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Patterns of animal migration often vary dramatically within species. Understanding the mechanisms, which shape this variation, is important due to the powerful impacts migratory species can have upon ecosystem processes. Migratory timing is thought to be especially critical for survival and reproductive success and variance in migratory timing has been shown to differ between individuals and seasons across a wide range of taxa. Here we investigate the ecological and evolutionary mechanisms, which drive this commonly observed phenomenon. By individual based tracking of roach, a common migratory freshwater fish, in European lakes over multiple migration periods we obtained highly detailed (year-round scheduling and repeat journeys) information on the migratory patterns of both populations and individuals. Our analyses show that individuals exhibit strong site fidelity and consistency in timing if migration. Furthermore, variation in migratory timing differed seasonally with less variance and more pronounced migration synchrony in spring as compared to autumn. We then show that at an individual level, survival is strongly linked with the timing of spring migration, but not to autumn migration. Hence, natural selection acts to reduce variance in spring migratory timing via survival costs to individuals that deviate from an optimal migratory schedule in spring but not autumn. Our data provides a detailed insight from a longitudinally monitored, wild population into intrapopulation variability in migration strategies and fitness correlates of individual variation in migratory timing.