Gulf Stream (Fla.)

The mechanisms of larval fish transport have been rigorously studied in the past several decades, building foundational knowledge of key biological and environmental factors with which to inform decisions about species management. This study has been built upon information gained from previous studies to further elucidate the processes involved at the recruitment stage of larval fishes. Vertical swimming behaviors of larval fishes enable deliberate orientation within the water column to allow organisms of limited mobility greater control over their horizontal movements. Vertical accumulation patterns of larvae are found to be tightly dependent on the strength of stratification within the water column at nursery entrances, such as estuaries. Onshore currents, such as upwelling and surface intrusions, are found to be conduits for entry into these systems. This study observed and analyzed the influence of intrusions by the Gulf Stream into the Fort Pierce Inlet and the vertical accumulation patterns of late-stage larvae associated with those events. This study incorporated a well-established zooplanktonic abundance sampling technique to achieve two primary goals: (1) to analyze the vertical abundances of larval fishes in stratified flow during Gulf Stream intrusions and (2) to assess the correlation between larval influx and intrusion events. The results of this study show a significant and positive correlation between propagule pressure of larval fishes and incidence of Gulf Stream intrusion events. Whereas previous studies have primarily described the spatiotemporal aspects of larval transport in a broader sense, our findings revealed a greater layer of complexity in the mechanisms of transport by incorporating localized hydrographic features. The information gleaned from these results can inform the ecological considerations of future fisheries management and study efforts via additional understanding about the role of physical oceanographic events in a critical life stage.

The Gulf Stream current in the Straits is typically dominated by a strong northerly current,
associated shear, and eddies. The water column also includes a prominent thermocline and
periodically features internal waves centered on the upper or lower edges of the thermocline.
Despite numerous previous related studies, there is limited available field data on internal waves
in the Straits of Florida. Here, study and analysis of velocity, temperature and conductivity data
acquired in the Straits over a period of time are described, in support of identifying presence of
internal waves in the flow. A systematic procedure is employed in modifying the universal Garrett-
Munk spectrum for internal waves in the open ocean for application to flow in the Straits of
Florida. Using this process, identified internal waves are characterized and related velocity
fluctuations in the time series are isolated to facilitate consideration of their correlations with
simultaneously observed magnetic fields.