8233 - Laserfiche WebLink

Home Browse Search

similaz size as those collected in the lower Green River (Muth et al. 1998). After considering all available larval razorback sucker data sets collected throughout the Green River system (results of this study included) Muth et al. (1998) concluded: "Eazlier first occurrence of razorback sucker lazvae in collections from the San Rafael confluence or lower Labyrinth-upper Stillwater Canyon reaches compazed to collections from the middle Green River suggest that at least some reproduction occurred in the lower Green River each yeaz during 1994-1996." A razorback sucker population or contingent of a lazger population likely persists in the lower Green River as evidenced by the sporadic collection of adults but more importantly through the collection of larvae. It is likely that razorback suckers aze spawning in the Green River in the vicinity of the San Rafael River or possibly in the San Rafael River itself. Due to these collections, the current basin-wide monitoring program for razorback sucker has increased sampling efforts in the lower Green River. This monitoring program must remain adaptive in its design if pinpointing a spawning location in the lower Green River is a priority of the Recovery Program. Colorado pikeminnow Typical of many preliminary investigation studies, a series of factors (funding, implementing new sampling techniques [larval light trapping and the processing of larval samples], environmental conditions [extremely low flows (1994) followed by a high flow year]) required a prioritization of field tasks to meet project objectives. Ultimately, a disproportionate amount of effort was directed at answering the questions of razorback sucker spawning in the lower Green River due to the tenuous status of that species in the upper Colorado River basin. Specific efforts were made to address the Colorado pikeminnow spawning question, but they were less rigorous. There were no collections of adult pikeminnow in the suspected spawning azea throughout this study. In 1994, the sampling for adult pikeminnow was probably timed correctly based on similaz investigations conducted near the Gray Canyon spawning baz (Chart and Lentsch 1998). Unfortunately, low river flows precluded the use of electrofishing that yeaz. In 1995, both electrofishing and trammel nets were used at Millard Canyon, however, the timing may have been pre-mature (based again on sampling neaz the Gray Canyon spawning baz). No larval Colorado pikeminnow were collected below the suspected Millazd Canyon spawning site in 1995. In 1994, 94 juvenile Colorado pikeminnow (40-118 mm TL) were captured downstream of the Green-San Rafael River confluence (RK 156.2-95.3) on 15-17 June. In 1995, eleven larval Colorado pikeminnow and 2 juveniles were captured near the mouth of the San Rafael River in light traps. These collections do not suggest that pikeminnow were spawning at a "new location". We assume these larvae were produced at the Gray Canyon spawning azea (Three Fords rapid is located at RK 251, approximately 100 km upstream of the mouth of the San Rafael River). The results of ISMP sampling in 1994 and 1995 revealed below average concentrations of YOY pikeminnow throughout Reach 3 (RK 193-0.0). In 1995, catch per unit effort was at a ten yeaz low, which must be considered when interpreting the results of this project. 8