The velocities of the resultant tidal and wind-driven currents are 

 small and apparently are not sufficient to account for transport of shrimp 

 larvae from the offshore spawning grounds to mainland nursery areas. The 

 density currents are of higher velocity but generally occur west of the prin- 

 cipal spawning area. In August and September 1961, however, a southwest- 

 erly density current was observed on the spawning grounds. 



The spawning season of pink shrimp, as indicated by the presence 

 of young stages in the plankton, extends throughout the year. A seasonal peak 

 in spawning occurs in spring or sunruner and generally is associated with ris- 

 ing water temperatures. In I960, a seasonal peak in spawning occurred in 

 nnidsummer. In 1961, the spawning peak was in the spring. It was followed 

 by low spawning intensity during the sumnaer, associated with low tempera- 

 ture of the bottom water over much of the spawning area. 



The average age of pink shrimp in the plankton increased from 5. 5 

 days at the western edge of the spawning area to 29. 7 days near the mainland. 

 This increase suggests a movement from the spawning area across the Tor- 

 tugas Shelf towards the mainland but does not exclude the possibility that 

 planktonic stages nnay also move toward the Florida Keys. Shrimp of greatest 

 average age were taken off the principal entrances to the Whitewater Bay es- 

 tuary, which is known to be a nursery area for the Tortugas pink shrinap. 

 Since resultant currents of the Tortugas Shelf do not move in an easterly di- 

 rection, it is apparent that at least the older planktonic stages do not freely 

 drift in the water mass but either actively swim across the Shelf towards 

 shallow water or take advantage of the east-west movement of tidal currents. 



94 



