released and recovered on the Tortugas grounds 

 (Iversen and Jones, 1961). Another offshore 

 release of stain-marked shrimp in Hawk Channel 

 (7), south of Bahia Honda Key, yielded recoveries 

 on the Tortugas grounds. 



Areal Distribution 



In figure 2 lines connecting release and recovery 

 sites suggest possible migration routes traversed 

 by pink shrimp en route to the Tortugas or 

 Sanibel grounds. Actual routes of migration are 

 not known because of the few recoveries in inter- 

 vening areas which receive limited fishing effort. 

 One exception pertains to the inshore leg of the 

 route followed by shrimp released near Bottle 

 Key as they moved toward the Tortugas grounds. 

 From this group, a bait shrimp fisherman re- 

 covered 10 marked shrimp in Florida Bay 22 to 80 

 days after release. Of these 10, 7 were found 

 near the release site, and 3 had moved southwest 

 of Bottle Key toward a pass breaching the Florida 

 Keys. Higman (1952) reported large catches of 

 shrimp at such passes on night tides flowing from 

 Florida Bay to the Atlantic Ocean. Undoubtedly, 

 many shrimp from Florida Bay move into Hawk 

 Channel, and we have now established that shrimp 

 from the Hawk Channel grounds south of Bahia 

 Honda Key migrate to the Tortugas grounds. 

 Such movement was suggested by Costello and 

 Allen (1960). 



The distribution of recoveries from individual 

 releases shows that migration routes may be broad 

 and that shrimp disperse considerably while mi- 

 grating. For example, shrimp released at Indian 

 Key have been recovered at points as far as 125 

 miles apart. When there is a protracted departure 

 time from a release site, such as occurred at Bottle 

 Key (table 1), separate elements of the marked 

 group may be subjected to a diverse environment 

 (temperature, salinity, tides, currents) that could 

 affect the direction of migration. 



On the Tortugas grounds, the size of pink shrimp 

 increases with the depth (Iversen, Jones, and Idyll, 

 1960). In general, mark-recovery experiments 

 also indicate that pink shrimp move into deeper 

 water as they increase in size. Thus, from exam- 

 ining the depth contours, we would expect that the 

 majority of recruits enter the Tortugas and Sani- 

 bel grounds from the shallower waters northeast, 

 east, or southeast of the grounds. On the Tortu- 

 gas grounds the recovery patterns of marked 



6uiF ^e- ; 



of r SW1IBEL 6«tOUM 



INC'liK IEIC " 



IE XIC0 



Figdre 3. — Distribution of recoveries of pink shrimp on the 

 Tortugas grounds from four release sites. 



shrimp from a common release area suggest the 

 directions from which the shrimp enter the 

 grounds. Reference is made to figure 3, which 

 illustrates the recovery positions on the Tortugas 

 grounds of shrimp liberated at four release sites 

 Because of varied fishing effort, the actual distribu- 

 tional pattern of marked individuals on the 

 grounds may differ somewhat from that suggested 

 by the recoveries. The greatest concentration of 

 fishing pressure occurs in the northeast quadrant of 

 the grounds followed, in descending order, by the 

 northwest, southwest, and southeast quadrants. 

 Fishing pressure in the southeast quadrant is 

 minimal and probably few recoveries should be 

 expected from there. Bearing these qualifications 

 in mind and by inspecting figures 2 and 3, we made 

 the following observations: 



1. Recoveries of shrimp migrating from the 

 Sanibel grounds (13) were confined to the north- 

 west quadrant of the Tortugas grounds, suggesting 

 entrance from the north. 



2. Recoveries of shrimp migrating from Indian 

 Key (14) were distributed within the northwest 

 and northeast quadrants of the Tortugas grounds, 

 indicating entrance from the north and northeast. 



3. Recovery positions of shrimp migrating 

 from Bottle Key (9) were concentrated in the 

 northeastern and west central portions of the 

 grounds. This recovery pattern may be dis- 

 torted by the limited fishing effort in the southeast 

 quadrant. Thus, indications are that Bottle 



MIGRATIONS OF FLORIDA PINK SHRIMP 



453 



