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

Self-sustaining populations of chinook salmon (Oncorhynchus tshawytscha) we re established in New Zealand, from a common introduction group, near the t urn of the 20th century. To investigate possible population divergence over this relatively short time scale we compared size, growth, and hypersalini ty tolerance of families from two populations over their first year of rear ing under shared conditions. Differences in initial fry mass were consisten t with egg-size differences, but there was also evidence of genetic differe nces in early growth rates. Size differences between the populations decrea sed over time and rank correlations of mean family mass with initial egg an d fry masses degraded over increasing intervals to nearly zero by the end o f the year. Population effects on hypersalinity tolerance were not apparent after 4, 6, or 10 months of rearing (from yolk absorption), but family eff ects were suggested by ANOVAs and by the existence of groups of families wi th seemingly different relative seasonal optima for tolerance. Thus far, in vestigation of juvenile traits under common environmental conditions has sh own 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.