Communications: Life Histories and Precocity of Chinook Salmon in the Mid-Columbia River

We review available information on the phenomenon of precocious sexual development in stream-type (spring run) male chinook salmon (Oncorhynchus tshawytscha), provide some new data, and suggest implications. Females consistently outnumber males about 3:2 in adult returns of stream-type chinook salmon to the mid-Columbia River. No selective harvest occurs. Sex ratios of juveniles favor males. Precocious parr experience more deaths than nonmaturing juveniles, which leads to more females than males among returnees from the ocean. Precocious maturation of males is characteristic of both hatchery and wild stocks. Rapid growth in hatcheries may result in a large increase in precocious males. This could be one factor in the low survival (0.16–0.55%) of stream-type chinook salmon from mid-Columbia River hatcheries.