Key shrimp entered the Tortugas grounds from 

 the east, and, perhaps, northeast and southeast. 



4. Shrimp that migrated from Hawk Channel 

 (7) were concentrated along the southern border 

 and in the west central section of the Tortugas 

 grounds. Once again, the distributional pattern 

 may be distorted by limited fishing effort in the 

 southeast quadrant. It appears, however, that 

 Hawk Channel shrimp entered the grounds from 

 the southeast. 



On the south Sanibel grounds, distribution of 

 the first 23 recoveries of marked shrimp released 

 in Pine Island Sound indicates that these shrimp 

 entered the grounds from the shallower waters to 

 the northeast and east (fig. 4). A comparison 

 of the distributional pattern of the last 23 re- 

 coveries with that of the first 23 indicates the 

 general trend of movement was into deeper water, 

 or southwestward on the south Sanibel grounds. 



TIME DISTRIBUTION 



The period of tune expended by pink shrimp 

 (1) on nursery grounds, (2) while traversing mi- 

 gration routes, and (3) on the offshore grounds can 

 be approximated in some cases from the number 

 of days elapsing between release and recovery of 

 marked shrimp, or "days out time" (table 1). 

 Recovery frequencies for half-month periods on 



V = RELEASE DATE 



Figure 4. — Distribution of recoveries of pink shrimp on 

 Ilic south Sanibel grounds from releases in Pine Island 

 Sound. 



454 



Figure 5. — Time-frequency distribution of marked shrimp 

 recoveries on the Tortugas and Sanibel grounds by one- 

 half-month periods. 



the Tortugas and Sanibel grounds (fig. 5) indicate 

 periods of availability of marked shrimp from 

 various release sites. Caution in interpreting 

 these data is necessary since not all shrimp of a 

 marked group depart the release areas at the 

 the same time, are recovered immediately upon 

 reaching the offshore grounds, or are recovered 

 in proportion to their relative abundance. 



A few pink shrimp that were marked and re- 

 leased in Barnes Sound (5) remained in the 

 Sound for at least 174 days. Following the pink 

 shrimp age-size relation given by Kutkuhn, 4 

 we estimated the smallest shrimp released, 

 16.0 mm. carapace length (75.0 mm. total length), 

 to be about 60 days old. If 21-28 days are allowed 

 for larval and early postlarval development prior 

 to entrance into the nursery grounds, then it 

 appears that under certain conditions more 

 than 6 months of life may be spent in the estuaries. 

 Conversely, time spent in the estuaries may be 

 relatively brief. Only 35 days after the Shark 

 River release (6), one marked male, 20.2 mm. 

 carapace length (94.8 mm. total, length), was 

 recovered on the Tortugas grounds. Estimating 

 this shrimp's age as 79 days and subtracting 

 pre-estuarine entrance time, we found it ap- 

 parently spent less than 2 months in the estuarine 

 environment. The occurrence of pink shrimp 

 less than 20.0 mm. carapace length (92.5 mm. 

 total length) on the Tortugas grounds may indi- 

 cate that some individuals spent little or no time 

 on the more distant estuarine nursery grounds. 



' Kutkuhn. Joseph H„ Dynamics of a peimelil shrimp population and 

 management implications, p. 313, loc. dt. 



U.S. FISH AND WILDLIFE SERVICE 



