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y ,- t ~~ - --.--' 7""';;'~~'i "<-:,-~ ( ~tb ''01:10'"''''' : - _.S lii'- "~ ,...~~,."," ... "\.,I!I" ~.,.. "'"..,. , -() " L \. ~ " ~, .., ~ ~j3 I , . I - f'lv $. ICHTHYOLOGICAL NOTES CELlNE AUDET, GERARD J. FITZGERALD AND HELGA GUDERLEY, Departement de Biologie, Faculte des Sciences et de Genie, Universite Laval, Quebec, GIK 7P4, Canada. Accepted 27 APril 1984. Cop,in, 1985(1), pp. 2\~-215 @ 1985 by the American Society of Ichthyologists and Herpetologists HOMING BEHAVIOR NOTED FOR COL- ORADO SQUA WFISH.- The Colorado squawfish, Pt)'chocheilus lucius Girard, a large pis- civorous cyprinid endemic to the Colorado Riv- er Basin, was once widely distributed in the up- per and lower basins. Its abundance declined' notably in the lower basin in the 1930's and' none has been reported there since the 1960's (Minckley, 1973). Natural populations present- ly exist only in the upper basin, where the species has been classified as endangered (US Fish and Wildlife Service, 1974). Migrations of Colorado squaw fish were reported in early accounts (Sig- ler and Miller, 1963; Minckley, 1973) but never documented until 1981 (Tyus et aI., 1984). Since that time two major spawning areas have been identified in the Green River Basin of Colorado and Utah, and Colorado squawfish have been radiotracked over round-trip distances of 400 km in migration to and from these areas. This paper presents evidence for a homing hypoth- esis based upon data from the Green, White and Yampa rivers, 1980-1983. Methods.-Colorado squawfish were captured by electrofishing. Collections were made in April and May so the fish might have time to recover from surgery before the mid-summer spawning seaSOn. The captured Colorado squawfish were placed into a 200 mg/L solution of tricaine methylsulfonate and surgically implanted with radiotransmitter modules. The incision was made laterally, immediately anterior and slight- ly dorsal to the insertion of the right pelvic fin. The incision was closed with 2.0 mm nylon su- tures of triple-tied, individual surgical knots. In 1980, fish were held 5 days to evaluate the suc- cess of the surgery. Thereafter, the fish were released immediately after implantation to re- duce stress (Hart and Summerfelt, 1975). . Four different types of transmitter modules diPped in melted beeswax were used. These ~odules weighed approximately 11 to 23 g in air and 3.5 to 6 g in water. All units were pow- 213 ered by mercury batteries and had a unique signal (frequency vs pulse rate) so that individ- ua] fish could be identified. Radio receiver sets used were Smith-Root RF-40 and SR-40 models, which enabled the investigator to search for all transmitters and to identify any particular transmitter by its emitted radio signal. Omnidi- rectiona] whip and bidirectional loop antennas were employed from boat and airplane (Tyus, 1982). Ii Ii u Ii ~ ~ II ~ II Ii Results and discussion.- Two spawning migra- tions have been identified in the Green River Basin by tracking radio-impl Colorado squawfish. One migration, ide ifie 1981 (Fig. 1) was reconfirmed in 1983 (Fig. 2). 0]- orado squawfish migrated downstream in the Yampa River and upstream from the Green River to spawn in rime/pool habitat of the low- 1Il a: w I- W ::E o ...J ii2 MAY JUNE JULY AUG SEPT MONTH Fig. 1. Migration of 8 radiotagged Colorado squawfish to spawning grounds in the Yampa River, 1981. Each dot represents one radio contact. Con- nected dots represent the movement pattern of one fish. Mouth of Yampa River = 0 km. '19Q1 v,J C7301