

A\ 



\ i 



i if- -\ 



/A V A \ 



1 1967 



NEW MOON PERIOD 



Figure 60. Seasonal abundance of 

 post larval shrimp at 

 Whale Harbor Channel 

 in the upper Keys 

 (adapted from Allen 

 et al. 1980). 



shrimp reach the post larval stage 

 they begin to enter Florida Bay on 

 incoming tides through the channels 

 in between the Keys (Allen et al. 

 1980). Figure 60 displays the obvi- 

 ous correlation between sea water 

 temperature and post larval abun- 

 dance in one such channel in the 

 upper Keys. Seasonal peaks in 



abundance occur from May through 

 August or September. Superimposed 

 on this pattern Allen et al. (1980) 

 also report seasonal variation in 

 the depth at which shrimp post lar- 

 vae abound (Table 42). During peak 

 seasonal abundance the shrimp tend 

 to concentrate in the surface wa- 

 ters, while during lower periods of 

 abundance highest numbers are found 

 at mid-depth. 



Apparently one of the more 

 important factors controlling the 

 migration of shrimp is their ability 

 to respond differently to ambient 

 conditions as a function of life 

 stage. The post larvae, which are 

 looking to enter the nursery area, 

 seem to seek out the incoming tides 



Surface 

 Mid depth 

 Bottom 



Percent by Season 



Overall May-Aug. Sept. -April 



39.9 33.1 59.7 



54. 7 60.9 36.9 



5.4 6.0 3.5 



Table 42. Seasonal variation in the 

 relative distribution of 

 pink shrimp post larvae 

 with depth (adapted from 

 Allen et al. 1980). 



and avoid the outgoing tides (Allen 

 et al. 1980). The reverse is appar- 

 ently the case for juvenile shrimp 

 on their way back offshore (Tabb 

 et al. 1962). 



A number of authors have point- 

 ed to the seasonal correlation be- 

 tween nearshore salinity and runoff, 

 and post larval and juvenile shrimp 

 abundance. Allen et al. (1980) 



believe the increased intertidal 

 habitat created by seasonal water 

 level fluctuations in Florida Bay is 

 one of the more important factors 

 contributing to the survival of 

 young post larvae. Another factor 

 that must certainly be involved is 

 the tremendous seasonal pulse of 

 detritus in the nearshore ecosystem. 

 Still another reason may be the 

 relative protection from aquatic 

 predators afforded by the low sa- 

 linity environment. Whatever the 

 nature of the dependence may be, the 

 estuarine and nearshore Keys envi- 

 ronments most definitely play a key 

 role in the productivity of the 

 Tortugas shrimping grounds. 



While in the Florida Bay nur- 

 sery area, there appears to be 

 an increasing gradient of size 

 and age toward the north (Allen et 

 al. 1980), indicating a gradual 



204 



