238 



Fishery Bulletin 102(2) 



1970 



1980 



1990 



2000 



Year 



Figure 2 



Calf deficit per spotted dolphin (Stenella attenuata 

 attenuata) killed (D /; ) by year. Vertical lines indicate 

 95% confidence intervals. 



12000 



8000 -- 



4000 







= 12000  



8000 



4000 "- 



+■ 



Northeastern 



••At 



Western-southern 



»t Air * 



-+- 



-i- 



1970 



1980 1990 



Year 



2000 



Figure 3 



Total estimated calf deficit ^D lotal ) by year. Vertical 

 indicate 95% confidence intervals. 



by year indicated that the observed number of lactating 

 females in each set was significantly greater (P<0.05) 

 than the estimated number in 1977 for the northeastern 

 and the western-southern stocks and in 1979 for the west- 

 ern-southern stock. The difference was significantly less 

 in 1984 for the western-southern stock. Using 0.1 as our 

 type-2 error level, we determined through power analysis 

 that the minimum detectable difference («=0.05) between 

 the mean observed and estimated number of lactating 

 females per set across all years was approximately 0.08 

 and 0.09 in the northeastern and western-southern stocks 

 respectively. 



The observed number of calves per set, defined as the 

 number of dolphins less than 122 cm, was significantly 

 greater for both stocks, for all years combined, than the 

 values estimated in this paper ( Table 5 ). The overall mean 

 difference was 0.17 calves per set for the northeastern 

 stock and 0.12 for the western-southern stock. About 

 half of the years showed a significant difference for each 

 stock. In the comparison of the calf deficit by year, only a 

 few years showed significant differences in either stock 

 (Table 5). However, the estimated deficit tended to be 

 larger than the observed deficit. The paired t-test for all 



years combined was significant for the northeastern stock, 

 although the mean difference was only -0.06 missing 

 calves per set. The minimum detectable difference from 

 the power analysis for the mean number of calves per set 

 and mean calf deficit per set across all years was 0.06 and 

 0.08 respectively for both stocks. 



Discussion 



In the present study, we present an estimate of the number 

 of missing dependent northeastern and western-southern 

 offshore spotted dolphin calves in the tuna purse-seine 

 kill from 1973 to 1990 and from 1996 to 2000. The total 

 number of missing calves decreased through the time 

 series, which, because we estimated the calf deficit as a 

 function of the size of the kill, was a direct result of the 

 large reduction in the annual dolphin kill by the fishery. 

 Between 1973 and 2000, the shortage of calves in the 

 kill remained at a relatively constant fraction of the kill, 

 about 14 r i , for both stocks of pantropical spotted dolphins 

 (Fig. 2). On the assumption that suckling calves do not 

 survive separation from their mother ( Archer et al., 2001; 



