Divergence in juvenile growth and life history in two recently colonized and partially isolated chinook salmon populations

In 47 families of New Zealand chinook salmon, Oncorhynchus tshawytscha deri ved from two populations, differing ih mean spawning date by 11-17 days and in juvenile life history, neither mean ovum weight nor mean time to hatch differed between the two populations, but substantial differences in mean f amily weight were apparent from 6 months after fertilization. Differences i n growth rates from 12 to 24 months were relatively small, suggesting that most of the divergence in size and growth occurred during the first 6 month s of life. There were differences in mean weight for families spawned 11-17 days apart, the approximate interval by which peak spawning date differs b etween the two populations, but these did not persist beyond 7 months. Diff erences between the two populations are consistent with their natural life history. The slower growing population experiences cooler temperatures duri ng stream residence and is dominated by fish which spend a year in flesh wa ter before seaward migration, whereas the faster growing population normall y experiences warmer temperatures and migrates to sea in the first year of life. These results provide further evidence of life history evolution in p artially isolated chinook salmon populations within 90 years (c. 30 generat ions) of becoming established. (C) 2000 The Fisheries Society of the Britis h Isles.