Sex-specific reproductive investment and survival of adult Atlantic salmon kelts across multiple dams

In adult Atlantic salmon, individual variation in migration and movement within rivers during spawning (i.e., reproductive movement, RM) is an important component of overall reproductive investment that may influence subsequent survival and repeat spawning. We test the cost-of-reproduction hypothesis—which states that increased reproductive investment decreases survival—by first quantifying individual RM of landlocked Atlantic salmon and then evaluating how RM, sex, and dams influence outmigration survival. Consistent with sexual selection for male mobility, male RM was ~4 times greater than that of females: they moved further, were more exploratory, visited a tributary more, went further upstream, and spent longer in the river. Results provide mixed support for a cost of RM on outmigration survival: individuals (inclusive of both sexes) that abandoned spawning and migrated downstream (i.e., “fallbacks”) survived 3.5-fold better than those that spawned (supporting an overall cost-of reproduction). However, males (with higher RM) had 2.8 times higher survival than females, and among males there was no effect of RM on survival (not-supporting a cost-of-RM). The most influential factor on survival was dam interactions, which reduced per-kilometer survival 18-fold relative to migration within free-flowing reaches. Documenting male-biased survival was unexpected given the (1) high RM of males and (2) that most prior studies find higher outmigration survival of female Atlantic salmon. We highlight how dams exacerbate the already high costs of reproduction in Atlantic salmon, which has important implications for contemporary evolution of behavioral tradeoffs.