Buckland et al : Estimating abundance of tuna-associated dolphin stocks in the eastern tropical Pacific 



The estimated trend from Figure 1 is downwards 

 until around 1983. Estimated abundance in 1976 and 

 1977 was significantly higher than in 1988 (P<0.05), 

 but there is some evidence of a recovery between 1983 

 and 1988 (P<0.05). Thus northern offshore spotted 

 dolphins appeared to decrease through the 1970s and 

 early 1980s, with numbers remaining stable or increas- 

 ing since. 



Figure 3 suggests there may have been a marked 

 decline in numbers of southern offshore spotted dol- 

 phins since the late 1970s. The smoothed 1988 estimate 

 is significantly lower than the smoothed estimates for 

 1977 and 1978, but there is evidence of an increase 

 since 1986 (P<0.05), after a relatively high unsmoothed 

 estimate for 1989. As shown by Anganuzzi et al. (1991), 

 southern offshore spotted dolphins appear to occupy 

 appreciably different regions from one year to another, 

 and the extent of mixing with northern offshore 

 spotted dolphins remains unclear. We therefore believe 

 that trend estimates for this stock are unreliable. The 

 estimated trends obtained by pooling data from the off- 

 shore stocks are shown in Figure 4. The estimates are 

 dominated by the data from the larger northern off- 

 shore stock, and the plot is similar to Figure 1. The 

 1988 smoothed relative-abundance estimate is signifi- 

 cantly higher than the 1983 and 1984 estimates, and 

 significantly lower than all estimates preceding 1979. 



1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 



Figure 2 



Smoothed abundance trends of northern offshore stock of 

 spotted dolphin Stenella attenuata in the eastern tropical 

 Pacific, excluding 1983 estimate. Broken lines indicate approx- 

 imate 85% confidence limits. See Figure 1 for more details. 



1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 



Figure 3 



Smoothed abundance trends of southern offshore stock of 

 spotted dolphin Stenella attenuata in the eastern tropical 

 Pacific. Broken lines indicate approximate 85% confidence 

 limits. See Figure 1 for more details. 



Figure 5 suggests that the eastern spinner dolphin 

 might have had a pattern of change similar to the 

 northern offshore spotted dolphin, although estimated 

 abundance in the late 1980s is roughly equal to that 

 in the mid-1970s, so depletion between 1975 and 1983 

 may have been less than for northern offshore spotted 

 dolphins. The 1988 smoothed estimate is just signifi- 

 cantly higher than the smoothed estimates for 1981 and 

 1982 (P<0.05). 



