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Juvenile coho salmon were exposed to morpholine or phenethyl alcohol (p-alcohol) for 1 1/2 months and then released in Lake Michigan. During the spawning migration 18 months later, morpholine and p-alcohol were metered into separate streams, and the number of morpholine- and p-alcohol-exposed fish returning to each stream was determined. Seventeen other locations were also monitored. The majority of the fish exposed to morpholine were captured in the stream scented with morpholine and most fish exposed to p-alcohol were captured at the p-alcohol-treated stream. This field study demonstrates that coho salmon imprint to and utilize chemical cues for homing.

0f Wisconsin --Madison, Madi.issn, W153 706, USA HORRALL, R. M. 1981. Behavioral stock-isolating mechanisms in Great Lakes fishes with special reference to homing and site imprinting. Can. J. Fish. Aquat. Sci. 38: 1481 -1496.A moderately high degree of reproductive isolation is necessary for the formation and maintenance of discrete stocks of fish. This reproductive isolation can be developed through spawning site imprinting and homing -behavioral mechanisms that are apparently very * common in fish. During some part of their early life history, the fish become imprinted to, or conditioned to, environmental characteristics of the spawning site andlor to the pheromonal characteristics of their stock. At sexual maturity, they show an orientation-homing behavior back to the natal area where spawning then occurs reinitiating the cycle. Over time, stockspecific adaptations are made to the local environment which can involve changes in the morphologica1, physiological, or behavioral characteristics of the fish. Research on salmonids has provided the best evidence for site imprinting and natal homing in fish. Tagging and transplantation experiments with these species have been especially important sources of information. In coho salmon (Oncorhynchus kisutch), olfactory homing and olfactory site imprinting have been demonstrated by artificial imprinting techniques; it was found that the critical period for imprinting occurred during smoltification at an age of 15 or 16 mo. Most species do not undergo smelting, and imprinting occurs at a very early stage in the life history. It is hypothesized that the information which is imprinted about the natal site may be obtained from one or more of the following: odors in the water flowing over the site; odors originating from the site itself, and stock-specific pheromones emitted directly from the fish or from their waste products. Differences in characteristics of homing and imprinting in relation to the formation and maintenance of stocks are discussed for several Great Lake species including coho salmon. pink salmon (0. gorbuscha), lake trout (Salvelinus namaycush), white b a s (Morone chtysops), and walleye (Stizostedion vitreum vitreum). Inferences are made about how these characteristics relate to the rehabilitation of fish stocks in the Great Lakes and their tributaries. HORRALL, R. M. 1981. Behavioral stock-isolating mechanisms in Great Lakes fishes with special reference to homing and site imprinting. Can. J. Fish. Aquat. Sci. 38: 1481 -1496.Pour que des stocks de poissons distincts se foment et se maintiennent, il faut un certain degri d'isolation reproductrice. Gette isolation p u t se divelopper par imprignatipn du site de psnte et homing -micanismes apparemment tres communs chez les poissons. A un stade quelconque du d6but de leur cycle biologique, les pissons deviennent imprignis ou conditionnis par les caractiristiques ambiantes du site de ponte et (ou) aux caracteristiques phiromonales de l e u stock. Quand ils atteignent la maturite sexuelle, ils snt un comprtemen...

Individual courses, obtained by ultrasonic tracking nine sockeye in 1969 and nine in 1970, ranged up to 130.8 km (24.2 median) and 66.6 hr (9.6 median). Course directions were mainly to the north and west in 1969 and to the south and east in 1970. This difference may have arisen from differences in home river affiliation of the tracked sockeye. Swimming speeds showed a pronounced diel rhythm with higher values at 1400 hr and lower values at 0200 hr. The average speed of 53 cm/sec was consistent with rate of movement estimates obtained previously from tagging–recapture studies. A 13 cm/sec greater average speed in 1970 than in 1969 was observed, and possible reasons for the difference were discussed. Differences in speed within or beyond 2 km from land were not observed for either year. A diel rhythm in the magnitude of course change appeared, with a decrease in the frequency of large angular changes occurring in the afternoon. An orientation mechanism involving a daily reorientation process is hypothesized.