Florida waters, although there is 

 distinct temperature amplification. 

 Jones et al. (1970) and Roessler et 

 al. (1969) report notable spawning 

 peaks occurring in spring and summer 

 which apparently depend on bottom 

 water temperatures. The temperature 

 regime is fairly constant all year 

 in the Tortugas grounds, although 

 Iversen and Idyll (1960) note that a 

 thermocline may develop during the 

 summer. This is generally a short 

 lived phenomenon, however, due to 

 the influence of strong winds. The 

 occurrence of an occasional thermo- 

 cline may help to explain the spora- 

 dic nature of summer spawning peaks 

 noted by Roessler et al. (1969). 

 Shrimp spawn most actively between 

 27° and 30.8°C (81° and 87° F). 



Spawning is generally restric- 

 ted to areas greater than 6 fathoms 

 (39.4 m or 129 ft) in depth. There 

 is also some indication that spawn- 

 ing is greater during the waning 

 moon phases. An average annual 

 production of 87 x 10" protozoea/ 

 year is estimated by Roessler et al. 

 (1969). Average survival rates 



ranging from 74% to 98% percent 

 (mean = 80.4%) per day are estimated 

 for larval stages of pink shrimp 

 (Munro et al. 1968, Jones et al. 

 1969, Roessler et al. 1969). 



Early nauplii and young proto- 

 zoeal stages are believed to remain 

 fairly close to the bottom. How- 

 ever, second and third protozoea and 

 mysis stages apparently undertake 

 considerable vertical migrations, a 

 behavior that may greatly enhance 

 their ability to exploit prevailing 

 surface and bottom water movements 

 and thus move in a net direction. 



In the simplified model of 

 Figure 59, larvae are portrayed as 

 following two routes in their quest 

 to reach estuarine nursery areas. 

 The first, and lesser studied route. 



Figure 59. Simplified model of 



shrimp migratory patterns 

 in south Florida (adapted 

 from Ingle et al. 1959) 



involves direct travel across the 

 shallow shelf toward the Ten Thou- 

 sand Islands, Whitewater Bay, and 

 Florida Bay. In taking this route, 

 planktonic larvae must traverse an 

 area of very complex and sometimes 

 contrary currents (see Florida Keys 

 Hydrology, Section 5.7). Nonethe- 

 less, Jones et al. (1969) reported 

 finding numerous post larvae appar- 

 ently moving in this direction. 

 The second route is somewhat less 

 direct, but probably more energy 

 efficient for the larvae. It invol- 

 ves the fortuitous coupling of the 

 planktonic life style with locally 

 cycling currents. In this route 



larvae are swept southwestward by 

 prevailing surface and bottom cur- 

 rents. Further south, as these cur- 

 rents become increasingly influenced 

 by the Florida Current, the larvae 

 are swept northeastward along the 

 outer banks of the coral reef tract. 

 As the shrimp larvae gradually move 

 northeastward they develop into post 

 larvae. By the time developing 



203 



