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<br />
<br />ICHTHYOLOGICAL l\OTES
<br />
<br />215
<br />
<br />proves the existence of an olfactory imprinting
<br />mechanism (Hasler and Scholz, 1983) for Col-
<br />orado squawfish, conditions at the two spawning
<br />grounds suggest that such a mechanism could
<br />be in use. Field observations of the two known
<br />spawning grounds in the Green River Basin in-
<br />dicate these canyon areas are geohydrologically
<br />different from those immediately upstream, and
<br />Colorado squawfish appear to select river can-
<br />yons that receive freshwater input from sand-
<br />stone/limestone seeps for spawning. The fish
<br />may use the input of groundwater in these lo-
<br />cations as a means of orientation, and I suggest
<br />the Groundwater Seepage Hypothesis, pro-
<br />posed by Harden-Jones (1981), be considered
<br />as a possible mechanism. If such a mechanism
<br />is operating, the larval squawfish would have to
<br />be imprinted at an early stage, since they drift
<br />downstream soon after hatching.
<br />The Colorado squaw fish may provide new in-
<br />sights into the homing mechanism of fishes, and
<br />several mechanisms (Leggett, 1977) may be im-
<br />plicated in the ability of this species to home to
<br />specific sites. The use of olfaction, genetic mem-
<br />ory (Nordeng, 1977) and learning should be
<br />further investigated. There is a danger, how-
<br />ever, that this endangered fish is continuing to
<br />decline and may be extirpated from its remain-
<br />ing range before such investigations can be
<br />made. It appears that strong homing behavior
<br />observed thus far in the Green River Basin is
<br />restricted to only a few sites of relatively un-
<br />disturbed spawning habitat that lie upstream
<br />from productive nursery areas. This behavior
<br />may be lacking in other areas of occupied Col-
<br />orado squawfish range where spawning habitat
<br />has been cut off by dams, where nursery areas
<br />are poor, or where river management has de-
<br />graded habitat and fostered exotic fish com-
<br />petitors. Because optimal reproduction may be
<br />~ependent on long distance migration, obstruc-
<br />t~ons to stream passage should be viewed as par-
<br />ticularly threatening. If larval Colorado squaw-
<br />fish imprint to the spawning grounds they must
<br />do so at an early age. Stocking of hatchery-
<br />~eared squaw fish should be avoided until more
<br />In~ormation about homing and imprinting is ob-
<br />ta.lned. Hatchery-reared fish would compete
<br />With residents for food and space but may not
<br />have the ability to home to suitable habitat and
<br />sUccessfully reproduce. If this is true, the intro-
<br />duction of hatchery-reared Colorado squaw fish
<br />Would hasten the demise of this interesting
<br />species.
<br />
<br />Acknowledgments.- The information presented
<br />was obtained from US Fish and Wildlife Service
<br />Studies funded, in part, by the Bureau of Rec-
<br />lamation and the National Park Service. Several
<br />other federal employees aided in obtaining field
<br />data, including C. W. McAda, E. J. Wick, D. L.
<br />Skates, J. J. Krakker and W. B. Harned. The
<br />states of Utah and Colorado provided logistical
<br />support.
<br />
<br />LITERATURE CITED
<br />
<br />GERKI~G, S. 1959. The restricted movement of fish
<br />populations. Bio\. Rev. 34:221-242.
<br />HARDEN-JONES, R. F. 1981. Fish migration: Strategy
<br />and tactics, p. 139-165. In: Animal migrations. D.
<br />J. Aidley (ed.). Semin. Ser. 13. Soc. for Exp. Bio\.
<br />Cambridge Univ. Press, New York.
<br />HART, L. D., AND R. C. SVMMERFELT. 1975. Surgical
<br />procedures for implanting ultrasonic transmitters
<br />into flathead catfish (PyLodictis olivaris). Trans. Amer.
<br />Fish. Soc. 104:56-59.
<br />HASLER, A. D., AND A. T. SCHOLZ. 1983. Olfactory
<br />imprinting and homing in salmon, p. 3-38. In: Zoo-
<br />physio\. 14. Springer-Verlag, New York.
<br />LEGGETT, W. C. 1977. The ecology of fish migra-
<br />tions. Ann. Rev. Eco\. Syst. 8:285-308.
<br />MILLER, W. H., H. M. Tyvs AND L. R. KAEDING.
<br />1983. Colorado River fishes monitoring project.
<br />First Annual Report. US Fish and Wild\. Servo Salt
<br />Lake City, Utah. 23 pp.
<br />MINCKLEY, W. L. 1973. Fishes of Arizona. Arizona
<br />Game Fish Dept. Phoenix, Arizona.
<br />MYERS, G. S. 1949. Usage of anadromous, catadrom-
<br />ous and allied terms for migratory fishes. Copeia
<br />1949:89-97.
<br />NORDENG, H. 1977. A pheromone hypothesis for
<br />homeward migration in anadromous salmon ids. Oi-
<br />kos 28:155-159.
<br />SIGLER, W. F., AND R. R. MILLER. 1963. Fishes of
<br />Utah. Utah State Dept. Fish and Game. Salt Lake
<br />City, Utah.
<br />TYl;s, H. M. 1982. Fish radiotelemetry: theory and
<br />application for high conductivity rivers, US Dept.
<br />Int., Fish Wild\. Servo FWS/OBS-82/38. Washing-
<br />ton, DC. 26 pp.
<br />TYl;s, H. M., E. J. WICK AND D. L. SKATES. 1984. A
<br />spawning migration of Colorado squawfish (PI)'ch-
<br />ocheilus Lucius) in the Yampa and Green rivers, Col-
<br />orado and Utah, 1981. Proc. Desert Fish. Counc.
<br />13.
<br />U>;ITED STATES FISH AND WILDLIfE SERVICE. 1974.
<br />Colorado squawfish; determination as an endan-
<br />gered species. Federal Register 45 27710-17713.
<br />
<br />H. M. Tyus, US Fish and VI.'ildlife Sm'ice, 447 E.
<br />,Wain St., Vernal, Utah 84078. Accepted 18
<br />April 1984.
<br />
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