Data from: Multiple spawning run behavior and population consequences in migratory striped bass Morone saxatilis

Multiple spawning runs cause different contingents within the same population to experience varying demographic fates that can stabilize populations through the portfolio effect. Multiple spawning runs are reported here for the first time for striped bass, an economically important coastal species, which is well known for plastic estuarine and shelf migration behaviors. Adult Hudson River Estuary striped bass (n=66) were tagged and tracked with acoustic transmitters from two known spawning reaches separated by 90 km. Biotelemetry recaptures for two years demonstrated that each reach was associated with separate spawning runs. Time series of spawning run trajectories were examined via nonparametric dynamic time warping and revealed two dominant time series centroids, each associated with the two spawning reaches. In 2017, the lower reach run occurred earlier than the higher reach run, but difference in timing was not observed in 2018. The majority (84%) of returning adults in 2018 showed the same run behaviors exhibited in 2017. The two spawning run may have been cued differently by temperatures, where warming lagged 1-week at the higher reach in comparison to the lower reach. The two spawning runs exhibited similar Atlantic shelf migration patterns with strong summer fidelity to Massachusetts Bay and winter migrations to the southern US Mid-Atlantic Bight. Still, in 2017, differing times of departure from spawning reaches into nearby shelf waters likely caused the early spawning run to experience substantially higher mortality than the later run. Anecdotal evidence suggests that higher fishing effort is exerted on the early-spawning run as it first enters shelf fisheries. Thus, as in salmon, multiple spawning runs by striped bass can lead to differential demographic outcomes, contributing to overall population dynamics.