Expanded, compressed, or equal? Interactions between spawning window and stream thermal regime generate three responses in modeled juvenile emergence for Pacific salmon

Climate warming poses challenges to native fish, particularly at high latitudes. We used incubation models to explore how interactions between spawning timing and daily varying water temperature affected emergence timing for five species of Pacific salmon in 33 thermally diverse streams in south-central Alaska. Interactions between spawning timing and stream thermal regime led to three different emergence timing responses: (1) "expanded" by typically 2-3 times the duration of the spawning window for summer spawning salmon at streams with a large annual water temperature range; (2) "equal" in duration to the spawning window, regardless of spawning timing, at streams with upwelling groundwater; and (3) "compressed" for late -spawning salmon where water temperature was cooler at spawning than at emergence. Across all sites, a +/- 15 -day range in spawning timing had influence similar to anomalously warm winters (+2 degrees C to +3 degrees C) on the emergence timing window. Differences among species, spawning timing, and thermal regimes suggest that a range of adaptations in spawning behavior will likely enable Pacific salmon populations to accommodate shifting thermal regimes during their early life history.