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Morphological heterogeneity of kokanee, "oncorhynchus nerka kennerlyi" (Suckley), in Kootenay Lake, British Columbia Vernon, Edwin Herman

Abstract

Samples of kokanee drawn from the spawning runs to seven streams tributary to Kootenay Lake, British Columbia, were compared statistically for morphometric variation between streams, between areas in the lake and between years. Kokanee within three arbitrarily delineated areas displayed great similarity in age, size, vertebral count, scale pattern and development of secondary sexual characteristics. Samples from a representative stream of each area differed significantly in age at maturity, size, growth rate in the first year, vertebral count, scale row count, gill raker count, head length of males, growth form of caudal peduncle, eye diameter, development of secondary sexual characteristics, ova per unit total weight and commencement of spawning period. Some significant variation in size and vertebral count of samples from each area occurred between years but this did not obscure the significance of variation between areas in any one year. Differences in age, size, vertebral count and development of secondary sexual characteristics between areas persisted in all three years examined. Kokanee straying to spawn in areas other than their home area were identified by age, size, vertebral count, scale pattern and scale row count and these strays amounted to less than three percent of 1137 specimens examined. The strong tendency of kokanee to home their parent stream is considered of prime importance in the establishment and continued existence of three partially isolated but occasionally interbreeding populations in Kootenay Lake. The morphometric heterogeneity of kokanee in Kootenay Lake is most probably a result of phenotypic variation. Some genotypic morphological variation may have occurred but the interbreeding between populations is probably sufficient to preclude sympatric speciation.

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