Table 1. — Tag releases and returns from east coast of U.S. bluefin tuna double tag study. 



were those described by the Food and Agricul- 

 ture Organization (1972). The 1971 releases 

 and returns in 1971 and 1972 are shown in 

 Table 1 by tagging agency and dart type. 



The notation and methodology in this study 

 follows Bayliff and Mobrand (1972): 



"ddk = Ft N^np^e "(^^ + ^ + 2L)<^ 



where: 



'ddk 



n 



dsk 



N, 



D 



IT 



time at the middle of the kth 

 period of length r (^ = 1, 2) , 



number of returns of double- 

 tagged fish retaining both tags 

 during the period centered at ^^ , 



number of returns of double- 

 tagged fish retaining only one tag 

 during the period entered at t^^, 



number of fish released with 

 double tags, 



portion of tagged fish which re- 

 main alive after the Type-I (im- 

 mediate) mortality has taken 

 place, 



portion of the tags which are 

 retained after Type-I (immediate) 

 shedding has taken place. 



= instantaneous 

 mortality. 



rate of fishing 



X — instantaneous rate of other mor- 

 tality (other includes natural 

 mortality, Type-I I (long-term) 

 tagging mortality and apparent 

 mortality caused by migration 

 from the fishery), and 



L = instantaneous rate of shedding 

 of tags. 



I 



Bayliff and Mobrand showed that 

 2n. 



In 



'ddk 



^dsk + 2/2ddfe 



-Lt, + Inp = Y, 



where Y,^ is an estimate of the log of the pro- 

 portion of tags retained up to time ^^. 



Estimates of Y^ are shown in Table 2. Esti- 

 mates of L and P are shown in Table 3. Although 

 some differences among categories are indicated, 

 a chi square test for differences in returns 

 among categories was not significant at the 90% 

 level of confidence. Thus the differences do not 

 appear to be large enough to rule out the use of 



Table 2. — Intermediate results in estimates of shedding 

 rates from 1971 U.S. east coast bluefin double tag study. 



1104 



