MYRICK ET AL.: REPRODUCTIVE BIOLOGY OF SPOTTED DOLPHINS 



12 



10 



< 

 a. 

 O 

 & 

 cc 

 o 

 o 



u. 



o 

 a. 



UJ 



ffi 



2 



8 



T 



M 



1 



F 



830 



IF 



256 



10 



M 



608 

 IF 



799 



IF 



T 



M 



1 

 76 



405 



T 



M 



20 



123 



T 

 F 

 1 



1 



F 



1 



3T 



8 



M 

 3 



F 



r 



I 



64 



T 



F 

 1 



T 



M 



1 



30 



T 

 M 



I 

 115 



T 



M 



J. 



90 



T 



M 

 724 



160 



170 



180 190 



LENGTH (cm) 



200 



210 



220 



Figure 5— Average number of corpora for mottled (M) and fused (F) color-phase specimens within each 5 

 cm length grouping for the overall sample of female spotted dolphins. Bars represent one standard error 

 from the mean. Sample sizes are shown. 



These results suggest that color phase may in- 

 dicate sexual maturity more accurately than either 

 age or length. Perrin (1969b) found 0% speckled (n 

 = 5), 60% mottled (n = 16), and 100% fused (n = 

 33) females to be sexually mature Using color phases 

 that roughly correspond to the late mottled and 

 fused stages of Perrin (1969b), Kasuya et al. (1974) 

 found that 93% (n = 30) of the spotted dolphins in 

 the third stage and 100% in the last (fourth) stage 

 of dorsal spotting were sexually mature A similar 

 relationship between maturity and color pattern 

 exists in male spotted dolphins in the ETP (Hohn 

 et al. 1985). Assuming that the proportion of mature 

 specimens in a given color phase does not change 

 within a population, it would be possible to estimate 

 the percentage of sexually mature specimens in a 

 sample without having to examine the ovaries for 

 corpora. 



Pregnancy Rate 



The annual pregnancy rate (APR) of a population 

 is the fraction of mature females that would be ex- 

 pected to give birth in any given year. APR can be 

 estimated as the average fraction of mature females 

 that are pregnant divided by the gestation time in 

 years. The variance of this estimate is approximated 



by 



var(APR) = (-P/7V) 2 var (T G ) 



+ (1/ZV) P(l - P)/n p 



where P is the proportion pregnant, T G is the 

 gestation time, and n p is the sample size used to 

 estimate P (Perrin and Reilly 1984). We use 0.958 

 yr (11.5 mo) as the gestation period for spotted 



253 



