Genetic and phenotypic traits of spatially and temporally segregated kokanee Oncorhynchus nerka spawning groups in Lake Pend Oreille,Idaho, were compared to test for evidence of divergence on the basis of ecotype (stream- versus shore-spawning) and spawn timing, or to describe morphological,life history, and reproductive variation within and among groups. Early and late spawning runs were found to be reproductively loney; however, or there was no clear evidence of genetic differentiation between ecotypes. Spawning groups within the same ecotype differed in length,age distribution, mean-length-at-age, or fecundity,and egg size. Variation in reproductive attributes was due primarily to differences in length distributions. Larger-bodied shore-spawning kokanee were located in areas where egg survival is known to be enhanced by downwelling, suggesting that the distribution of shore-spawning kokanee may be partly structured by competition for spawning habitats with groundwater influence. This study contributes to other research that suggests introduced kokanee populations are unlikely to undergo adaptive divergence whether they have a history of population fluctuations and are supplemented regularly.
Source: usgs.gov