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492 The StYltthwestern Naturalist vol. 53, no, 4 individuals occupying flooded mouths of tribu- taries and larger fish (mean total length = 221 mm) occurring in flowing water habitat, including riffies, runs, shorelines, and eddies. Trammel-net sets during our study captured bony tails in 2004 and 2005 at a higher rate during the day (0.63 fish/h, SE = 0.15, n = 23 fish) than at night (0.26 fish/h, SE = 0.11, n = 23 fish). Rates of capture of roundtail chubs in 2002-2005 were similar in the day (0.50 fish/h, SE = 0.068, n = 123 fish) and night (0.46 fish/h, SE = 0.053, n = 195 fish), and each was similar to the capture rate for bony tails in daytime. Fewer humpback chubs were captured during the day (0.009 fish/h, SE = 0.008, n = 2) than at night (0.019 fish/h; SE = 0.006, n = 7) in 2002-2005. Frequency of dorsal-anal-fin-ray counts of bony- tails were 9/10 (n = 1),10/10 (n = 17),10/11 (n = 5), 11/10 (n = 8), and 11/11 (n = 3). Roundtail and humpback chubs typically have dorsal-anal-fin-ray counts of 9/9 and 9/10, respectively (Douglas et al., 1998), and bony tails are typically 10/10 (Holden and Stalnaker, 1970), although 5 of 9 presumed humpback chubs from \VhirlpooI Canyon had a 9/9 count. We captured a smallmouth bass f'vlicropterus dolomitm (330 mm total length) in 2004 that had consumed a bony tail. The partially digested specimen, ca. 225 mm total length (68% of the length of the smallmouth bass), was noted because the caudal fin was protruding from the esophagus of the smallmouth bass. Another predation event was noted in summer 2005, when a smallmouth bass (34] mm total length) captured just downstream of the Echo Park boat ramp preyed on a bony tail that was 211 mm in total length (62% of the total length of the smallmouth bass). Bony tails captured in 2002-2005 with all gears ranged in size ti-om 196 to 336 mm in total length; mean total length was 259 mm and the modal size class was 251-275 mm total length. More than one-half (53%) of bonytaiIs stocked in 2002-2005 that were individually measured before release were ::;225 mm in total length, a size apparently susceptible to predation by larger smallmouth bass. Bony tails of all sizes would be susceptible to predation by larger-bodied preda- tors including the nonnative northern pike Esox Lucius or the native Colorado pikeminnow Plychocheilus lucius. Historically widespread and abundant bony- tails were rare in the Lower Colorado River Basin by the 1970s, with only a few large and old individuals remaining in main-stem reselVoirs, such as Lake Mohave (Jordan, 189]; Minckley, 1973; Behnke and Benson, 1983; United States Fish and \^iildlife Service, 2002). In the Upper Colorado River Basin, bony tails remained rela- tively widespread and common in the lower Yampa River and the Green River downstream of the Yampa River in Dinosaur National Monu- ment from 1963 to 1967, when Vanicek and Kramer (1969) collected 67 individuals >200 mm in total length. During the same period, they collected 49 roundtail chubs >200 mm total length, and 217 smaller chubs, some of which were presumably bony tails (they did not differentiate round tail chubs and bony- tails 200 mm in total length or smaller). By 1967-1973, bonytaiIs in the Upper Colorado River Basin were only in the lower Yampa and Green rivers and were rare, with only 36 individuals collected in extensive basin-wide sampling (Holden and Stalnaker, 1975a, 1975b). As Behnke and Benson (1983:22) point- ed out, "If it were not for the stark example provided by the passenger pigeon, such rapid disappearance of a species once so abundant would be almost beyond belie[" Negative effects of altered flows and reduced water temperatures downstream of Flaming Gorge Dam were postu- lated as main causes for the demise of bonytails in affected reaches of the Green River, but as Kaeding et al. (1986) suggested, reductions in populations of bonytails also occurred in the Colorado River and other reaches apparently little affectcd by tcmpcraturc reductions or othcr dam-associated factors. Also, the congcneric roundtail chub and humpback chub survived in somc reaches where bonytails were once com- mon, so spccific mcchanisms for the ubiquitous decline of wild bonytails remain clusive. Bony tails stocked from hatcheries into the Grcen River study area suffered a fatc similar to their wild counterparts. We documented that hatchery-reared bonytails survived for short pcriods in thc \vild, but they did not appear to sUl\ive over wintcr because we captured no fish released in 2002-2005 in subsequcnt years. We feel confident in our ability to detect presence of bony tails in our study area because we used an array of gears in a widc variety of habitat types in all seasons except winter. Alternatively, it is possible that most bony tails moved out of the study arca and survived, but additional sampling