setting for tuna on schools of porpoise. There are several 

 possible reasons why the quota was reached. One is that the 

 tuna fleet experienced an increased number of problem sets 

 which resulted in abnormally high levels of take. Another, 

 perhaps more important, reason is that tuna fishermen made 

 more sets on porpoise schools during 1986 than in 1985. This 

 was because tuna found with porpoise tend to be large and 

 large tuna brought a better price than smaller ones during 

 the generally depressed 1986 tuna market. Another possible 

 explanation for the high level of porpoise mortality in 1986 

 was the record high tuna catch rate of approximately 25 tons 

 of tuna per set. Large schools of tuna may be associated 

 with large schools of porpoise and, therefore, more porpoise 

 than usual may have been encircled per set. The large number 

 of tuna in the net may also have contributed to the high 

 mortality by making it more difficult to release porpoise 

 during the backdown procedure. 



The preliminary estimate of porpoise mortality in the 

 tuna fishery during 1987 was significantly less than the 1986 

 estimate with a total of 13,992 porpoise killed or seriously 

 injured. In 1987, the catch rate of tuna was somewhat below 

 20 tons of tuna per set, well below the record level of 1986, 

 suggesting that a lower incidental mortality of porpoise may 

 be correlated with a lower catch per unit effort of tuna. 



Despite the relatively low overall mortality observed in 

 1987, an unusually large number of eastern spinner dolphins 

 were taken. The 1984 amendments to the Marine Mammal Protection 

 Act established a quota of 2,750 for the eastern spinner 

 stock and, as this quota was approached, mortality was estimated 

 by the Service on a weekly basis rather than the customary 

 biweekly basis. At the close of the season, it was estimated 

 that 2,688 eastern spinner dolphins had been killed or seriously 

 injured. In comparison, during 1986, when the overall quota 

 of 20,500 porpoise was reached, the estimated mortality of 

 eastern spinners was only 1,608. One possible explanation 

 for the high eastern spinner mortality is that tuna, and, 

 hence, fishing effort, were concentrated in the area of the 

 eastern tropical Pacific Ocean where eastern spinner dolphins 

 are more abundant. 



Questions concerning the methodology that should be used 

 to estimate porpoise mortality were raised by the Commission 

 and others in 1986. As a result of deliberations among the 

 National Marine Fisheries Service, the Commission, and other 

 interested parties, it was determined that the same methodology 

 that had been used previously would be used in 1987, but that 

 further review of alternative approaches would take place. 

 In addition, the Service decided to provide 100 percent observer 

 coverage for the first trip of the U.S. tuna fleet in 1987. 

 In response to comments from the tuna industry that the metho- 



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