Data from : Variation in salmon migration phenology bolsters population stability but is threatened by drought

Intrapopulation variation in movement is common in nature but its effects on population dynamics are poorly understood. Using movement data from 3,270 individually-marked fish representing nine cohorts of coho salmon (Oncorhynchus kisutch) in California, we show that bimodal intrapopulation variation in the timing of juvenile down-migration from their natal habitat and subsequent residence in non-natal habitat affects growth, emigration timing, and the abundance and stability of adult returns. Non-natal rearers (early down-migrants) exhibited more variable growth and more variable but earlier emigration to the estuary than natal rearers (late down-migrants). While natal rearing was more common, non-natal rearers were overrepresented among adult returns, and non-natal returns were 1.6 times more stable than natal returns. Our results demonstrate that variation in migratory behavior bolsters population stability through portfolio effects. However, non-natal rearing is reduced in low water years, suggesting that drought exacerbates population instability by reducing critical intrapopulation variation.