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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Unfortunately, in Lake Powell, ambient noise generated by a water fall and then by high spring
flows prevented us from effectively monitoring upstream sections of the study area. However,
reservoir survey conditions were generally ideal. Efforts to locate fish downstream of the release
site extended over 72 km. Only two fish moved 2.7 km downstream, the furthest 2.7 km.
Twenty-one of23 fish (92%) moved uplake whereas 84% moved down lake in Lake Mohave. It
is unknown whether this might be a behavioral response triggered by handling, current, turbidity,
or simply a factor of shoreline morphology.

Stockinfl Acclimation Methods of handling and stocking endangered or threatened fishes are
generally the same as for trout, bass, catfish, or other game fish (USFWS 1992, 1994). They are
transported by truck to the release site where they are acclimated to physical conditions,
normally temperature and rarely pH (Stickney 1983, Wedemeyer et a1. 1990). At that point they
are simply released. The Upper Colorado River Basin Recovery Implementation Program (RIP)
has establish stocking criteria and guidelines (USFWS 1992, USFWS 1994), however,
behavioral acclimation is not included. Protocols have been established which mandate that
stocked fish be "released in quiet-water areas (e.g., backwaters) that communicate with the
river." Unfortunately, augmentation programs have met with mixed, if not poor results.

For instance, a ten-year reintroduction program in Arizona stocked nearly 12 million razorback
suckers with no measurable results. The majority were stocked as fingerlings or fry and
subsequent studies showed young fish moved ~ ~ downstream and were rapidly eaten by
channel and flathead catfish (Brooks 1985, Marsh and Brooks 1989, Minckley et a1. 1991).

Since then, some success has been reported by stocking larger fish to reduce predation (Mueller
1995, Marsh 1997, Ryden 1997a). While survival can be improved with larger fish, managers
often have been unable to stock and retain fish in desired locations. Often stocked fish travel
great distances downstream. Several scientists speculated that fish reared in hatchery or rearing
ponds might not have developed adequate muscle tone to cope with flowing habitats (Todd
Crowl personal communique). Laboratory investigations that were conducted proved
inconclusive.

Research on Lake Mohave (Mueller et al. 1998) suggests stocked juveniles travel substantial
distances, even in lentic environments where hydraulics were not a factor. We believe this
supports the contention that other factors, such as normal early life migratory behavior, handling
and transport associated stress, or even habitat conditioning could also be factors.

Recent studies examining the movements and habitat use of bonytail in Lake Mohave found
quite a difference in response between pond-reared and resident fish (Marsh et al. 1996, Foster
et ale 1997). Researchers found that pond-reared bonytails roamed more widely and were more
difficult to detect than resident fish that had distinct territorial ranges. When non-resident
bonytail were found, they were detected in shallow, vegetated habitats, similar to habitats where
they were taken from. Fish captured from the reservoir were more pelagic in nature and were
quite territorial suggesting habitat conditioning might have occurred.

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