7978

• UCREFRP Catalog Number: 7978
• Author: Tyus, H. M.
• Title: Chemoreception, Imprinting, and Propagation of Colorado Squawfish and Razorback Sucker
• USFW Year: 1992
• USFW - Doc Type: a Plan of Study
• Copyright Material: YES

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and Wisby (1951). 1hey suggested that young salmon imprint to the odor of
their natal tributary, store this information in a long-term olfactory
memory, and later use this memory to relocate the stream during spawning
migrations. In the following 40 years, many other workers have tested and
further refined this hypothesis. It is now recognized that fish imprint to a
"home-site olfactory bouquet" which consists of environmental odors that may
include both a geologic and species-specific component (Hasler and Scholz
I983, foster I985). However, our knowledge of the adaptive significance of
migrations and reproductive cycles is poor for all but a few, commercially
important species.

Migration patterns of adult Colorado squawfish are similar year to year.
These movements are presumably an orientation to environmental conditions in
the spawning reaches, and movements of fishes in up- and downstream directions
is suggestive of an olfactory orientation mechanism (Harden-Jones 1968, Hasler
and Scholz 1983). Some behaviors associated with olfactory orientation in
sa1monids were exhibited by Colorado squawfish, and the presence of spring-fed
tributaries and other water inputs in spawning reaches may provide piloting
cues. Tributa~ streams m~ provide 9ross cues for long-distance orientation,
while more subtle cues, unique to specific sites, may be used for egg
deposition (Tyus, In press). Reproductive by-products from previously-hatched
young (foster 1985) may also be included in a home-site olfactory bouquet.
Colorado squawfish larvae may imprint such odors in the areas in which they
develop, and later recognize these odors as migrating adults.

Recaptured and radiota9ged adult Colorado squawfish have demonstrated a
fidelity (repeated return) to the same spawning areas (Wick et a1. 1983, Tyus
1985, in press). However, it has yet to be shown that these fish return to
natal areas for spawning. 1he similarity of their behavior to that of many
other fishes makes it probable that they do so, and this could lead to
reproductive isolation and separate genetic stocks. It is noted that the
maintenance of discreet stocks can be developed through spawning site
imprintin9 and homin9 (Horra11 1981), and thus, specific mi9ration routes and
positive or negative rheotaxis in homing orientation su9gests different
genetic stocks (reviewed by Smith 1985). Some genetic interchange between
stocks may occur from fish that "str~' from one area to another, and could be
important for successful evolution of the species (8aker 1982; Leggett 1984).
It is therefore important t~at the genetic identity of separate stocks of
Colorado squawfish be identified and protected.

Knowledge of the reproductive ecology of the razorback sucker is poorly
known, principally because successful recruitment is 1ackin9 throughout the
Colorado River Basin (Lanigan and 1yus 1989, Marsh and Minckley 1989).
However, razorback sucker migrations have been documented, and there is
compelling evidence that homing behavior occurs as in the white sucker. The
possibility of at least two separate spawning stocks of the razorback sucker
in the Green River basin (Tyus and Karp 1990) suggests that imprinting and
home site selection may be also be important considerations in the recovery of
this fish.

S1UDY ME1HODS AND APPROACH:

Because of the time required to do this work, and the critical need to
demonstrate progress towards recovery of endangered Colorado River fishes, we

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