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Young-of-the- Year (YClY) and Juveniles Larval razorback sucker sampling was not conducted in the San Juan River during the 7-year research period. Some larval fishes were collected during nursery habitat studies, but no larval razorback sucker were collected. However, larval razorback sucker sampling began in 1998 because maturation of the stocked razorback sucker was expected, and two larvae were collected by seining low-velocity habitats (S. Platania, University of New Mexico, Personal Communication). In 1999, seven larvae were collected (S. Platania, University of New Mexico, Personal Communication). These captures verified successful spawning of fish experimentally stocked in the San Juan River. Future studies oflarval habitat use will be needed to determine what habitats this life stage uses. Juvenile habitat use determination also will have to wait until more juveniles are present in the river. It is assumed that both larval and juvenile razorback sucker will select low-velocity habitats and that these habitat; will likely be important for recovery of this species. Other Native Fishes Other native fishes of primary concern in the San Juan River during the 7-year research study were roundtail chub, t1annelmouth sucker, bluehead sucker, and speckled dace. Because of its reduced numbers, roundtail chub is a concern in several parts of the Colorado River Basin, including the San Juan River. It is state-listed as endangered in New Mexico (Propst 1999). Roundtail chub was a target species for thf' SJRIP because it was rare in the San Juan River below Navajo Dam. The other three species were generally common-to-abundant in most of the Upper Basin and in the San Juan River (Table 3.1), although t1annelmouth sucker is rare in some portions of the Lower Colorado River Basin. No radiotelemetry studies of these species were conducted, so specific adult habitat use was not identified. The SJRIP emphasis on the entire fish community, rather than just the endangered fish species, , provided considerable information on the more-common native fishes, such as t1annelmouth sucker, bluehead sucker, and speckled dace. Although common throughout much of the Upper Basin, information on these species was seldom provided in recovery effort reports. The adult monitoring and secondary channel studies showed that bluehead sucker and speckled dace were densest in the cobble substrate-dominated upper portions of the San Juan River. Their density decreased in the middl.e river, and they nearly disappeared in the lower river. Flannelmouth sucker, on the other hand, was not as tied to cobble substrates, and their density continued at relatively high levels further downstream than either bluehead sucker or speckled dace (Propst and Hobbes 2000, Ryden 2000a). The SJRIP studies showed that the habitat used by young of these species varied through the summer and autumn. Flannelmouth sucker, bluehead sucker, and speckled dace young were found in nursery habitats during early summer, but their numbers decreased in these low-velocity habitats in late summer and autumn. This change in habitat use was noticed at other locations, but it was seldom documented to the extent that it was in the San Juan River studies. Studies concerning abundance, general habitat use, and tributary habitat use were also used to devdop the potential for limiting habitat for these species. September 2000 3-12 Program Evaluation Report I I I I I I I I I I I I I I I I I I I