Site Selection and Time of Spawning by Two Groups of Kokanee in Odell Lake, Oregon

Abstract

The time and area of spawning of two groups of kokanee (Oncorhynchus nerka) in Odell Lake, Oregon, were observed in the fall of 1965. The first group was from the 1963 hatchery release (Kootenay Lake, British Columbia stock). They spawned from mid-September until early November in the outlet stream, the main tributary, and along one section of the lake shore. The second group, comprised of the natural-reared kokanee of the lake, spawned from early December until mid-January, apparently along only one section of the lake shore. In addition, females of the two groups were significantly different (P < 0.05) in mean length and mean weight. The regressions of egg number on fork length showed no significant difference. Reasons for the selection of spawning sites and the origin of the stock of the second group are suggested. Odell Lake in the central Cascade Range of Oregon contains an important fishery for kokanee. The lake lies at an elevation of 4,792 ft, covers 3,593 surface acres, and has a maximum depth of 282 ft (Fig. 1). It is fed by two major tributaries, Trapper and Crystal creeks. Odell Creek, the outlet stream, drains the lake and flows 13 stream miles before entering Davis Lake. Trapper and Crystal creeks receive snow melt from higher elevations. Underwater springs are present along the shoreline near the Post Office Lodge. Since 1950 the Oregon Game Commission has stocked the lake annually with 100,000 to 500,000 kokanee fry and fingerlings. It had been assumed that the fishery was being maintained by the annual stockings but creel census conducted on the fishery in 1964 and 1965 revealed that only 27 and 23 percent of the kokanee catch were of hatchery origin (Campbell 1965, Averett 1966). A study was initiated in the fall of 1965 to determine the location and magnitude of natural spawning. Two distinct spawning groups were subsequently discovered. The first group, primarily of hatchery origin, spawned in two streams and on the lake shore in September and October. The second spawned in December and January along the lake shore only and was composed of kokanee. The term wild in this report refers to kokanee hatched in Odell Lake. Sources of eggs for the hatchery fish released in Odell Lake have been Kootenay Lake, British Columbia (Meadow Creek strain), and Flathead Lake, Montana. Kokanee were introduced into Odell Lake before 1950 but the source of eggs and year of initial stocking are not known. All fish stocked between 1962 and 1965 were from Kootenay Lake. Kokanee from Flathead Lake were stocked several times before 1962 and again in 1966. Since 1962, portions of the hatchery fish have been marked by fin removal to assess the hatchery contribution to the sport fishery. The purpose of this paper is to show the differences in time of spawning and site selection between the natural-reared and hatchery introduced kokanee of Odell Lake. We wish to thank A. J. Tolmsoff, now at the University of Missouri, for assisting in 1 Contribution from Dingell-Johnson Project F71-R, Oregon. 2 Present address: Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. 3 Present address: Department of Biology, Nevada Southern University, Las Vegas, Nevada.