7404 - Laserfiche WebLink

Home Browse Search

' INTRODUCTION This Interim Report presents preliminary data from field work conducted to evaluate the spawning ' success of the 1990 year class of Colorado squawfish (UDWR Contract No. 90-2558). Field work was conducted on the lower Green River (RMI 120 to RMI 0) during September 17-20, 1990. Information in this report will generally be presented in a tabular format to provide a synopsis of trip ' details and preliminary data analysis. The results of this trip will be integrated into the regular post- larval, age-0 Colorado squawfish monitoring program of the ISMP (Interagency Standardized Monitoring Program, USFWS 1987) and presented in an Annual Report in January 1991. BACKGROUND ' Recent investigations in the lower 50 miles of the Green and Colorado Rivers, above their confluence, have revealed a large reduction in densities of YOY Colorado squawfish between fall and the following spring and summer (Valdez 1985, 1987, 1988, Valdez and Masslich 1990; Personal communications with Miles Moretti, UDWR, February 1988). This apparent decrease in numbers indicates that these young fish: (1) experience a substantial overwinter mortality, (2) occupy habitats ' in spring and summer unaffected by sampling gear, or (3) emigrate to other regions of the river. To test these hypotheses, age-0 Colorado squawfish were sampled in the spring and fall of each year ' using the same ISMP methodology in order to assess changes in density for the 1987-1990 year classes. Sampling was conducted jointly with Reclamation and UDWR in fall 1987 (September 23-24) and spring 1988 (March 21-25) to examine the 1987 year class; in the fall 1988 (September 26-30) and spring 1989 (March 20-24) to examine the 1988 year class; and in the fall 1989 (September 25-29) ' and spring 1990 (March 20-25). The sampling effort in spring 1990 was conducted jointly with the UDWR on the Green River and with the UDWR and USFWS on the lower Colorado River. Sampling during fall 1990 was conducted jointly with UDWR. Sampling during fall 1990 was conducted on Reach 3 on the Lower Green River (RMI 120 to RMI 0). This report presents results from the fall trip, along with comparisons of results far the previous. three years of sampling. Data are presented for all reaches except Reach 1 on the Colorado River, where sampling was conducted only on the lower 50 miles. Complete analyses of the overwinter survival data for Colorado River Reach 1, including catch rates of sympatric species and catch rates and numbers of Colorado squawfish are being conducted by the USFWS, Grand Junction CRFP Field Station. ' The Methodology employed is consistent with that described in the ISMP. Basically, two backwaters were sampled every 5 miles. Two seine hauls were taken at each backwater and the fish in each counted and all endangered fish measured and released. Depths and dimensions of each backwater and seine haul were also taken. CPUE was computed for each seine haul and averaged with standard deviation far primary and secondary backwaters. This is in contrast to data presented for the spring overwinter survival monitoring which pools data from primary secondary backwaters into one CPUE ' statistic. For purposes of comparison of fall ISMP data to spring OWS data, primary and secondary backwaters are combined for the fall ISMP data. The fall sampling was conducted in late September to maximize the catch of YOY large enough to identify in the field at a time when we believe most ' of the fish occupied- the relatively warmer backwaters. Spring sampling was in late March and early April when water temperatures were warming and prior to the onset of spring runoff which inundated