Laserfiche WebLink
apparent hybridization between humpback and bonytail chubs has resulted in <br />the term "complex" being applied to intergrades between the two species (Holden <br />and Stalnaker, 1970). Specimens of the humpback chub complex have been collected <br />in Echo Park on the Green River (McAda and Seethaler, 1975) and in Desolation <br />Canyon (Holden and Stalnaker, 1975a). The bonytail chub was considered abundant <br />in the Green River in Dinosaur National Monument in the mid 60's (Vanicek and <br />Kramer 1969). However, in the mid 70's, none were collected at the Monument <br />in two summers of sampling (McAda and Seethaler, 1975). Individuals have been <br />found in the Green River in Desolation Canyon and in Canyonlands National Park <br />(Holden and Stalanker, 1975a). <br />A fish collected 1 mi (1.6 km) up from the mouth of the White River was <br />identified in the field as an adult of the commonly found roundtail chub (G. robusta). <br />Bright red spawning colors were apparent on the underside of this 345 mm-long <br />fish. After later examination of several photographs, it was decided that <br />the fish was probably not a roundtail, but was either a bonytail chub or, more <br />likely, a member of the humpback chub complex (P. Holden, BioWest, Inc., <br />personal communication). <br />Other Endemic Fish Species <br />Roundtail Chub (Gila robusta) <br />The roundtail chub, commonly known as the Colorado chub, is native to the <br />Colorado River Basin. It has decreased in abundance as the Colorado continues <br />to be modified by man (Miller, 1961). The young of this species and of the <br />Colorado squawfish are similar except for a prominent black spot on the caudal <br />peduncle of the squawfish juvenile. Adults of the two species can be easily <br />distinguished. During spawning in late spring, breeding males are reddish <br />on the sides of the head and body, below the lateral line. Normal size of <br />the roundtail adult is 8 in (21 cm) to 13 in (34 cm). In this study, lengths <br />were measured and within season growth of age groups zero to two was readily <br />evident (Figure 2). A weight-length relationship (r2=0.76) was also found <br />using data from 118 fish and was as follows: Length (in millimeters) = 2.5 <br />Weight (in grams) + 79.5. The appearance of recently hatched fry during mid- <br />August (Figure 2) is somewhat later than that reported for the roundtail population <br />in the Green River (Vanicek and Kramer, 1969); however, general growth patterns <br />for each age group were similar. An analysis of representative scale samples <br />from fish of the first three age groups showed that age group 0 and I were <br />scaleless; age group II had scales but no annuli. This finding agrees with <br />that of Vanicek and Kramer (1969). The absence of larger fish in the White <br />River collection may have been due to gear selection and/or the difficulty in