Morphometric Comparison of Three Races of Kokanee (Oncorhynchus nerka) Within a Large British Columbia Lake

Abstract

Samples of kokanee (land-locked sockeye salmon) drawn from the spawning runs to seven streams tributary to Kootenay Lake, British Columbia, were compared statistically for morphological variation between streams, between lake areas and between years. Kokanee within three major lake areas displayed great similarity in age, size, vertebral count, scale characters and development of secondary sex characters. Samples from a representative stream of each area differed 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 sex characters, ova per unit total weight, and commencement of spawning period. Variation between years in size and vertebral count did not obscure or alter the stability of differences between races over a period of four years. Kokanee straying to spawn in areas not of their natal origin were identified by age, size, vertebral count, scale character, and scale row count, and totalled less than three per cent of 1,131 examined. Progeny of parents from the three races were propagated in a uniform environment from fertilization to six months after hatching. Parental differences in number of vertebrae were transmitted to offspring. Segregation during reproduction, due to strong homing tendencies, is considered the principal isolating mechanism leading to some genotypic divergence and considerable phenotypic variability.