INFLUENCE OF TEMPERATURE ON INCUBATION RATES OF COHO SALMON (ONCORHYNCHUS-KISUTCH) FROM 10 WASHINGTON POPULATIONS

Coho salmon embryos from 10 Washington populations were incubated unde r controlled conditions to determine the levels of variation in time t o hatch among populations and families within populations. The average incubation rate was somewhat slower than that estimated from a quanti tative model derived from British Columbia populations, and was slight ly faster than that predicted by a Washington model. Significant varia tion in incubation rates among the Washington populations was detected , consistent with results from other studies. Dates of first hatching of families within populations ranged more than two weeks at 6 degrees C. Within families, the first and last individuals to hatch ranged ov er 1-3 weeks. The variation in incubation rate among populations likel y reflects local adaptation to the thermal regimes of the rivers. The variation within populations and families will contribute to the varia tion in emergence date of fry, which will affect their growth and surv ival.