Growth and salinity tolerance of juvenile chinook salmon (Oncorhynchus tshawytscha) from two introduced New Zealand populations

Abstract

Self-sustaining populations of chinook salmon (Oncorhynchus tshawytscha) were established in New Zealand, from a common introduction group, near the turn of the 20th century. To investigate possible population divergence over this relatively short time scale we compared size, growth, and hypersalinity tolerance of families from two populations over their first year of rearing under shared conditions. Differences in initial fry mass were consistent with egg-size differences, but there was also evidence of genetic differences in early growth rates. Size differences between the populations decreased over time and rank correlations of mean family mass with initial egg and fry masses degraded over increasing intervals to nearly zero by the end of the year. Population effects on hypersalinity tolerance were not apparent after 4, 6, or 10 months of rearing (from yolk absorption), but family effects were suggested by ANOVAs and by the existence of groups of families with seemingly different relative seasonal optima for tolerance. Thus far, investigation of juvenile traits under common environmental conditions has shown less genetic divergence between the two New Zealand populations than is suggested by the range of differences found for phenotypic traits measured on wild adults in previous investigations.