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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Following the poor results of the Lake Mohave fish, we attached transmitters to five similar sized
razorback suckers and held them at the Bureau of Reclamation fish holding facilities at Boulder
City, NV. The fish ranged in size from 230 to 270 mm. The fish were inspected once a week to
determine transmitter shedding and subsequent post-healing. When the transmitter was
eventually lost, it left a small wound which healed in 2-3 weeks. The average transmitter
retention was 3.8 weeks (2 to >8 weeks) and all experimental fish recovered.

Transmitter retention time for the smaller (TL x = 241 mm) Lake Mohave fish was shorter (<2
weeks) than of our tank fish or the larger Lake Powell fish (> 4 weeks). We believe there might
be atleast two reasons for this. First, we know that reservoir fish concealed themselves in
aquatic macrophytes. We observed one study fish in Lake Mohave trailing a long strand of
pondweed from its transmitter. Snagging undoubtedly could speed the shedding process.
Vegetation was not a factor in the holding tank experiments nor are aquatic macrophytes
common in Lake Powell. The second factor could be the ossification of the fishes dorsal keel.
Younger fish have softer tissues which are less capable of supporting a transmitter. The use of a
single, rather than multiple sutures undoubtedly is less intrusive, but may also be less permanent
than double sutures.

Unfortunately, mortality is common with surgical procedures. Survival of adults reported by
other researchers has also been highly variable (0-100%) with most studies achieving a 50-70%
survival rate (Marsh and Minckley 1989, Creef and Clarkson 1993, Ryden and Pfeiffer 1995,
Karp and Mueller 1996, Burdick and Bonar 1997, Holden et al. 1997, Ryden 1997b). While
external attachment may be inappropriate for long-term studies, it does provide an alternative
for short-term studies. The dorsal keel found on the razorback sucker and some other native
Colorado River fish provides a unique attachment spot. This approach is non-lethal, less
intrusive than abdominal surgery and allows a mechanism for transmitter shedding for all ages of
fish.

Management and Research Implications

Au~mentation and Recovery Efforts

Reservoir habitat will continue to playa role in augmentation and recovery of native Colorado
River fishes. There is growing evidence that razorback suckers migrate between flowing and
non-flowing habitats (Karp and Mueller 1996, Ryden 1997a, Mueller and Wydoski 1995, and
unpublished data). High use of shallow, flooded backwaters by juvenile razorback suckers in
both Mohave and Powell lends credence to the importance ofthese habitats during their early life
stage. This dependency is somewhat disturbing since these habitats are also havens for known
predators. In stable habitats, such as Lake Mohave, territorial predators like largemouth bass and
channel catfish are not subjected to high fluctuation in reservoir elevation, which influences
habitat availability. However, in larger reservoirs as lakes Powell and Mead, annual water
elevation can fluctuate as much as 20 m which can cause inflow habitats to migrate as much as