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<br />(0 <br /> <br />~ velocity habitats such as eddies and pools used by adult fish and backwaters used by young fish. <br />~ Flows will be recommended to enhance habitat for the endangered fishes at the end of the 7-year <br />I c2 research period. Current research suggests fairly normal (high) spring peaks and low summer flows <br />C;, maximize the amount of habitat available for endangered and other native fish. <br /> <br />5.3. Identify, Protect, and Restore the Endangered Fish Species of the San Juan <br />River Basin and Manage the Native Fish Community. <br /> <br />Ongoing studies are identifying the structure, status, and trends of the San Juan River Basin fish <br />community. Of the larger species that inhabit mainchannel habitats, native suckers are numerically <br />predominate, while nonnatives dominate the small fish species assemblage that utilize low velocity <br />near shore habitats such as backwaters and secondary channels. Changes in the fish community <br />between years have been noted, but no clear pattern of change related to flow has been identified. <br />Diseases and parasi~es of the fish community have been studied and some areas within the San Juan <br />System exhibit an incidence of relatively poor fish health. The reasons for this are not known. <br /> <br />Except for a slight increase in numbers of young Colorado squawfish in 1993, reproductive success <br />of Colorado squawfish has been poor since the SJRRIP studies were initiated in 1991. Higher <br />numbers in 1993 may have been in response to relatively high flows during that year. The need for <br />augmentation of the rare fish populations has been discussed and experimental augmentation of the <br />razorback sucker population was initiated in 1994. <br /> <br />5.4. Determine the Role(s) of Nonnative Fish Species in the Decline of Native Fish <br />Species and Implement Corrective Actions. <br /> <br />Studies have been undertaken to examine nonnative fish use of the San Juan System and how they <br />may be affecting the native fish. Population trends and food habits of several nonnative species have <br />been studied. Nonnative fish are abundant in the system and they tend to dominate in lower velocity <br />habitats frequented by small fish. Nonnative fish ab,undance dropped from 1991 to 1994, and native <br />fish abundance has increased, suggesting that the flows that have been provided for the Program may <br />be helping the native species. In 1995, a study to evaluate the potential for mechanical removal of <br />channel catfish was initiated, but success was poor so the study was not continued in 1996. <br /> <br />5.5. Determine the Occurrence, Extent, and Role(s) of Water Quality Degradation <br />and Contaminants in the Decline of the Endangered Fish Species and Identify <br />and Implement Corrective Actions. <br /> <br />A number of studies examined both water quality and contaminant issues related to rare fish. A <br />historical review of contaminants has been completed. The historical review reported that selenium <br />and polycyclic aromatic hydrocarbons (P AHs) were the most likely contaminants for the fish <br />community. Studies of the toxicity of the San Juan River water to native fish have shown that water <br />quality (contaminants) in some areas have the potential to affect Colorado squawfish, razorback <br />sucker, and flannelmouth sucker. <br /> <br />San Juan River Recovery Implementation Program <br />Summary Report <br /> <br />Hi <br /> <br />17 January 1997 <br />PR-576-2 <br />