9540

• UCREFRP Catalog Number: 9540
• Author: Christopherson, K., G. J. Birchell and T. Modde.
• Title: Larval Razorback Sucker and Bonytail Survival and Growth in the Presence of Nonnative Fish in the Stipprup Floodplain.
• USFW Year: 2004.
• USFW - Doc Type: Salt Lake City, UT.
• Copyright Material: NO

stocked into the sma1124.28 mZ enclosure. This small enclosure was used as a control to test
larval razorback sucker and bonytail survival without nonnative fish present.
The study design was the same for the bonytail. It included two densities of bonytail
(high and low-density) introduced into enclosures with approximately equal numbers of
nonnative adults (Table 1). On May 8, 2002, approximately 71,500 bonytail larvae were
introduced in the high-density enclosure and 21,2501arvae introduced into the low-density
enclosure. An additional 5,2501arvae were introduced into the smaller control enclosure.
Dexter National Fish Hatchery and Technology Center provided the bonytail larvae, which were
introduced into the same enclosures with razorback sucker and thus experienced similar exposure
to nonnative fish.
Fyke nets (0.32 cm and 0.64 cm mesh) were used for sampling outside enclosures. Only
nets with 0.32 cm mesh were used inside the enclosures. On June 22, preliminary sampling was

conducted to measure the growth of razorback sucker and bonytail. A 50-individual sub-sample
was used. Sampling within enclosures occurred again in the first two weeks of August.
Inside the enclosures, nets were set in a star pattern, alternating between low and high-
density sites for five days. Fish captured inside the enclosures were counted and released into ~
the floodplain outside the enclosures. All nonnative fish captured were removed during
sampling. Population estimates with 95% confidence limits for razorback suckers and nonnative
fish inside the enclosures and nonnative fish outside enclosures, were calculated using depletion ~
techniques. Depletion techniques were used inside the enclosure because the level of sampling
was great enough to capture most of the fish. The number of bonytail in each enclosure was
calculated using the removal estimator [M(bh)] from the computer software CAPTURE. 7
Intensive sampling for population estimation outside the enclosures occurred the last
week of July. This was done to measure the level of escapement from the enclosures. Nets were
set outside the enclosures for four consecutive days. Razorback suckers captured outside the ~
enclosures were marked by removing the right pelvic fin. The main wetland outside the
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