An Approach to Estimating the Effects of High Temperature Exposure During Maternal Upstream Migration on Embryo Development and Survival in Chinook

Water temperature during upstream migration may directly affect migration behavior and survival, and potentially affect reproductive success indirectly by influencing gamete development and viability.  We examined the effects of high sub-lethal water temperature exposure on adult summer and fall Chinook salmon migrating in the Snake River basin. Investigations included comparison of adult thermal histories and embryo viability for female fish in relation to temperature exposure during migration.  Chinook salmon (n = 100) were tagged with radio transmitters and internally- and/or externally-mounted temperature recorders at Ice Harbor Dam in summer and fall, 2004.  Thermal histories recovered at hatcheries or Lower Granite Dam were used to study migration patterns related to water temperature.   Embryo viability tests were completed at Lyons Ferry and Nez Perce hatcheries for successful female migrants.

Fish were exposed to water temperatures as high as 23.6°C, and had total migration temperature exposures, recorded from Ice Harbor to Lower Granite Dam, as high as 19.2 degree days above 20°C and 60.0 degree days above 18°C. Migration temperature exposures were highly correlated with release date and the temperature at Ice Harbor Dam at the time of passage.

Embryo mortality was tracked for thirty fall Chinook salmon, and ranged from 1.1% to 19.8% (mean = 4.7%).  Embryo mortality data in relation to adult migration temperature exposures were available for 14 Chinook salmon, limiting statistical power. The five fish with the highest temperature exposures above 20°C (mean = 3.61 degree days) exhibited five of the six highest embryo mortalities at the eye-up stage and the button-up stage.  This represented a significant positive relationship between Chinook salmon embryo mortality and adult migration temperature exposure (P = 0.034).  A similar, but non-significant, relationship was observed when temperature exposures were calculated using an 18°C threshold. No relationship between temperature exposure and abnormalities was observed. The results demonstrate exposure to higher temperatures during upstream migration may negatively affect gamete development and the quantitative methods developed here provide a potential approach to estimating costs of migration through warmer environments predicted under climate warming.