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C'.) c) ...... co co tlannelrnouthsucker. Even with the decline in catch rates, tlannelrnouth sucker remained very abundant and -.J comprised more of the total San Juan River collection than Colorado or Gunnison river collections (Ryden 2000a). More-recent analysis of the catch data indicates that tlannelrnouth sucker density river wide has not changed because the increase in Reach 6 offset the decrease in the other reaches. But numbers of juvenile flannelrnouth sucker declined from 1992 to 1993, and they have not changed much from that time (K. Lawrence, Ecosystems Research, Inc., Personal Communication). Flannelrnouth sucker adults are the "generalists" of the Colorado River Basin, and they are found in a variety of habitats, including riffles, runs, pools, and eddies (Holden and Stalnaker 1975, McAda 1977). They use cobble bars throughout the rivers for spawning and are found on the same bars razorback sucker use for spawning. Larval and YOY flannelrnouth sucker are found in backwaters and other low-velocity habitats in early summer. Abundance of the young declines as the summer progresses, likely because of mortality and a shift in habitat use to swifter main channel habitats. Collections of flannelrnouth sucker in the San Juan River showed the same generalized habitat use (Lawrence 1999). Juveniles in the San Juan River were correlated with shoreline slackwater habitats in the spring and cobble-type habitats in the autumn (Lawrence 1999). The change in habitat use between juvenile and adult flannelrnouth sucker was seen in their use of San Juan River secondary channels (Propst and Hobbes 2000). During high flow periods, secondary channels provided riffle and run habitat, and adult and larger juvenile flannelrnouth sucker were the most-commonly collected fish in secondary channels. Ripe fish were collected, thus suggesting spawning also occurred in secondary channels. As flows receded in late summer and autumn, habitats in secondary channels became primarily low-velocity types, and larger flannelrnouth sucker were seldom collected there. Although reduced in numbers, YOY flannelrnouth sucker utilized the low-velocity habitats of secondary channels during that time (propst and Hobbes 2000). Flannelmouth sucker used most available habitats, and no key habitats were identified. Bluehead Sucker Bluehead sucker was the third most-abundant fish in the San Juan River, and it was most abundant in the upper portions of the river where cobble substrates predominated. Bluehead sucker was most abundant in Reach 6, but their abundance decreased somewhat in the remainder of the river during the 7-year research period (Ryden 2000a). Adult and juvenile bluehead sucker were typically found in cobble substrate riffle and run habitats in the San Juan River (Ryden 2000a). Spawning appeared to occur on cobble bars, sirrrilar to other native suckers. Adult and juvenile abundance in the San Juan River was positively correlated with cobble-type habitats, particularly riffles (Lawrence 1999). Larvae and YOY were found in low-velocity habitats in the summer, but sirrrilar to flannelrnouth sucker young, they tended to disappear from these habitats by late summer and autumn (Archer and Crowl 2000a). Sirrrilar to tlannelrnouth sucker, bluehead sucker habitat use was characterized by their seasonal use of secondary channels. Adults and larger juveniles used secondary channels during higher-flow periods when riffle and run habitats were available, and reduced numbers of young used them during low-flow periods when low- velocity habitats predominated (propst and Hobbs 2000). Key habitats for bluehead sucker were cobble substrate riffles and runs. September 2000 3-15 Program Evaluation Report