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.

Striped bass egg densities were digitized from tables or figures of multiple years' "Year Class Report for the Hudson River Estuary Monitoring Program".  Provided number of eggs/1000 m³ were summed across the months of May and June for each Hudson River region. Citations of individual reports are found in:

Applied Science Associates I. 2014 Year Class Report for the Hudson River Estuary Monitoring Program. Prepared for Entergy Nuclear Indian Point 2 L.L.C., Entergy Nuclear Indian Point 3 L.L.C., and Entergy Nuclear Operations, Inc. 2016.

Fish biotelemetry detections were collected by receivers deployed and maintained by the authors, as well as through data sharing agreements with members of the Atlantic Cooperative Telemetry Network and the Mid-Atlantic Acoustic Telemetry Observing System.

Hudson River water quality data were downloaded from the USGS National Water Information System, Station 01372058.

Time series of striped bass spawning runs was created by using the mean daily latitude of each fish. Values between 4 April and two days before the first recorded detection within the Hudson River, as well as values between two days after the last recorded detection within the Hudson River and 26 June were given the value of 41°N. All remaining missing values were imputed with a 4 day exponential moving average.

Characterization of the spawning runs of 2017 and 2018 was conducted via k-medioids partitional clustering using dynamic time warping as a similarity measure, and is the subject of the manuscript in progress.

Refer to README.txt.