Intermittent or ephemeral streams make up a large percentage of all stream habitats and may have significant roles in spawning, foraging, refugia, and early life history habitat for many fishes. From 2015 to 2017 we examined the use of Cottonwood Creek, an intermittent tributary in the Gunnison River basin, Colorado, by spawning Flannelmouth Sucker Catostomus latipinnis, Bluehead Sucker C. discobolus, and Roundtail Chub Gila robusta. We used combinations of a stream‐spanning picket weir and PIT‐tag antennae near the mouth of the creek to determine fish movement in and out of the stream, which was more effective for the suckers than for Roundtail Chub. Large numbers of suckers used the stream each year despite very different flow regimes. The timing of initial fish entry varied by 6 weeks across 3 years of study from March 17 to May 6. Immigration was only loosely and inconsistently correlated to abiotic factors (various stream temperature metrics and discharge) among years and was most heavily dependent on the presence of sufficient water in the stream to permit fish passage. Average residency times of suckers ranged from 26 to 37 d depending on year and species, and spawning fish lost 10–18% of their body weight depending on species and sex. Both sucker species displayed a high level of annual site fidelity—61–71% of fish returned the year after being tagged. Larval drift was sporadic and many larvae failed to evacuate the stream before flow ceased each year. While further research is needed to assess the overall recruitment contribution from Cottonwood Creek to the regional population, this study revealed use of an intermittent tributary by thousands of native Colorado River fishes, highlighting the importance of nonperennial waters for the completion of the life histories of some large‐river fish species.

Passive integrated transponder (PIT) tags, commonly used to individually identify fish, are assumed to not hinder survival or alter the behavior of the fish and to be retained throughout the duration of the study. While these assumptions have been verified for many species, other species have exhibited poor retention or survival, or altered behavior. In this study, we evaluated short‐term PIT tag retention and recapturability of PIT‐tagged fish in wild populations of migrating and spawning Bluehead Sucker Catostomus discobolus and Flannelmouth Sucker C. latipinnis. We trapped fish as they entered a spawning tributary of the Gunnison River near Delta, Colorado, USA. We abdominally injected 12.5 × 2.1 mm PIT tags and externally marked 2,645 fish; another 2,660 fish were given an alternative external mark but were not PIT‐tagged. When we recaptured fish as they exited the tributary, we found a PIT tag retention rate >99% and recaptured a greater proportion of PIT‐tagged fish than of control fish for both species. We did not identify any tag loss in females, suggesting that tags were not expelled with eggs while spawning. Abdominally injected PIT tags are an effective way of marking these species. Received November 22, 2016; accepted February 26, 2017 Published online April 18, 2017