45 



- N=225 



40 



35 



s 



25 



20 



I5fc 







• J 



_I I I I I I L. 



9 10 



15 20 



DEPTH (FMJ 



25 



45 



40 



35 



-I 30 



S25 

 ui 



s 



: MALES ■ X (Y=I6.394 + 0.618X) 

 FEMALES • e {Y-^ 17.914 +0.868X) 

 MALES AND FEMALES'* (Y-^ 17.307 -(-0.739X) 



20- 



I5tj_ 



-I I I 



_l L. 



9 10 



15 20 



DEPTH (FM.) 



25 



Figure 8.— Relationship of depth of water and average size of Figure 9. — Relationship of the annual average size of shrimp 

 male shrimp. and depth of water. 



there is a considerable range of sizes 

 at all depths. Some important causes of 

 this variation will be discussed in sub- 

 sequent sections. 



The following figures (10 to 13) contain 

 data gathered on groups of cruises and 

 these points should be noted: 



1. The average size (carapace length) 

 of shrimp on the grounds. 



2. The distance between isopleths. 

 When the standard isopleths are close 

 together, the average size of shrimp is 

 changing rapidly and conversely. 



3. Direction of the gradient. When 

 the isopleths are parallel over some dis- 

 tance on the grounds, a positive gradient 

 exists. 



Examination of these isopleths shows, 

 with minor exceptions, that two patterns 

 of size distribution predominate on the 

 Tortugas grounds. One is the increased 

 size with depth and the other a size 

 gradient in a northerly direction irre- 

 spective of depth. Without complete cov- 

 erage of the fishing grounds during each 

 cruise, a complete evaluation of the sig- 

 nificance of these two patterns is not 

 feasible. We have shown in figures 7, 

 8, and 9 that a size -depth relation exists 

 but we must consider that such a rela- 

 tionship may be a function of diffusion 

 or dispersion of individuals from the 

 Keys. Considering the number of cruises 

 in which the resultant isopleth lines cross 

 fathom contours, we strongly entertain 

 this possibility. 



These data suggest that small shrimp 

 move onto the grounds from the east 

 and southeast and increase in size as 



11 



