Laserfiche WebLink
<br />(:.> <br />C~) <br />...... <br />co <br />~") <br />..:::'"- <br /> <br />Recognizing the potential predation effect channel catfish may have on native fishes, the SJRIP initiated <br />removal of channel catfish, and other nonnative species, from the San Juan River in 1995, Brooks et al, <br />(2000) initiated studies in 1995 evaluating methods for mechanical removal of channel catfish. They used <br />three primary methods: electrofishing, hoop netting, and trot lining. Hoop netting and trot lining were <br />ineffective and they were dropped from the study in late 1995. Nonnative fishes collected during regular <br />adult and juvenile monitoring studies were discarded on the river bank starting in late 1995 (Brooks et al. <br />2000). These efforts resulted in the removal of 12,660 channel catfish and 10,016 common carp from <br />1995 to 1997, However, catch rates for these species did not decline. In fact, they may have increased <br />slightly by 1997 (Brooks et al. 2000, Ryden 2000a). Brooks et al. (2000) and Propst and Hobbes (2000) <br />noted that the channel catfish size structure appeared to change by 1997, when fewer large fish and more <br />smaller fish were caught. This may be a result of electrofishing removal, which is more effective on larger <br />fish. <br /> <br />The data from the 7 -year research period suggest that efforts to date were effective in reducing density of <br />large channel catfish, which food habits studies showed were the most piscivorous, but efforts were not <br />effective in reducing overall abundance of channel catfish in the river. Although the high numbers of this <br />species suggest a concern for predation on native fishes, extensive predation was not verified, It is <br />undoubtedly safe to assume that high numbers of channel catfish will result in predation on native fishes, and <br />efforts to reduce their numbers should be continued if they are effective, In 1997, the SJRIP initiated a <br />program of transporting channel catfish caught in the San Juan River to off-river impoundments on the <br />Navajo Reservation where they were accessible to anglers (Brooks et al. 2000), Nonnative species <br />removal will be continued as part of the long-term monitoring plan. <br /> <br />Propst and Hobbes (2000) noted reduced red shiner numbers in secondary channels during years when <br />a sununer flood event occurred, In 1998, the SJRIP initiated a 3-year study to investigate the timing and <br />size of a sununer flow spike that would reduce red shiner numbers, That study is not complete. <br /> <br />FISH HEALTH <br /> <br />Introduction <br />During 1991, biologists conducting adult monitoring studies on the San Juan River noticed high <br />numbers of abnormalities in the flanneImouth sucker and bluehead sucker collected, Abnormalities <br />included open sores, parasites, and body deformities. Biologists were most concemed with the <br />relatively high number of open sores or lesions on the sides of some of the fishes, especially <br />flanneImouth sucker, This prompted a concern for fish health, and fish health experts joined sampling <br />trips in 1992 (Landye et al. 2000). As fish were weighed and measured during adult monitoring trips, <br />they also were checked for abnormalities (Ryden 2000a). These data (Table 3,7) showed <br />that abnormalities were typically found on less than 2% of the native bluehead sucker and <br /> <br />September 2000 <br /> <br />3-52 <br /> <br />Program Evaluation Report <br />