Empirical Review of Coho Salmon Smolt Abundance and the Prediction of Smolt Production at the Regional Level

Abstract

Regional habitat and fisheries management planning requires estimates of the capacity of watersheds to produce salmonids. To predict the average abundance of smolts of coho salmon Oncorhynchus kisutch produced by streams and rivers, we related estimates of smolt abundance to habitat features derived from maps and discharge records. We assembled a database of 474 annual estimates of smolt abundance from 86 streams in western North America for this analysis. We found that only stream length and to a lesser extent latitude were useful in predicting mean smolt abundance. The frequency distribution of annual estimates of smolt abundance from individual streams tended towards a normal rather than the more usual lognormal distribution; the median coefficient of variation in abundance was 37%. Our results are consistent with the view that, on average, smolt abundance is limited by spatial habitat, but that there is significant annual variation in abundance probably due to variation in habitat quality caused by climate, flow, or other factors. We conclude that forecasting smoll yield from stream length and latitude is feasible at the watershed or regional level, but that the precision of a prediction for a single stream is poor. A more detailed approach will be required for local forecasting.

Proceedings of the coast redwood forests in a changing California: A symposium for scientists and managers

“…This information suggests that the characteristics of coho size at outmigration are variable by watershed. Coho forklengths were comparable to the size range reported by Bradford et al (1997) throughout Oregon and Washington.…”

Effects of subsidies from spawning chum and pink salmon on juvenile coho salmon body size and migration timing

“…A consistent relationship between spawning and juvenile coho salmon has not been established. It is thought rather that juvenile coho salmon production is regulated by the availability of rearing habitat in the stream, unless spawning coho salmon densities are very low (Bradford et al 1997). The number of spawning pink and chum salmon far exceeded the number of spawning coho salmon at the five streams with count data available for all three species (mean 3611, 1138 and 138 females/km for pink, chum and coho, respectively) and during visual observations during spawning at all of the streams in this study.…”

Valuing freshwater salmon habitat on the west coast of Canada

“…In studies of coho smolt production in the coastal area of BC (Bradford et al, 1997), some production rates are higher. To assess the impact of underestimating the smolt production rate in the South Thompson on our results, we carried out an additional sensitivity calculation.…”