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a? DLo ;1'(- L&lz_ 1-?-- 4?-. }- . ck 9 7a5 Transactions of the American Fisheries Society 135:539-544, 2006 [Note] American Fisheries Society 2006 DOI: 10.1577ff05-204.1 Distribution and Movement of Humpback Chub in the Colorado River, Grand Canyon, Based on Recaptures CRAIG P. PAUKERT,*1 LEWIS G. COGGINS, JR., AND CHRISTOPHER E. FLAccus U.S. Geological Survey, Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, 2255 North Gemini Drive, Flagstaff, Arizona 86001, USA Abstract.-Mark-recapture data from the federally endan- gered humpback chub Gila cypha in the Colorado River, Grand Canyon, were analyzed from 1989 to 2002 to determine large-scale movement pattems and distribution. A total of 14,674 recaptures from 7,127 unique fish were documented; 87% of the recaptures occurred in the same main-stem river reach or tributary as the original captures, suggesting restricted distribution by most fish. A total of 99% of all recaptures were from in and around the Little Colorado River (LCR), a tributary of the Colorado River and primary aggregation and spawning location of humpback chub in Grand Canyon. Time at liberty averaged 394 d, but some fish were recaptured near their main-stem capture location over 10 years later. Proportionally fewer large (>300-mm) humpback chub exhibited restricted distribution than small (G200-mm) fish. However, several fish did move more than 154 km throughout Grand Canyon between capture and recapture, suggesting that limited movement occurs throughout Grand Canyon. The majority of the recaptured fish remained in or returned to the LCR or the Colorado River near the LCR. Although many large-river fishes exhibit extensive migrations to fulfill their life history requirements, most of the humpback chub in Grand Canyon appear to remain in or come back to the LCR and LCR confluence across multiple sizes and time scales. Detecting trends in the overall abundance of this endangered fish in Grand Canyon can probably be accomplished by monitoring the area in and around the LCR. The humpback chub Gila cypha is a federally endangered species with only six remaining popula- tions, the largest population located in the Little Colorado River (LCR) and Colorado River in Grand Canyon (Kaeding and Zimmerman 1983; USFWS 2002). Like many other big-river fishes in the southwestem United States, humpback chub popula- tions are declining because predation, competition from nonnative fish, large-scale river regulation, or a combi- nation thereof altered temperature and flow regimes (Minckley et al. 2003). Recent research on humpback * Corresponding author: cpaukert@ksuedu 1 Present address: U.S. Geological Survey, Kansas Cooper- ative Fish and Wildlife Research Unit, 205 Leasure Hall, Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA. Received August 5, 2005; accepted November 29, 2005 Published online March 28, 2006 chub has focused on population estimation and trends to meet recovery goals of the U.S. Fish and Wildlife Service (USFWS 2002; Coggins et al. 2006). The LCR is the largest tributary to the Colorado River in Grand Canyon (Figure 1) and is the primary spawning location for humpback chub (Kaeding and Zimmerman 1983; Douglas and Marsh 1996), these fish inhabiting the lower 14.75 km. Recruitment of humpback chub likely does not occur (or is extremely limited) in the main-stem Colorado River because of cold water temperatures (Kaeding and Zimmerman 1983). Humpback chub from the main stem move into the LCR to spawn, some adults remaining in the LCR for extended periods of time other than spawning (Douglas and Marsh 1996; but see Gorman and Stone 1999; Coggin et al. 2006). Humpback chub movement and distribution have been previously examined with more spatially or temporally limited data sets that recorded recaptures only in the LCR, its inflow, or both (Kaeding and Zimmerman 1983; Douglas and Marsh 1996; Gorman and Stone 1999) or using telemetry with smaller sample sizes (Keading et al. 1990; Valdez and Hoffnagle 1999). In addition, these studies focused on short time frames (usually under 1 year or fewer seasons across 2 or fewer years). To our knowledge, no one has evaluated site fidelity over a long (>10-year) time period with sample sizes (>I 0,000 recaptures) as large as this study. Large-river fishes typically migrate long distances, presumably to meet the life history requirements of adults such as spawning (e.g., Pellett et al. 1998; Paukert and Fisher 2001), and this also occurs in adult desert river fishes (Tyus 1991; Modde and Irving 1998). However, the scale at which distribution and movement is evaluated also affects how conservation and management measures are implemented (Fausch and Young 1995; Hay et al. 2001). Previous studies of endangered or threatened desert fishes in the south- western United States have shown mixed results. Humpback chub show high fidelity (using short-term telemetry transmitters) in main-stem riverine popula- tions (Keading et al. 1990; Valdez and Hoffnagle 1999), whereas bonytail Gila elegans have less fidelity during spawning (Keading et al. 1990). Colorado 539