TOTAL LENGTH (MM.) 



^25- 



§20- 



V) 



i^ 15-1 

 to 



m 



5- 



95 115 135 155 

 _l — 1 — l_,i I ] i__ 



TORTUGAS GROUNDS 

 FLORIDA, DECEMBER 1962 



27 5 mm CARAPACE 

 LENGTH 



124.0 mm TOTAL LENGTH 

 N = 62 (39 < 23?) 





ft. 



24 28 32 36 



CARAPACE LENGTH (mm) 



Figure 4. — Size composition of a random sample from 

 the marked pink shrimp released on the Tortiigas 

 grounds. 



DISPERSION OF THE MARKED SHRIMP 



On both fishing grounds, ])lots of the positions 

 of release and recapture of marked shrimp showed 

 that: (1) some marked shrimp dispersed following 

 release and (2) others remained within the im- 

 mediate area of release for at least 10 weeks. 



We used the release and recapture positions in 

 both experiments to define the areas containing the 

 marked shrimp. The outermost positions where 

 marked shrimp were released were plotted and 

 joined to enclose the original areas occupied; as 

 recoveries were received, the outermost recapture 

 positions were joined to delineate the expanding 

 areas occupied. Definitions of the successive areas 

 occupied were obtained \vith accumulation of sev- 

 eral days' recoveries. The location of fishing effort 

 was best established \vithin an area from infor- 

 mation compiled for 2-week intervals. For this 

 reason, we selected 2-week intervals as most 

 satisfactory. 



Dispersion of marked shrimp from the original 

 release areas proceeded at varying rates (figs. 5 

 and 6). Movements of the experimental group at 

 Sanibel were generally toward the west and south- 

 west. At Tortugas, dispersion was to the west and 

 northwest. The outUned areas achieved midway 

 between the first and last day of each succeeding 

 2-week period were selected as best descriptive of 

 the average situation in the i)eriods. At Tortugas, 

 for example, the area occupied by marked shrimj) 

 at the midpoint of the first 2-week period after re- 



494 



D 



PERIOD I 



Morcb 21 to April 3, 1962 



AREA CONTAINING EXPERIMENTAL 



POPULATION - 117 KM2 



(34 SQUARE NAUTICAL MILES) 



D 



PERIOO 3 

 April letollo) I, 1962 

 AREA CONTAINING EXPERIMENTAL 

 POPULATION- 212 KM^ 

 (62 SQUARE NAUTICAL MILES) 



D 



PERIOD 5 



My 16-29, 1962 

 AREA CONTAINING EXPERIMENTAL 

 POPULATION- 350 KM' 

 (102 SQUARE NAUTICAL MILES) 



D 



PERIOD 2 

 April 4 - 17.1962 

 AREA CONTAINING EXPERIMENTAL 

 POPULATION - 207 KM' 

 (60 SQUARE NAUTICAL MILES) 



■iANlHFl I \\''- 



D 



PERIOD 4 



M0( 2-15.1962 



AREA CONTAINING EXPERIMENTAL 



POPULATION - 347 KM' 



(lOI SQUARE NAUTICAL MILES) 



Figure 5. — South Sanibel grounds. Area occupied by the 

 population of marked pink shrimp in successive 2-week 

 periods, as determined from recapture locations. 



lease was 961 km.^ (280 square nautical miles). 

 The area occupied by marked shrimp any day of 

 that 2-week period was considered, therefore, to 

 be 961 km.2 (fig. 6). The outhnes shown (figs. 5 

 and 6) and information from interviews on the 

 location of fishing vessels enabled us to separate 

 fishing effort expended in the area containing the 

 experimental group of marked shrini]) from total 

 fishing effort on the grotmds. During Period 1, in 

 the Sanibel experiment, for example, the total 

 effort expended on the grounds on March 31, 1962, 

 was 16 boat-nights; the effort applicable to the 

 experimental ])opulation was 6 boat-nights (table 1). 

 Description of the expanding area occupied by 

 the marked shrimp permitted a refinement of the 

 original data. For each 2-week period, a factor 

 based on the relative size of the original area and 

 the expanded area was computed. This factor 



U.S. FISH AND WILDUFE SERVICE 



