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1. There were 152 fish collections at 139 unique sites made between river miles 141.6 and 2.8 during the 2002 razorback sucker larval fish survey. 2. The 2002 sampling effort yielded 40% fewer fish (n=56,034) as compared to 2001 (n=95,628) but still produced more fish than were taken cumulatively during 1998, 1999, and 2000 (n=45,429) 3. The 152 samples resulted in the collection of fish representing six families and 11 species, with all except five samples producing fish.
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There were 211 fish collections made between river miles 126.1 and 3.0 (=Clay Hills Crossing) under the 2000 razorback sucker larval fish study. The 2000 sampling effort yielded 11,473 fish representing six families and 13 species. Fish taxa present in year 2000 samples but absent from 1998 and 1999 collections were black bullhead, kokanee salmon, bluegill, and largemouth bass. None of these four species are native to the San Juan River. Conversely, roundtail chub and Colorado pikeminnow, both native fish species taken in 1998-1999 samples, were absent from 2000 collections.
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Some nonnative fishes have exhibited different feeding behaviors depending on location. In a study within the Colorado River system, Ruppert et al. (1993) found a relatively high occurrence (15%) of larval fish in stomachs of Cyprinella lutrensis. They compared those results to a study by Jennings and Saiki (1990) who found no larval fish in stomachs of C. lutrensis from the San Joaquin River drainage. The disparity between these studies could be a function of site specific characteristics such as availability of alternative food items, or it could be due to specific behavior and vulnerability of prey. The purpose of our study was to determine if nonnative fishes, primarily C. lutrensis and Pimephales promelas,...
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The 1998 razorback sucker larval fish sampling study was modified from that previously employed to allow for collection of fish over a longer portion of the San Juan River and capture of a considerably larger number of larval fish. Starting in 1998, an inflatable raft was used to travel the river and provide the opportunity to sample habitats that were formerly either inaccessible or unobservable. The primary 1998-1999 collecting method was sampling low-velocity habitats with a fine mesh seine. This sampling technique often yielded more larval sucker at a single site than had been taken cumulatively in the 1997 light-trap samples.
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1. There were 369 fish collections made at 306 unique sites between river miles 141.3 and 2.9 under the auspices of the 2006 larval Colorado pikeminnow and 2006 larval razorback sucker surveys. 2. The 369 collections resulted in the collection of fish representing six families and 15 species with all but ten collections producing fish. 3. In 2006, the riverwide CPUE was 402.3 fish per 100m2 with a total of 50,626 specimens collected. This represents over a two-fold reduction in catch rates compared with 2005.
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