9425 - Laserfiche WebLink

Home Browse Search

1 recaptured adults in the upper Verde River to decline with size from 33.7 mm (200-250 mm TL) to 10.3 (301-350 mm TL). Cold water temperatures resulting from hypolimnetic reservoir releases have been blamed for reduced growth rates of Gila robusta and other rare CRB fish (Vanicek and Kramer 1469, Vanicek et al. 1970, Marsh 1985, Kaeding and Osmundson 1988, Clarkson and Childs 2000, Robinson and Childs 2001). Life-history adaptations are also implicated in observed growth rate differences between ulations. Best en 1985) noted that mainstem Gila River roundtail chub ~pulations PoP g in New Mexico grew faster, matured later, and lived longer than those in tributary streams and suggested that such differences may represent variations in life-history strategies that adapt fish to local conditions. Such adaptations were also documented by Smith (1981) as common in many populations of desert fishes. 'vorous with diet d d' on life stage and food Diet. Roundtail chub are omm ~ m8 availability. After emerging, larvae feed on diatoms and filamentous algae (Neve 1976). Juvenile diet consists predominantly of chironomid larvae and ephemeroptera nymphs (Vanicek and Kramer 1969), but may include algae, tricopterans, and osteacods (Bestgen 1985). Large juvenile and adult roundtail chubs consume aquatic insects, crustaceans, 1 fish, plant matter, snails, ants, beetles, crickets, grasshoppers, and lizards (Koster 1957, McDonald and Dotson 1960, V anicek and Kramer 1969, Schreiber and Hinckley 1981, Tyus and Hinckley 1988, Karp and Tyus 1990b, Rinne 1992). Bestgen (1985) reported an average ratio of gut length to standazd length of 0.99:1 for G. robusta <100 mm TL, suggesting adaptation for a largely carnivorous diet. Plant matter may be consumed for the associated epiphytic organisms (Neve 1976, Bestgen 1985). However, increased consumption of algae has been observed with the onset of summer flooding and associated reductions in invertebrate biomass (Neve 1976, Bruns and Hinckley 1980, Schreiber and Hinckley 1981, Bestgen 1985}, suggesting that plant material may be Purposefully ingested. Final Report September 2002 23