7971

• UCREFRP Catalog Number: 7971
• Author: Tyus, H. M.
• Title: Evidence for Homing in Colorado Squawfish,
• USFW Year: 1985
• Copyright Material: NO

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to a specific site (Gerking 1959) - has been most dramatically demon-
strated in salmonids (Harden-Jones 1981) and most studies of potamo-
dromous species only document short distance movements of a few kil-
ometers. The movement patterns of Colorado squawfish (Figure 1-3)
demonstrate long distance homing and their behavior is similar in many
ways to that observed in migrating salmonids, including positive and
negative rheotaxis in orienting to spawning grounds (Harden-Jones 1968,
Hasler and Scholz 1983) and "overshooting and backtracking" (Delacy et
al. 1969, Hasler and Scholz 1983).
Olfaction appears to be commonly used by fish species for nav-
igational 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 radiote-
lemetered squawfish even though the fish move freely within an area of
several miles. These observations are in agreement with those by Hasler
and Scholz (1983) that conspecific odors act as generalized attractants
and they found that salmon responded more strongly to odors of other
salmon at the end of spawning season than they did to imprinting odors.
Although there is no experimental evidence to date that confirms or
disproves the existence of an olfactory imprinting mechanism (Hasler and
Scholz 1983) to explain the migration patterns observed for Colorado
squawfish, conditions at the two spawning grounds suggest that such a
mechanism could be in use. Field observations of the two known spawning
grounds in the Green River basin indicate these canyon areas are geohy-
drologically different from those upstream, and Colorado squawfish spawn
in river canyons that receive freshwater input flowing from sand-
stone/limestone seeps. The fish may use the input of groundwater in
these locations as a means of orientation, and I suggest the Groundwater
Seepage Hypothesis, proposed by Harden-Jones (1980), be considered as a
possible mechanism. If such a mechanism is operating, the larval squaw-
fish would have to be imprinted at an early stage, since they drift
downstream soon after hatching.
The Colorado squawfish may provide new insights into the homing
mechanism of fishes, and several mechanisms (Leggett 1977) may be implic-
ated in its ability to home to specific sites. The use of olfaction,
genetic memory (Nordeng 1977) and learning should be further investigated.
There is a danger, however, that this endangered fish is continuing to
decline and may be extirpated from its remaining range before such
investigations can be made. It appears that the strong homing behavior
observed thus far in the Green River Basin is restricted to only a few
sites of relatively .undisturbed spawning habitat that lie upstream from