o. !Z 



>- 



CO 



Figure 7. — Mortality of marked pink shrimp, south 

 Sanibel grouni, March 21 to May 29, 1962. 



the theoretical numbers of recoveries of marked 

 shrimp that would have occurred in the first and 

 second 2-week periods following release of the 

 experimental population \vith fishing intensity 

 constant at 45.6 boat-nights per 2-week period. 

 For the Tortugas fishery, on the basis of 9,450 

 hours of fishing intensity per 2-week period, a 

 like procedure gave values of 269.3 and 188.5 for 

 ni and n2. With these numerical values for Ui and 

 Ui, and the No figures given in tables 4 and 5, we 

 may enter the following expressions from Beverton 

 and Holt (1957, p. 190). 



ni 



'»-© 



N, 



{'-?) 



X= 



:{•»-©}'- 



Til 



^"('-:t;)J 



60 T 



5 50" 



40-- 



30-- 



20-- 



I0-- 



Y= 5.953 -0.357X 

 N = 23I4 



e 



0-1 1 1 1 1 1 1- 



12345678 



WEEKS 



Figure 8. — Mortality of marked pink shrimp, Tortugas 

 grounds, December 14, 1962, to February 7, 1963. 



By applicatien of these expressions, we divide 

 the Z values given above into fishing mortality 

 (F) and "other losses" components (X). 



These calculations gave the following estimates: 



Sanibel— 

 Tortugas. 



Mortality 



I Fishing 

 (other.. 

 /Fishing 

 lOther.. 



Instantaneous 

 rates 



0.0689 

 .1644 

 .1385 

 .2185 



Rates (per- 

 cent) per 2- 

 week period 



6.8 

 14.8 

 13.1 

 19.7 



SUMMARY 



Mortality estimates for the Sanibel population 

 have not been previously reported. For the Tor- 

 tugas population, estimates derived here indicate 

 mortality higher than was reported by Iversen 

 (1962), but considerably lower than was calcu- 

 lated by Kutkuhn (1966). 



In either the Sanibel or Tortugas experiment 

 the values obtained for X (coefficient of other 

 loss) cannot be readily accepted as estimates of 



500 



U.S. FISH AND WILDLIFE SERVICE 



