considered in the subsequent analyses; (2) accurate 

 records are obtained of the numbers, dates, and 

 locations of recaptures; and (3) a comprehensive 

 tabulation is obtained of fishing effort in the area 

 where the experimental group is available. 



Experiments reported by Costello and Allen 

 (1962) and Zein-Eldin and Khma (1965) indicate 

 marking mth biological dyes has Uttle effect on 

 the individual shrimp. Experience gained during 

 earUer work (Costello and AUen, 1966) allowed 

 the capture-release phases to be carried out mth 

 negUgible injury to the Hv^e animals. 



Personnel stationed at principal landing ports 

 obtained recovery information on marked shrimp 

 from fishermen and packing plant workers. In 

 addition, they interviewed shrimp-boat captains 

 to determine the time, location, and extent of 

 fishing effort. We have a record of fishing effort 

 for all shrimp vessels trawling in the Sanibel 

 area. We have information on 77 percent of the 

 shrimp vessels fishing the Tortugas grounds; and 

 from these data we have estimated the effort 

 that applied to the area containing marked 

 shrimp. 



FIELD OPERATIONS 



To arouse their interest in the experiments, 

 shrimp fishermen were contacted individually 

 before the release of marked pink shrimp on the 

 Sanibel and Tortugas grounds. A reward of $2.00 

 was offered for retm-n of each marked shrimp. 



In both areas, the Biu-eau of Commercial 

 Fisheries chartered vessel Silver Bay cap- 

 tured shrimp and served as a platform for marking. 

 Shrimp captured on the Sanibel grounds March 19 

 to 22, 1962, were stain-marked by injection of 

 a 0.5 percent solution of fast green FCF, and 

 2,496 individuals were released at 26 randomly 

 selected sites in the trawling area (fig. 2). Shrimp 

 captured on the Tortugas grounds December 8 

 to 15, 1962, were stain-marked vnth a 0.25 per- 

 cent solution of Trypan blue, and 2,350 indi- 

 viduals were released at 16 randomly selected 

 sites in an area being fished by most of the fleet 

 at that time (fig. 2). 



Size compositions of marked shrimp released 

 in both experiments, as determined from samples 

 of marked shrimp ready for release, are shown in 

 figures 3 and 4. 



Adult pink shrimp, usually benthic, are par- 

 ticularly vulnerable to predation in the upper 



SMiBEL r 





r 



ei'W 



LEGEND 



I 1 AREA SHRIMP FOR MARKING ORIGINALLY 



I -I CAPTURED 



^B AREA MARKED SHRIMP RELEASED 



^.j-. EXTENT OF AREA OCCUPIED BY MARKED 

 / I SHRIMP 



POSITIONS AND NUMBERS OF RECAPTURES 

 OF MARKED SHRIMP 



•I • 2-9 © 10-20 © 21-50 © 60-90 

 Q 200-300 



GROUNDS ___ 



WROUESflS KEYS / KE'' *£ST 



Figure 2. — Capture, release, and recapture areas of 

 marked pink shrimp on the south Sanibel and the 

 Tortugas grounds. 



water layers, so an imderwater release device 

 described by Costello (1964) was used to lower 

 and release marked shrimp near the bottom. 



On the Sanibel groimds, 563 marked shrimp 

 or 22.5 percent of the experimental population 

 had been recovered by August 30, 1962. On the 

 Tortugas grounds, 784 marked shrimp or 33.3 

 percent of those released had been recovered by 

 March 29, 1963. 



TOTAL LENGTH (MM) 



:20- 







75 95 115 135 155 175 195 215 235 



_l I I I I L-J 1 I I I I I I I I I 



\u 



c 



SANIBEL GROUNDS 

 FLORIDA, MARCH 1962 



- r 29 2 mm CARAPACE 

 X LENGTH 



131 mm TOTAL LENGTH 



N= 205 (107 ff^ 98?) 



nin. i n , 



I I I T I I I I jl M I I M I I 1 I M I I I 



16 20 24 28 32 36 40 ,44 . 48 52 56 



CARAPACE LENGTH(MM.) 



Figure 3. — Size composition of a random sample from 

 the marked pink shrimp released on the south Sanibel 

 grounds. 



PINK SHRIMP MORTALITY ON SANIBEL AND TORTUGAS 



493 



