9319 ‎(2)‎

• UCREFRP Catalog Number: 9319
• Author: Mueller, G., M. Horn, Q. Bradwisch and L. Boobar.
• Title: Examination of Native Recruitment and Description of the Fish Communities Found in the San Jan and Colorado River Interface Zones of Lake Powell, Utah.
• USFW Year: 2001.
• USFW - Doc Type: 01-159,
• Copyright Material: NO

I
I
I
I,
I
I
I
I
I
I
I
,
I
I
I
'I
I
I
I

Light Traps. Quatrefoil style light traps were used to collect larval fishes (Mueller et al. 1993).
Entrance widths were originally 10 mm to facilitate capturing larger native juveniles, however,
potential predators such as adult red shiners and small sunfish also entered. Less than 30 larvae
were captured during the 1999 season. The entrances were reduced to 5 mm to exclude predators
during the 2000 field season. The traps had self-draining plankton nets to concentrate the
samples and three 300-mA light bulbs (total 0.9 A) with two "D" cell batteries that provided
light for 1 0 hours. Lights were placed in a clear 3-cm plexiglass cylinder. Two traps were set
before dark along shore or in the backs of coves and recovered early in the morning. CPUE was
expressed in numbers of larvae per night set (larvae/set).

Seining. Shoreline and backwater habitats were seined at the inflow sites using a nylon 4-mm
meshed 1.5-m by 12-m seine. The seine was pulled going downstream (if current was present)
and the area sampled (m2) was estimated. CPUE was expressed as the number of fish seined per
10 square meters (fish/l 0 m2).

Acoustics. Pelagic fish densities were measured using a scientific echo sounder (BioSonics
Model DT-5000). The system operated at 420 KHz and multiplexed between single and dual-
beam transducers that were mounted on an aluminum platform on the side the boat. Permanent
acoustical transect stations were established at RM 36, 38,40,42,44,46,48,50, and 52 on the
San Juan arm. Addition transect data were collected at Spencer's Camp, Nokai Canyon, Castle
Creek Canyon, and Mike's Canyon. Transects started at shore and proceeded to the thalweg. A
minimum effort of 1,000 pings (approximately 5 minutes of mobile scanning) was collected at
each site. Analyzed data provided size distribution and standing crop information (fish/m3 and
kg/m3).

Sampling Effort

During the 4 sampling days per field trip, a crew of five to eight biologists set a minimum of two
minnow traps, two small-mesh (6 mm) hoop nets, two large-mesh (2.5 cm) hoop nets, two large
(3.7-cm) trammels, and two small-mesh (12 mm) trammels per night at the San Juan inflow and
Spencer's Camp sites. Similar effort occurred at the Colorado River inflow, however, the
number and types of nets used depended upon netting conditions and set opportunities. We
seined (10 pulls) once each inflow trip and set light traps (May-July). All areas were
electrofished using standardized methods developed by the UDWR. Each site was sampled one
night and the effort consisted of three, IS-minute shocking periods. Occasionally sampling was
interrupted due to bad weather, equipment breakdown, or when we experienced high catch rates
(> 1 00 fish/set) for spawning carp and threadfin shad. All fish were released unharmed except
for a total of 40 fish used for a heavy metal analysis (Jerry Miller, BaR). Field trips typically
consisted of 4 sampling days.

Acoustical surveys were conducted before (May) and after the spawning peak (June-August).
All surveys were conducted during daylight hours and took approximately 4 to 6 hours to

7