Table 1. — Fuhing effort and recoveries of stain-marked 

 shrimp, south Sanibel grounds, March 21 to May 29, 1962 



allowed measures of fishing effort to be converted 

 to fishing intensity, i.e., fishing effort per unit 

 area, the form required for subsequent analyses 

 (tables 1 and 2). 



ASSUMPTIONS AND JUSTIFICATIONS IN 

 THE ESTIMATION OF MORTALITY 



Any analytical approach to estimate mortahty 

 from mark-recapture data requires certain assump- 

 tions. Those we made are hsted below followed by 

 the evidence available to justify each. 

 Assumption 1 : 



Neghgible losses of marked shrimp due to 

 marking, handhng at release, or to loss of marks 

 after release. 



Justification : 



Experiments on survival of shrimp reported by 

 Costello and Allen (1962) indicate that stain- 

 marked shrimp have almost the same mortahty 

 as unmarked shrimp even in the presence of 

 predators. Evidence of the longevity of stain 

 marks (Dawson, 1957) excludes the hkehhood that 

 the marks fade or are lost over the period of the 

 present experiments. Shrimp were examined indi- 

 viduaUy before release to be certain that marks 

 were distinct. 



Table 2. — Fishing effort and recoveries of stain-marked 

 shrimp, Tortugas grounds, December 14, 1962 to February 

 7, 1963 



PINK SHRIIVIP MORTALITY ON SANIBEL AND TORTUGAS 



495 



