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EXECUTIVE SUMMARY
<br />The purpose of this study was to evaluate the seasonal composition and
<br />density for native and nonnative fishes in two ponds with different bottom shapes
<br />and configurations--one pond was a gravel-pit depression that holds water year-
<br />round (Gardner Pond) and the other was slightly graded toward the mainstem river
<br />but holds water seasonally (Hotspot Pond) -- and both are connected to the mainstem
<br />Colorado River in the same general stream reach. The objective of the study was
<br />to determine which pond configuration and bottom shape might benefit endangered
<br />and other native fishes and reduce or eliminate nonnative fish that are thought
<br />to adversely impact endangered fishes. Prior to the biological evaluation, a
<br />portion of the dike of Gardner Pond, which was a former gravel-pit depression,
<br />was removed and a channel excavated to connect the pond with the river to provide
<br />fish access.
<br />Nineteen adult Colorado squawfish were captured from both Gardner and
<br />Hotspot ponds in 1996. In Gardner Pond, three were captured during pre-runoff,
<br />seven during runoff, and two during post-runoff. In Hotspot Pond, one was
<br />collected during pre-runoff, six during runoff, and none during post-runoff.
<br />During pre-runoff, nonnative sub-adult and adult fish comprised 85% and 97% of
<br />the catch in Gardner and Hotspot ponds, respectively. The most common fishes
<br />collected in Gardner Pond were: black bullhead (36X), white sucker and common
<br />carp (19% each). Species relative abundance was similar for Hotspot Pond: black
<br />bullhead (31X), common carp (26X), and white sucker (18X). During runoff, native
<br />fish comprised 37% and 13% of the catch in Gardner and Hotspot ponds,
<br />respectively. The most common fishes collected in Gardner Pond were flannelmouth
<br />sucker (33X), green sunfish (24X), and white sucker (21X). The most common
<br />fishes collected in Hotspot Pond were white sucker (33X) and black bullhead
<br />(18X). The most common native fish collected in Hotspot Pond during runoff was
<br />flannelmouth sucker (5X). During post-runoff, nonnative fish comprised 99% and
<br />98% of the catch in Gardner and Hotspot ponds, respectively. The most common
<br />nonnative fishes collected from Gardner Pond were black crappie (24X), common
<br />carp (20X), white sucker (20X), and black bullhead (15X). For Hotspot Pond,
<br />black bullhead (28X), white sucker (21X), largemouth bass (19X), and common carp
<br />(18X) were the most commonly caught fishes.
<br />Nine different species of mostly small, young-of-the-year fish as well as
<br />sub-adults and adults of some smaller species such as red shiner, sand shiner,
<br />and western mosquitofish were collected with seines in July to determine annual
<br />reproduction of young-of-the-year fishes. A total of 832 fish representing eight
<br />species were collected in Gardner Pond; 413 fish representing eight species were
<br />collected in Hotspot Pond. Five nonnative fish species (black bullhead,
<br />largemouth bass, black crappie, green sunfish, and western mosquitofish) had
<br />successfully reproduced in both ponds. Numerically, the eight fish species
<br />collected in descending order in Gardner Pond were black crappie (40X), black
<br />bullhead (32X), largemouth bass (17X), western mosquitofish (7X), green sunfish
<br />(3X), common carp, red shiner, and bluegill (each < 1%). In Hotspot Pond, the
<br />eight most common species were largemouth bass (35X), western mosquitofish (30X),
<br />black crappie (22X), green sunfish (8X), black bullhead and sand shiner (each
<br />2%), red shiner (1%), and common carp (< 1%). Densities (fish/lOm2) for the five
<br />most common fishes collected in Gardner Pond were: black crappie (6.2), black
<br />bullhead (5.1), largemouth bass (2.7), western mosquitofish (1.2), and green
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