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bonytail/h. Channel catfish was the only common non-native fish captured in trammel nets; its - capture rate was 0.50 fish/h. The few trammel net sets made in Lodore Canyon captured few fish; little habitat was available for effective trammel netting there. - We examined differences in capture rates of chubs with nets set in day compared to night. Day and night sets captured roundtail chubs at about the same rate, 0.52 (SE = 0.089, N = - 108 fish) and 0.51 (SE = 0.055, N = 182 fish) fish/h, respectively. Nighttime capture rate for humpback chub was 0.022 fish/h (SE = 0.008, N = 7) and higher than the 0.005 fish/h capture - rate for daytime (SE = 0.005, N = 1), but numbers of fish captured was low so no statistical tests were performed. Day and night sets captured bonytail at about the same rate, 0.37 (SE = 0.37, N - = 2 fish) and 0.29 (SE = 0. 11, N = 7 fish) fish/h, respectively; number of fish captured was also low for bonytail. - Equivalent day and night time capture rates for roundtail chub were surprising, given that most chub sampling programs target crepuscular dusk and dawn times. Average capture rate of - roundtail chub in Whirlpool Canyon trammel net samples was higher than average capture rate for roundtail chub in the Black Rocks, Colorado River, 1998 to 2000 (McAda 2002). Humpback - chub was captured mostly at night, but capture rates for it and bonytail were small so veracity of day:night differences in capture rates was difficult to assess. Channel catfish was sometimes • very abundant in trammel net samples, reaching catch rates of 8 to 15 fish/h compared to a maximum of 4 fish/h for roundtail chub. Large catches of channel catfish sometimes inhibited - additional trammel-net sampling for chub due to the long time required to clear nets of fish. Selectivity and relative inefficiency of electrofishing gear compared to trammel nets to • sample chub in deep pools of Whirlpool Canyon was evident. For example, during several electrofishing trips a large pool near Stateline Campground was sampled, but only one or no • chub were collected. Sampling the same pool with six trammel nets on three separate nights in October 2003 yielded 50, 48, and 28 roundtail chub. Similar results were obtained in the - relatively deep upper portion of Whirlpool Canyon, where few or no roundtail chub were captured with electrofishing gear on several occasions and subsequent sampling with up to six trammel nets yielded up to 40 roundtail chub in a single night. Although electrofishing is a • 46