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~ ,I: , ,- 214 COPELI\., 1985, NO.1 (/l a: w ~ w ~ ~ " MAY JUNE JULY AUG SEPT MONTH Fig. 2. Migration of 8 radiotagged Colorado squawfish to spawning grounds in the Yampa River, 1983. Each dot represents one radio contact. Con- nected dots represent the movement pattern of one fish. Mouth of Yampa River = 0 km. er Yampa River Canyon during both years. Another migration to a spawning site in Gray Canyon of the Green River was suspected in 1981 but not confirmed until fish were moni- tored in 1982 and 1983 (Fig. 3). Colorado squawfish also displayed both upstream and downstream movement (positive and negative rheotaxis) in migrating to the spawning site. A fidelity to the Yampa River spawning site was demonstrated in 1983, when two ripe Colorado squawfish tagged there in 1981, and one tagged there in 1982, returned to the same location for spawning. Potamodromous migrations (Myers, 1949) of North American riverine fishes have received little study in comparison with the information developed for anadromous forms. Until now, homing-a regular movement to a specific site (Gerking, 1959)-has been most dramatically demonstrated in salmonids (Harden-Jones, 1981) and most studies of potamodromous species only document short distance move- ments of a few kilometers. The movement pat- terns of Colorado squawfish (Figs. 1-3) dem- onstrate long distance homing and their behavior is similar in many ways to that ob- served in migrating salmonids, including posi- tive and negative rheotaxis in orienting to spawning grounds (Harden-Jones, 1981; Hasler (/l a: w ~ w ::I o ...J ~ ~--::-^~ 1981 --:---0::_ 1982 --. '983 .J--c--- APR MAY JUNE JULY AUG SEPT MONTH Fig. 3. Migration of 7 radiotagged Colorado squaw fish to spawning grounds in the Green River, 1981-83. Each dot represents one radiocontacl. Con- nected dots represent the movement pattern of one fish. Mouth of Green River = 0 km. and Scholz, 1983) and "overshooting and back- tracking" (Hasler and Scholz, 1983). Olfaction appears to be commonly used by fish species for navigational purposes and is more widespread than formerly believed (Leggett 1977). The initiation of spawning appears to hasten the arrival of other Colorado squawfish to the spawning area, and collections of ripe Colorado squawfish coincide very well with the location of radio-telemetered squaw fish even though the fish move freely within an area 01 several miles. These observations are in agree. ment with those by Hasler and Scholz (1983: that conspecific odors act as generalized attrac. tants and they found that salmon respondec more strongly to odors of other salmon at th( end of spawning season than they did to im- printing odors. Although there is no experi mental evidence to date that confirms or dis.