8061

• UCREFRP Catalog Number: 8061
• Author: Mueller, G. and P. Marsh.
• Title: Post-Stocking Dispersal, Habitat Use, and Behavioral Acclimation of Juvenile Razorback Suckers ‎(
• USFW Year: 1998.
• Copyright Material: NO

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Behavioral acclimation may also be a factor. Of the 14 Lake Powell fish that remained in the
study area for more than one month, we encountered twice as many cove held fish (64%) as
those simply released and not held for 3 days (Figure 6). The sample size was small and might
simply reflect normal variability, however, it appears that holding does not deter fish from
remaining in the general area and might encourage it. The data collected from Lake Mohave
were inadequate to draw any conclusions.

Habitat Use

Juvenile or subadult razorback suckers were found using the same broad, shallow, shoreline
habitats as adults. They were seldom found in narrow, deep, canyon habitat. While adults are
generally found in open areas along the shoreline (Mueller et al. 1998), juveniles are more
secretive, being found in the back of coves or flooded washes hidden in vegetative or rocky
cover. Fish were typically found within 10m of shore and depths were less than 2 m.

Our findings support earlier observations in rearing ponds that young suckers were nocturnal and
effectively concealed themselves in submergent vegetation during the daytime (Mueller and
Marsh 1993). These shallower habitats naturally provide warmer temperatures and more food
production; important factors in rapid growth. Surface water temperatures ranged 1-3 degrees C
higher in these backwaters than the main lake. This mimics earlier information we collected in
Lake Mohave (Mueller et al.1998). Body temperature data collected for 10 adults and one
juvenile suggests the two-year old fish normally inhabited a thermal regime equal to, or greater,
than the maximum temperature range used by adults (Figure 7).

Juveniles had a strong preference for flooded backwater complexes at Castle Creek Canyon and
Mike's Canyon. These two sites afforded fish the largest, shallow, flooded habitats in the San
Juan Arm, next to Piute Farms when lake elevations exceed 1,120 m (3,680 ft). These areas are
similar to areas where juvenile razorbacks have been found in the Green River at Old Charley
Wash (Modde 1996 and 1997). Dispersal appears to be strongly influenced by habitat/cover
availability. The rapid dispersal observed in riverine systems suggests that habitat conditions
did not attract and hold young fish. The physical changes brought about by channelization, loss
of backwaters and oxbows, fluctuating hydroelectric releases, and the decline of large snags and
other woody debris, have undoubtedly effected cover availability.

External Attachment Technique

Attachment of transmitters to the dorsal keel worked well as a short-term approach and is
possibly the only practical method of studying the movements of juvenile suckers. We observed
no initial mortality and all 55 fish left the release sites. We feel attaching transmitters to the
dorsal keel is less intrusive than the common dart tag which is generally inserted into the dorsal
musculature and is less stressful than surgery for short-term, behavioral studies.

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