i Week in which experiment began. 



2 0.80 confidence intervals. 



• Thousands of pounds (whole shrimp). 



was represented in part by purposively selective 

 effort. It follows that the likelihood of recaptures 

 being subsequently recovered from commercial 

 landings had to be presumed essentially constant 

 throughout the experiment regardless of shrimp 

 size. 



RECOVERY PHASE 



Extensive publicity coverage preceded and con- 

 tinued during the experiment. With the as- 

 sistance of the Bureau's Branches of Fishery 

 Statistics and Market News, cooperation in the 

 retrieval of stained shrimp was solicited through 

 correspondence, market reports, and personal 

 interview from all industry segments as well as 

 from State conservation agencies and the Gulf 

 States Marine Fisheries Commission. The press, 

 radio, and television provided additional coverage. 

 A reward of $2 was offered for the return of any 

 marked shrimp when accompanied by information 

 regarding its place and date of capture. Posters 

 to this effect (fig. 4) were conspicuously placed in 

 all processing plants adjacent to the area in which 

 the experiment took place. Close contact with 

 fishermen and processors was maintained at all 

 times. 



Return of marked shrimp began immediately 



with 47 having been recovered before the end of 

 the experiment's first week, referred to herein as 

 the "period of release." Fortuitously, the State 

 management area in which the marked shrimp were 

 released (fig. 1) was opened to commercial fishing 

 2 days after the experiment got underway. In 

 all, 443 or 21 percent of the total number liberated 

 were eventually recaptured and returned for 

 verification. 4 Daily distribution of recaptures is 

 shown in figure 5. To facilitate subsequent- 

 analysis, they are grouped by calendar weeks 

 (top of fig. 5). 



Recovery continued strong for the first 8. weeks, 

 reaching a peak during the sixth week and then 

 dropping sharply (fig. 5) . No marked shrimp were 

 recovered after the 13th week. This abrupt at- 

 tenuation reflected a real decline in the experi- 

 mental population since associated recapture 

 (fishing) effort did not decrease but rose signifi- 

 cantly. Emigration of marked shrimp from the 

 range of effective fishing effort appeared negligible 

 (fig. 1), with no individuals being taken beyond 20 

 fathoms (only two outside 15 fathoms) or north of 

 the 25th parallel despite measurable expenditures 

 of effort at both locations (table 2). In general, 



' One marked shrimp returned 3 months after recapture was not included 

 in subsequent analyses. 



DYNAMICS OF A PENAEID SHRIMP POPULATION 



319 



