most common nonnative species collected by
electrofishing, channel catfish and common carp, were tagged during
1992 sampling to determine movement patterns in relation to season
and river flow. Sampling was also conducted to determine food
habits of potentially predatory nonnative species collected by
electrofishing.
Nonnative species were less abundant than native species during
1991 and 1992 mainstream sampling efforts. The relative abundance
of nonnative species collected during 1992 was lower than observed
in 1991. Channel catfish catch rates did not change significantly
during the sampling period. Catch rates for common carp, on the
other hand, declined during 1992 collections and were significantly
less than observed in 1991. Concurrently, catch rates for all
species combined did not change significantly.
Movements of channel catfish and common carp tagged and recaptured
during 1992 sampling efforts were evaluated. Demonstrated movement
patterns for channel catfish and common carp from recapture data
were not remarkable, with a few exceptions. A single channel
catfish captured in October moved upstream 30 RM's after tagging in
June. The only significant movement noted for common carp was of
an adult tagged in June and recaptured 38 RM's upstream in October.
Most fish were recaptured within 2 river miles of the original
capture site.
Analysis of the food items found in nonnative predator stomachs
demonstrated a high frequency of occurrence of macroinvertebrates.
Stomachs analyzed were primarily from channel catfish. Smaller
numbers of nonnative centrarchid species were the second most
abundant predator group sampled. Low numbers of brown trout and
black bullhead (Ameiurus melas) were included in analyses. Fish
and/or fish remains were noted for both groups and identifiable
prey fish found in stomachs were native flannelmouth sucker and
nonnative red shiner. Russian olive fruits were commonly found in
nearly all predator stomachs from all seasons sampled.
Activities to be conducted during 1993 include continuation of
mainstream collections to determine distribution, abundance,
movement patterns, and food habits of nonnative fishes.
Macroinvertebrate sampling will be conducted in low velocity
18