7048 - Laserfiche WebLink

Home Browse Search

another, but no instances of sustained swimming in these areas of higher velocity were ever observed. The numerous pockets and eddies created by the vegetation beds probably allow the chubs to survive in what would otherwise be an unsuitable environment. The tui chub, as a' species, is primarily a low velocity, lake adapted fish. Moyle (1976) states that "Tui chubs ...[are] most commonly... found in the weedy shallows of quiet waters of sluggish rivers". Kimsey (1954) observed the tui chubs in Eagle Lake to be primarily lacustrine in habit. The relatively poor swimming performance of the Mohave tui chub in high velocity water was a major factor in its displacement from its native range by the introduced arroyo chub, Gila orcutti (Castleberry 1985). The wide head, chunky body, and moderately sized fins of the Owens tui chub suggest a morphology adapted to slow-moving waters, which is typical of fishes inhabiting dense cover habitats of lakes, ponds, and riverine backwaters (Lagler et al. 1977). Predator Avoidance. Stomach contents of 109 trout taken from the CD headspring on four seasonal samplings were examined to determine if predation on chubs was significant. Not one instance of predation on chubs or eggs was found, which indicates that chubs are not a preferred food item. . This might also be due to the species and size of trout present in the headsprings. The population of trout is almost entirely domestic rainbow trout which have escaped from nearby raceways. The mean fork length in the four samples was 265, 221, 209, and 195 mm, and, based on observations while electrofishing, these sizes are representative of the trout in both headsprings. According to some studies, rainbow trout do not become piscivorous until they reach a size of 300 to 350 mm (McAfee 1966). Their potential as a predator probably influences chub behavior however, and predation probably occurs to some degree, given the piscivorous nature of trout. Trout are not the only predators on the chubs. Flocks of black crowned night herons, Nycticorax nycticorax, and great blue herons, Ardea herodias, are common in the vicinity of the hatchery and have been observed in the headsprings on several occasions. In addition, many of the chubs captured in the traps and by electrofishing had large scars across their dorsal and lateral surfaces, which were probably caused by herons. Feeding Behavior. The results of the gut content analysis indicate that Owens tui chub are generalist feeders that utilize a wide variety of food items. Twelve different food categories were identified (five categories of aquatic invertebrates were combined into one to facilitate graphing) (Fig. 6). Some items,. such as detritus and plant material, are underrepresented however, because the percent number values were arbitrarily assigned a value of zero. 20