9547 - Laserfiche WebLink

Home Browse Search

By the time the fish have reached subadult size (250 - 400 mm), they become increasingly piscivorous. Gradually, the subadults begin moving upstream, perhaps drawn to better habitat and more suitable food. Over a period of years, these fish move into adult habitat many miles upstream of the nursery area. Because the movement is so gradual, they become widely distributed in the system. Male Colorado pikeminnow mature when they are about 8 years of age, and females mature when they are about 10 years old. ~ Razorback Sucker Most of the following text is based on data obtained from studies of razorback suckers in riverine habitat of the UCRB. Despite the fact that most of the razorback suckers remaining in nature are found in Lake Mohave, AZ-NV, rivers are likely to be the focus of restoration efforts in the UCRB. Consequently, the body of information on life ~ history, behavior, and habitat use in lacustrine habitat will be used only sparingly. In winter, razorback suckers in the Green River occupy slow runs, slackwaters, eddies, and backwaters of the main channel (McAda and Wydoski 1980, Valdez and Masslich 1989). The fish are cold-adapted and remain active in winter; local movements ~ increase with increased discharge and flow fluctuations (Valdez and Masslich 1989). Razorback suckers also have been observed using large backwaters in some locations during early spring (Vllestwater Engineering 1996). Razorback suckers in unrestricted riverine habitat exhibit both local and long-distance ~ movements in spring and summer (Tyus 1987; Tyus and Karp 1990; Modde et al. 1995), although these movements are not as extensive as those observed for the Colorado pikeminnow. During spring migrations, fish may move 50 to 190 km to spawning sites in the Green and Yampa rivers (Tyus and Karp 1990). Radiotracking studies and recaptures of tagged fish on spawning grounds have documented homing ~ to specific spawning sites, to which the fish show fidelity. Similar homing movements are known for other catostomids, where at least 95% of the spawning fish migrate to their home stream (see Dence 1948, Werner 1979). Recent studies have implicated olfactory imprinting as the mechanism by which razorback suckers locate spawning areas. Scholz et al. (1992, 1993) confirmed that a burst of thyroxine occurred during the sac-fry stage, immediately before the larvae swam up from the cobbles and entered ~ downstream drift. Thyroxine activity in other fishes has been associated with a period of sensitivity in which olfactory imprinting can occur (Hasler and Scholz 1983, Scholz et al. 1992, 1993). The RIP has supported two studies of olfactory imprinting in razorback suckers. Fish ~ exposed to two different chemicals during the sac-fry stage were later tested in a maze when they were adults. In the first study, most fish moved and oriented to the correct chemical (Haines et al. 1996). Results were less clear in a subsequent study where fewer fish oriented to either chemical (A. Scholz, personal communication), but behavior may have been confounded by the presence of ripe females. In both studies, 19