San Juan River Recovery Implementation Program Summary Report 1991-97

Home Browse Search

areas have been verified. Introduction of young Colorado squawfish has shown that substantial habitat exists for juvenile fish. No wild razorback sucker have been found in the San Juan River since 1988, so fish that were produced from the San Juan lineage were introduced into the river in 1994 for study purposes. Subreaches important to these fish have been identified. The studies have shown that the San Juan River has a limited number of lower velocity habitats, such as the eddies and pools used by adult fish and backwaters used by young fish, but that young Colorado squawfish are using a variety of low velocity habitats that are available in the river. Current research suggests fairly normal (high) spring peaks and low summer flows maximize the amount of habitat available for endangered and other native fish. A Flow Recommendation Report is currently being worked on and will be available in draft form in early 1998. 5.3. Identify, Protect, and Restore the Endangered Fish Species of the San Juan River Basin and Manage the Native Fish Community. � I Ongoing studies are identifying the structure, status, and trends of the San Juan River Basin fish community. Of the larger species, native suckers (i.e., flannelmouth sucker, bluehead sucker) numerically predominate mainchannel habitats and secondary channel habitats during high flow periods, while nonnative species dominate the small fish assemblage that uses low- velocity near - shore habitats such as the backwaters of mainchannel habitats and secondary channels during low flow periods. Changes in the fish community between years have been noted, but no clear pattern of change related to flow has been identified. Diseases and parasites of the fish community have been studied, and some areas within the San Juan System exhibit an incidence of relatively poor fish health, but health does not appear to be a major concern for fish in the San Juan River. Except for a slight increase in numbers of young Colorado squawfish in 1993, reproductive success of Colorado squawfish has been poor since the Program studies were initiated in 1991. Higher numbers of Colorado squawfish in 1993 may have been in response to relatively high flows during that year. The need for augmentation of the rare fish populations has been discussed, and experimental augmentation of the razorback sucker population was initiated in 1994. Young Colorado squawfish were stocked into the river in 1996 and 1997 in order to study habitat availability. In 1997 a draft Genetics Management Plan for the two endangered species was proposed, and an Augmentation Plan for Razorback Sucker was completed. Stocking of razorback sucker for augmentation, rather than experimental purposes, was initiated following the guidelines of the plan in September 1997. Adult Colorado squawfish were also stocked experimentally in the upper San Juan River in September 1997. The experimental stockings that have occurred since 1994 have been very successful, and stocked fish are now found during all sampling periods. 5.4. Determine the Role(s) of Nonnative Fish Species in the Decline of Native Fish Species and Implement Corrective Actions. Studies have been undertaken to examine how nonnative fish use the San Juan System and how they may affect native fish. Population trends and food habits of several nonnative species have been studied. Nonnative fish are abundant in the system, and they tend to be numerically dominant in lower velocity habitats frequented by small fish. Nonnative fish abundance dropped during the period from 1991 to 1994, but has increased since that time, especially in the lower portion of the river. One possible reason for this increase in nonnative fish numbers is the improved access from San Juan River Recovery Implementation Program December 1997 Summary Report III PR -602 -1