Effects of Logging on Stream Temperatures in Carnation Creek British Columbia, and Associated Impacts on the Coho Salmon (Oncorhynchus kisutch)

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Abstract
Clear-cut logging of 41% of the basin of Carnation Creek, British Columbia, resulted in increased stream temperatures in all months of the year. Increases above prelogging temperatures ranged from 0.7.degree. C in December to 3.2.degree. C in August. Earlier emergence of coho salmon (Oncorhynchus kisutch) fry associated with the temperature increases lengthened their summer growing season by up to 6 wk. Fingerlings were significantly larger by the fall in the years after logging compared with the years before logging. The increased size of fingerlings was associated with improved overwinter survival. Following logging, yearling smolt numbers double, although 2-yr-old smolt numbers decreased. Warmer spring temperatures were also associated with earlier seaward migration of smolts, probably resulting in decreased smolt-to adult survivals. A linked series of models that first predict logging effects on stream temperatures and then the effects of those temperatures on critical coho life history events are developed. The life history model is used to quantify the effects of stream temperature changes related to logging on the population size of adult coho salmon. The predicted effect of those temperature changes was a 9% increase in adult coho numbers prior to the fishery, an increase considerably less than the observed 47% increase in smolt numbers.

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