Water temperature, river discharge, and adult Sockeye salmon migration observations in the Meziadin watershed, 1966-2012 / by H.W. Stiff, K.D. Hyatt, M.M. Stockwell, S. Cox-Rogers, P. Hall, R. Alexander,... : Fs97-4/3019E-PDF

"Historical meteorological and hydrological data were assembled to review the influence of changes in these environmental factors on patterns of adult Sockeye migration in the Meziadin River, British Columbia. Regional air temperature data collected at Stewart, B.C. were statistically related to intermittent water temperature time-series (1999–2012) sampled at the Meziadin fishway to hind-cast daily water temperature in Meziadin River for 1910–2012. Surprise Creek daily discharge (1967–2010) provided the best predictor of historical Meziadin River flows, though these data could not replicate some observed Meziadin extremes. Frequency distributions of historical migration dates (1966–2012), weighted by the daily migration rate, were used to discern possible environmental thresholds defining high versus low migration classes. Peak-over-threshold analyses were applied to reconstructed time-series to review long-term trends in temperature and flow by site. The climatology remains cool in this northern watershed, with estimated daily mean water temperatures of 14.1°C (maximum 19.5°C) during Sockeye migration. Low daily migration rates (<1.25% of total escapement) were associated with water temperatures above 18°C. The average duration of “warm water” periods (>18°C) was <1–2 days for recent decades, and is not trending. While “low flow” events (Surprise Creek discharge <10th percentile of historic flows), which mainly occur after peak Sockeye migration, were not particularly associated with low daily migration rates, “high flows” (>90th percentile) were often associated with delayed migration, migration stoppages, and low daily migration rate. Migration rates were near-zero at high water temperature and high flow combinations. The frequency of high flow events increased in the 2000s relative to previous decades, along with the mean and maximum duration of high flow periods"--Abstract, page iv.

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