Lake Trout Reproductive Behavior :

Chemosensory cues, particularly those emanating from substrate areas occupied by previously hatched young, may play an important role in the reproductive behavior of lake trout Salvelinus namaycush. Support for this hypothesis was obtained in laboratory experiments. Adults were placed in a large circular pool with four experimental reefs. Egg membranes and feces obtained from young that had hatched earlier were placed in polyester fiber in screen envelopes and positioned on selected reefs. Females approached and males contacted ("cleaned") the treated reefs but not the untreated reefs. Of 6,858 eggs recovered, 92% were from treated reefs. Some of these eggs had been fertilized and provide the first record of volitional spawning by lake trout under artificial conditions. A second experiment was less definitive, because no spawning occurred, but visual observations and analysis of videotaped behavior sequences howed that, again, adults were attracted more to reefs treated with feces of young of the year than to untreated reefs. Received August 17, 1984 Accepted July 20, 1985 Highly productive native stocks of lake trout Salvelinus namaycush were severely depleted in Lake Superior and became extinct in the rest of the Great Lakes during the 1940s and 1950s due to predation by sea lamprey Petromyzon marinus and overfishing (Smith 1968). Although the sea lamprey is now largely under control, the goal of rebuilding self-sustaining populations of lake trout through stocking programs has not yet been achieved. Several hypotheses have been proposed to explain the poor natural reproduction by the stocked lake trout in lakes Michigan, Huron, and Ontario, where many millions have been planted (see reviews by Rybicki and Keller 1978; Martin and Olver 1980; Brown et al. 1981; Willford et al. 1981). Although many hatchery fish survive to maturity and appear to spawn at both traditional breeding grounds and artificial structures (Peck 1979, 1982), it is not clear how successful they are in locating areas with optimum conditions for survival of eggs and young (Brown et al. 1981; Horrall 1981; Foster 1984). Lake trout do not excavate a redd and typically spawn in the fall over cobble, rubble, boulders, or "honeycomb" rock with abundant interstitial spaces (Eschmeyer 1964; Martin and Olver 1980). 1 Contribution 649, Great Lakes Fishery Laboratory, U.S. Fish and Wildlife Service, Ann Arbor, Michigan 48105. Males usually begin aggregating at spawning areas a week or more before females arrive (Miller and Kennedy 1948; Cuerrier and Schultz 1957; Martin 1957; McCrimmon 1958; Eschmeyer 1964; DeRoche 1969). During tfie spawning period, the sex ratio on the breeding grounds is usually two to three males per female. In some populations, at least, males "clean" specific areas of the spawning substrate (Merriman 1935; Royce 1951; DeRoche and Bond 1957; Martin 1957; Foster 1984), defend breeding areas from egg predators (Merriman 1935), and make "threatening motions" at other males even though no vigorous fighting is observed (Royce 1951). Overall, the reproductive behavior of lake trout appears to fit the definition and criteria for lekking, characterized by temporary aggregation of sexually active males on a traditional breeding ground (lek) where courtship and spawning subsequently occur (Loiselle and Barlow 1979). No field observations of the lake trout's reproductive behavior in any of the Great Lakes have been published. In other populations, spawning usually begins near dusk and continues until about 2300 hours (Royce 1951; Martin 1957; Martin and Olver 1980). Such nocturnal spawning habits would favor the evolutionary development ofnonvisual (acoustical, near-field displacement, electrical, tactile, or chemosensory) cues for location of spawning sites and partners and for synchronization of gamete release.