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T ,. ~ r ) ,t * J YLiS r Me MeA.- lygLf THE SOUTHWESTERN NATURALIST 29(3):289-299 \\rJ)~ 1\ , ~":\ 1 n \ 1:)1 ',J j , , t:jl/1? Y- ()l~ (/cI~ _:. 00, AUGUST 28, 1984 i i ().!-I MIGRATION, MOVEMENTS AND HABITAT PREFERENCES OF COLORADO SQUAWFISH, PTYCHOCHEILUS LUCIUS, IN THE GREEN, WHITE AND YAMPA RIVERS, COLORADO AND UTAH HAROLD M. Tyus AND CHARLES W. McADA AosTRACT.-A total o[ 31 Colorado squawfish, Ptychocheilus lucius, were collected [rom the Green River in 1980 and the Green, White and Yampa rivers in 1981. The fish were surgically implanted with radiotransmiller modules and their movement monitored [or up to five months each year. Two movement pallerns were linked to fish maturity: mature fish were highly mobile; immature fish were sedentary. A spawning migration of up to 205 km one-way was documented in 1981. Fish migrated upstream and downstream to reach a common spawning ground in the lower Yampa River canyon. Diel studies indicated no diel rhythm in movement existed until after spawning, when the fish were more aClive [rom 0800-1200 h. Colorado squawfish were monitored primarily in shoreline habitat over sand substrates. There were significant differences recorded [or water depths and velocities selected by Colorado squaw[ish between the Green, White and Yampa ,;vers, but no difference occurred between 1980 and 1981 values recorded in the Green River. 'i The Colorado squawfish, PtychocheiLus Lucius Girard, endemic to the Colorado River Basin, was once widely distributed in the upper and lower Colorado River basins. A decline in abundance was noted in the lower basin in the 1930's (Miller, 1961) and none have been reported there since the 1960's(Minckley, 1973). Natural populations presently exist only in the upper basin, where it has been classified as endangered by the Fish and Wildlife Service (1973, 1974). The Green River and its two larger tributaries, the Yampa and White rivers in Colorado and Utah, contain the largest known concentration of Colorado squawfish. Early accounts suggested its migration (Sigler and Miller, 1963); however, these accounts have not been previously substan- tiated. Spawning requirements are known only from laboratory work (Hamman, 1981) and spawning has never been documented in nature (Minckley, 1973). This study was conducted as part of the Colorado River Fishery Project, an interagency effort to obtain data on the life history requirements of the pndangered fish fauna of the upper Colordo River basin. The increasing need for water in the upper basin may soon result in the extinction of the Colorado squawfish due to the construction of dams and alteration of historic flow regimens. This study documents long distance potamodrom- DUS (Myers, 1949) migrations of the Colorado squawfish, its habitat preferences and provides information about spawning requirements. METHODS.-Colorado squawfish were collected primarily by electrofishing but some were also collected by seining and trammel nelling. Sampling was conducted in the Green River in April and May 1980 and in the Green. White and Yampa rivers in April and May 1981 (Fig. I). Collenions w(~rf' made early in tht, year so [ish mig-hl have time to Tl'('over from surg-(~ry before toe mid.summer spawning season. . . -\ -c. f 'if) "'~ :C'<:- ~0 .+" ~ -- ~ ~-Lc-. , -" ~ ,.fZ ~ 6 ~ t r ':. =i. rr- P ~ \CJ.-......l. .~ w C) .()J