9533

• UCREFRP Catalog Number: 9533
• Author: Muth, R. T. and E. Wick.
• Title: Field Studies on Larval Razorback Sucker in Canyonlands National Park and Glen Canyon National Recreation Area, 1993-1995.
• USFW Year: 1997.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

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Diet of Adult Red Shiner: 1994 (Objective 5)

Background.- The red shiner is widespread and common or abundant throughout the
Colorado River system. It is a predominant species in low-velocity nursery habitats of native
fishes. In a survey of Colorado River basin researchers, red shiner ranked second on a list of
28 nonnative fish species considered to adversely affect native fishes of the Colorado River
basin and southwestern United States. Suspected impacts included predation on larvae of
native fishes, especially Colorado squawfish and razorback sucker, and competitive interactions
with young of native fishes, especially Colorado squawfish and Gila sp. (Hawkins and Nesler
1991). Ruppert et al. (1993) documented predation by adult red shiner on cypriniform larvae
(mostly suckers, some identified as blue head sucker Catostomus discobolus) during early
summer 1991 in ephemeral shoreline embayments near the confluence of the Yampa and
Green rivers, Colorado.

Methods.-A total of 435 adult red shiner (40-80 mm TL) collected with seines from the
middle Colorado and lower Green rivers was selected for diet analyses. Of these, 230 were
from the middle Colorado River (206 from Shafer Canyon and 24 from Lathrop Canyon) and
205 were from the lower Green River (28 from Millard Canyon and 177 from the Bonita Bend
area). In the laboratory, the entire digestive tract was removed from each red shiner, contents
were washed into a petri dish, food items were identified to the lowest practical taxon, and
similar taxa were grouped into food categories. Percent fullness and percent contributed by
each food category to total volume of food were visually estimated for each digestive tract. Diet
measures by sampling location were: (1) mean percentage each food category contributed to
total volume of food in each digestive tract (mean of volume percentages) and (2) percentage
of all digestive tracts in which each food category occurred (percentage of occurrence).

Evaluation of Adult Red Shiner Exclosures: 1995 (Objective 2)

Background.- The ichthyofauna of the upper Colorado River basin is now dominated
by nonnative fishes, which have contributed to the decline of many native fishes. There is a
need for effective methods to control the abundance and distribution of these nonnatives and
reduce their negative effects on native fishes, espeCially endangered species (Lentsch et al.
1996; Tyus and Saunders 1996).

Methods.- The feasibility of using netting to block access of adult red shiner into
portions of larval razorback sucker nursery habitats was evaluated in the lower Green River for
two exclosures established before spring runoff. One exclosure was constructed inside Millard
Canyon and one was constructed in a wash at Bonita Bend. Exclosures were constructed of
0.3-mm mesh plastic-coated fabric attached to rebar driven into the substrate on low terraces;
the bottom edge of the fabric was buried in the substrate. Each exclosure encompassed an
area of about 100 m2. Terraces were dry when exclosures were first established, then were
inundated as river flows increased and habitats flooded. The integrity of each exclosure and
fishes inside and outside each exclosed area were monitored over the sampling season to
determine success in maintaining the exclosures and keeping adult red shiner out while
allowing free movement of fish larvae (particularly suckers).

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