% 



100 



Figure 3. — Weekly commercial catch and effort statistics 

 from the Tortugas pink shrimp fishery (statistical 

 Subareas 1-3), September-December 1961. 



what little movement was observed for the marked 

 shrimp during the course of the experiment seemed 

 to be in a west-northwesterly direction. As will be 

 shown later, the week in which most marked 

 shrimp were recaptured (sixth week, October 

 22-28) coincided with that during which the pre- 

 ponderance of the experimental population at- 

 tained the "minimum" commercial size designated 

 earlier. In other words, selective fishing by a 

 heretofore undetermined portion of the fishing 

 fleet ceased to be a factor at approximately this 

 point. 



Slightly less than three-fourths of the marked 

 returns were detected while handling catches at 

 sea. Because of the consistently small size of 

 shrimp taken during the experiment (fig. 3), the 

 great majority of catches had to undergo complete 

 processing ashore. Such treatment entailed re- 

 moving the head of each shrimp by hand, an 



Shrimp have been marked with blue and green biological stains to obtain infor- 

 mation on movements, growth, and rate of horvest. The color appears only on both 

 sides of the head (in the gills) as shown in the Illustration. 



LOOK FOR COLOR HERE 



A reword of $2.00 will be paid for stained shrimp when returned with the following 

 information: 



1. Exact place the shrimp was cawaht. 



2. Date the shrimp was cawaht. 



Notify by mail the U.S. Fish and Wildlife Service. No. I Rickenbacker Causeway, 

 Miami, Florida, or contact any Fish and Wildlife Service agent at port of landing. 

 Please include name of vessel with the information submitted. 



Figure 4. — Typical poster advertising reward for the 

 return of marked shrimp. Blue stain was employed in 

 both the Tortugas and Sanibel experiments. 



TOTAL I 



RECAPTURED > <- <D *t \n <T 

 WEEKLY J T <Q f - - 



O O ro O O 



Period ot reieose. 



2 4 6 9 10 12 14 

 WEEKS AFTER RELEASE 



SEP 



OCT NOV 



1961 



DEC 



A- Point ot which shrimp reached 

 minimum commercial size 



Figure 5. — Temporal distribution of fishing effort and of 

 marked shrimp recaptured during the Tortugas experi- * 

 ment. Vertical bars from the abscissa represent number 

 recaptured on indicated days. Vertical lines through 

 points on effort curve define 0.80 confidence intervals for 

 weekly effort estimates. 



320 



U.S. FISH AND WILDLIFE SERVICE 



