St. Johns River Morone Assessments

large school of fish underwater

Striped bass (Morone saxatilis) and hybrid striped bass (M. chrysops x M. saxatilis) have been stocked into the St. Johns River since the 1970’s. They can be found throughout the river in winter but high-water temperatures in the spring and summer force them to move into cool-water refuge such as Silver Glen Springs (SGS). FWC biologists use this annual concentration to gauge the abundance and health of the population via snorkel surveys. Typical summer utilization of SGS is above 1,000 Morones with fish health declining throughout their confinement. Outmigration seems to occur once river water temperatures drop below 25°C in the fall. In May 2018, a pilot telemetry study was initiated to determine the temporal and spatial movements of individual fish at SGS. Initial results suggest some level of movement in and out of SGS during summer residency, although as the summer progressed many fish left the system and never returned. While preliminary data may suggest high summer mortality and/or variable residence time, continued monitoring, along with an expansion in study area and a larger sample size in 2019 will help to fully assess these questions.