Juvenile and Adult Striped Bass Mortality and Distribution in an Unrecovered Coastal Population

Striped Bass Morone saxatilis fisheries have been important in the eastern United States since the 1700s, but many populations have declined from historic levels. Enhancement programs, harvest reduction, water quality improvements, and habitat restoration have led to successful recoveries for specific stocks. However, these efforts have not been successful for the Striped Bass population in the Neuse River of North Carolina. Possible mechanisms inhibiting recovery of this population include overharvest, high discard mortality, poor water quality, and altered flow regimes. These mechanisms and their impacts on the Neuse River population are unclear; therefore, to gain insight, we estimated mortality and distribution of the population. Specifically, we tagged 100 hatchery-reared phase II juveniles (202-227mm TL) and 111 resident adults (349-923mm TL) with acoustic transmitters (a subset of 50 adults was also tagged with external high-reward tags). We used telemetry to monitor movement and seasonal distribution from December 2013 until September 2015. Telemetry and tag reporting data informed mortality models, and we estimated that annual discrete total mortality of phase II stocked juveniles was 66.3% (95% credible interval [CI]=47.4-82.4%). Annual discrete total mortality of adults was 54.0% (95% CI=41.5-65.4%). Adult discrete natural mortality was 20.1% (95% CI=8.7-39.1%), and neither juvenile nor adult natural mortality was correlated with seasonal variation in dissolved oxygen, temperature, or salinity. These results show that poststocking mortality is significant and that juvenile mortality should be considered when establishing stocking goals. Additionally, adult natural mortality is within the range predicted by maximum age and by previous studies; however, adult total mortality is higher than targeted rates. These results can help to inform management decisions and develop measures to rebuild depressed Striped Bass populations like that in the Neuse River.