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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EXECUTIVE SUMMARY

Little information is available regarding the movements and habitat use of early life stages of
razorback sucker (Xyrauchen texanus). Juveniles are rarely encountered in the wild (Minckley
1983, Minckley et al. 1991, Gutermuth et al. 1994, Modde 1996, Tyus 1997). Dispersal and
habitat use of stocked, juvenile razorbacks was studied in lakes Mohave and Powell during the
summer of 1997. Sonic transmitters (90 day) were externally attached to 55 fish, 27 were
released into Lake Mohave and 28 into Lake Powell. Half of each lot was held three days in
blocked coves to test if site acclimation influenced short-term dispersal rates.

Post stocking dispersal was rapid, widespread, and similar to earlier studies in Lake Mohave
(Mueller et al. 1998). Movement was more pronounced immediately after release and declined
with time. Maximum daily distance traveled by individuals released in Lake Powell averaged
>2 krn/d (0->7 krn/d) and daily movements averaged 347 mid (3-1,500 mid) for Lake Mohave
fish and 480 mid (3-1,800 mid) for Lake Powell. After the first week fish were typically found
backwaters and coves and >50% of the fish detected were found in cover. Prevalent cover types
in Lake Mohave and Powell included flooded tamarisk (48-86%), emergent vegetation
(Potamogeton & Najas spp.) (40/0% absent in Lake Powell), and rock cavities (12-14%).

Preliminary data suggests behavioral acclimation may influence short-term dispersal rates. Of
the 14 Lake Powell fish that remained in the study area for> 30 days, twice as many (64%)
represented fish held for 3 day than those simply released. The sample size was small and might
simply reflect normal variability, however, it's doubtful holding fish deter fish from remaining in
the general area and might encourage it. To few contacts were made in Lake Mohave to draw
any conclusions.

Sonic transmitters have been used successfully for tracking other fish species (Pelle and Paulson
1993, Marsh 1997, Mueller et al. 1998), however, they proved less effective on juvenile suckers
that typically were found using shallow, vegetative backwaters. These habitats greatly reduced
the effectiveness of sonic equipment. On the basis of our studies, we recommend that stocking
programs consider the following:

* Expand monitoring programs to sample shallow, flooded habitats (i.e., <2 m depths).
* Stock only fish larger than 30 cm in length.
* Investigate seasonal (autumn-winter) rather than year-round stocking.
*Examine reservoir fluctuation zones and how changes in reservoir elevation influences
predator population dynamics (i.e. densities, colonization rates).
* Use radio, rather than sonic transmitters for future juvenile telemetry studies.

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