1108 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I FINDIRiS The following findings are submitted at this time relative to the stated objectives: Objective 1: Determine spawning locations of endangered fishes in Cataract. 1. Investigations in 1985, 1986, and 1987 in Cataract Canyon have failed to locate specific spawning sites of Colorado squawfish and humpback chub. 2. High densities of larvae and YOY squawfish in the lower 50 miles of the Green River, immediately above Cataract Canyon, indicates that significant reproduction occurs in this area, but it appears that only low numbers of these fish are being transported by river currents into Cataract Canyon and into upper Lake Powell. 3. Low densities of larval Colorado squawfish in Cataract Canyon indicate that some spawning may occur in the canyon and immediately downstream in the inflow to Lake Powell. 4. The origin of larval and YOY squawfish found wi thin Cataract Canyon is unknown, but the large variation in hatching dates back-calculated from fish length, indicates that many of these fish are being transported by river currents from more than one spawning site and spawning event upstream. 5. Back-calculated hatching dates of squawfish captured in the Cataract Canyon region indicate that peak spawning times for 1985, 1986, and 1987 have varied annually by as much as one month. 6. Colorado squawfish that are hatched relatively late in the year (e.g. August) are smaller in the fall than those hatched relatively early (e.g. July). This leads to a hypothesis that overwinter survival is higher in early-spawned year classes because these fish are larger and more able to cope with winter riverine conditions when backwaters become too cold or ice laden to accommodate the young fish. Objective 2: Determine whether humpback chub populations exist in Cataract. 1. The presence of larval and YOY humpback chub in Cataract Canyon in 1985, 1986, and 1987 is strong evidence that a reproducing population of this species exists in the canyon. 2. Fish that are considered to compose the adult population of humpback chubs in Cataract Canyon are a small morph (generally <200 mm TL) with less than pronounced features considered typical of the species. It is hypothesized that the form in Cataract Canyon is the G. cypha genotype, but may differ phenotypically from other populations. 25