350 



Fishery Bulletin 93(2), 1995 



Table 2 



Average numbers of dolphins killed in purse-seine sets in the eastern tropical Pacific by trip, for the 20 observed trips between 

 1964 and 1972. n equals the total number of observed dolphin sets during the trip. Also given are the six mean mortality per sets 

 (i?. iA ) used in Equation 4, where i equals 1 for large vessels (>600 tons carrying capacity) and 2 for small vessels (<600 tons 

 carrying capacity),,/ equals 1 for successful set (>l/4 ton yellowfin tuna) and 2 for unsuccessful set (<l/4 ton yellowfin tuna), k 

 equals 1 for when backdown was used and 2 for when backdown was not used, and where the subscript . indicates pooling across 

 that variable. Sample sizes of number of observed sets in each stratum are in parentheses. The data used are from 1) Smith and 

 Lo ( 1983) for the years 1964, 1965, and 1968, and 2) unpublished National Marine Fisheries Service tuna vessel observer data for 

 the years 1971 and 1972. 



(R. 



(R. 



(R. 



quantity of data, the CV's using just 17 trips were 

 somewhat higher. 



The 1973 observer data include 668 observed dol- 

 phin sets from 25 trips. My calculations of MPS from 

 those data resulted in values of 13.1, 7.9, 22.0, and 

 1.3 for the strata i?. 2 n» R.<>„., R. ■,,■,, and R. 

 respectively. 



•22- 



■ill' 



"•12" 



Discussion 



Nearly all the mortality of spotted dolphins was ob- 

 served in the northeastern stock (Table 4) because 

 very few dolphin sets were located outside the north- 

 eastern area prior to 1969 (Punsley, 1983). The few 

 sets that occurred outside this area prior to 1968 were 



sets that were not far offshore but were south of the 

 southern boundary of the stock area at 5°N (Punsley, 

 1983). Consequently, there were few observations of 

 MPS in western/southern area except in the area 

 south of 5°N and north of the Galapagos (Fig. 1). Al- 

 though this should have little effect on the estimates 

 for the northeastern stock, estimates of mortality for 

 the western/southern stock were not based on many 

 actual observations of MPS of spotted dolphins in 

 the western/southern area. There was complete 

 knowledge of the number of dolphin sets within the 

 western/southern area, but the estimates of mortal- 

 ity for that stock are based on the assumption that 

 MPS was the same in both stock areas. Annual mor- 

 tality estimates for the western/southern stock, 

 though relatively small, may therefore be biased. In 



