Results 



The estimated mortality based on the kill-per- 

 day method for each of the three periods was 

 24,000 animals (SE = 5,400) (1 January-26 

 March), 29,000 animals (SE = 5,300) (27 March- 

 4 July), and 53,000 animals (SE =21,000) (5 July- 

 end of fishing), to give a total kill of 105,000 ani- 

 mals (SE = 22,000) for 1976 (Table 3). 



Using the kill-per-set method, we computed 

 dolphin mortality estimates adjusted for non- 

 reporting of sets inside and outside the CYRA 

 (Table 4). The estimated total dolphin mortality 

 with this method was 104,000 animals (SE = 

 13,000). 



The closure dates for reaching the quota of 

 78,000 animals as projected at the end of June, 

 July, and September were in October. The fish- 

 ery itself, however, was not actually closed until 

 November, after a court hearing process. 



The annual quotas for 1977, 1978, and 1979 

 were 52,000, 42,000, and 31,000 animals, respec- 

 tively, and the mortality was monitored biweekly 

 by species/stock. Due to the improvement and 

 use of rescue techniques by the fishermen and 

 the motivation of tuna fishermen to reduce dol- 

 phin mortality, the kill-per-day estimates of 

 most of the species/stock have been below their 

 annual quotas. The kill-per-set estimate for an- 

 nual total dolphin mortality by U.S. seiners for 

 1977, 1978, and 1979 was 24,000 (SE = 3,500), 



19,000 (SE = 3,700) and 18,000 animals (SE = 

 2,200), respectively. 



Discussion 



Procedures for estimating dolphin mortality 

 have used the basic models tailored to suit the 

 existing conditions of the fishery and available 

 monitoring resources since 1976. The number of 

 strata for the kill-per-day method has been re- 

 duced because only vessel classes II and III are 

 fishing tuna with dolphin (the majority being 

 class III vessels), and all the vessels are required 

 to use a standard gear, i.e., super apron. More- 

 over, since 1979, there has been no quota on the 

 yellowfin tuna catch. Thus, the entire year is 

 "open" for fishing (Table 1). 



The kill-per-set method is more precise than 

 the kill-per-day method because the standard 

 error is smaller. However, in order to make 

 during-the-year estimates, procedures to collect 

 accurate information on the number of dolphin 

 sets for the whole fleet at regular intervals dur- 

 ing the year, yet need to be developed. Analysis of 

 use of the kill-per-set method indicated that the 

 number of vessel classes (eight) was unneces- 

 sarily large. A revision of the stratification 

 scheme for this method is currently in progress. 



The statistical techniques of monitoring and 

 estimating dolphin mortality can be applied to 

 other kinds of incidental catches. The 1976 dol- 

 phin mortality data, in particular, demonstrated 



Table 3.— Estimated kill by U.S. vessels in 1976 using kill-per-day method. 



Table 4.— Estimated kill by U.S. vessels in 1976 corrected for 

 nonreported sets (SE in parentheses) using kill-per-set method. 



'IATTC record 



the complexity of the situation where the selec- 

 tion of auxiliary variables for ratio estimator and 

 the stratification of data to reduce the variance 

 were not straight forward. These factors have to 

 be taken into account to ensure high precision of 

 the estimates. 



Literature Cited 



Allen, R. L., and M. D. Goldsmith. 



1981. Dolphin mortality in the eastern tropical Pacific 

 incidental to purse seining for yellowfin tuna, 1979. 

 Rep. Int. Whaling Comm. 31:539-540. 



400 



