FISHERY BULLETIN: VOL. 84, NO. 2 



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ESTIMATED AGE (years) 



Figure 4.— Fraction of sexually mature female spotted 

 dolphins versus age based on estimates of two readers. 

 Logistic curves are fitted to the data. Bars predict ages at 

 which 50% are sexually mature 



for the 1973-78 specimens (Reilley et al. 1983); the 

 mean ASM range for the 1981 sample was 11.6-11.7 



yr- 



Method Two 



The second method we used for estimating ASM 

 was to interpolate, from a maturation curve, the age 

 at which 50% of the specimens were mature Again, 

 sigmoid curve fits of the percent of mature speci- 

 mens as a function of age were used for the matura- 

 tion curves. For all aged samples combined, the 

 method predicts an ASM of 10.6-12.0 yr (for the two 

 readers), with an average of 11.3 yr. 



Our overall estimates of ASM (11.3 or 11.4 yr) dif- 

 fer markedly from the ASM estimated for ETP 

 spotted dolphins by Perrin et al. (1976) which was 

 9 tooth layers, "5.1 to 8.3 yr, depending on [which] 

 layering hypothesis is used" (p. 250). Our estimates 

 also differ from the ASM estimate for spotted 

 dolphins off the Japanese coast by Kasuya (1976) 

 which was 9 yr. 



Biases in ASM 



All of the above estimates of ASM are dependent 

 on two important assumptions. First, we assume that 

 counts of dentinal and cemental GLGs give precise 



and unbiased estimates of age Second, we assume 

 that our samples are unbiased with respect to the 

 maturity of the specimens collected. Potential biases 

 would result if the assumptions were invalid. Because 

 age estimates of the two readers differ significant- 

 ly (Reilly et al. 1983), the difference in ASM esti- 

 mates for the readers (1.5 yr) should be taken as a 

 minimum range in the ASM estimates. 



Color Pattern and Maturity 



Perrin (1969b) described the ontogenetic develop- 

 ment of color pattern in spotted dolphins in the ETP: 

 he divided the development into five sequential 

 phases (neonatal, two-tone, speckled, mottled, and 

 fused) based on patterns of ventral and dorsal spots. 

 Kasuya et al. (1974) described color-phase changes 

 in western Pacific spotted dolphins using somewhat 

 different definitions than those of Perrin (1969b), 

 although the description indicated that the onto- 

 genetic changes were similar to those observed by 

 Perrin. Perrin (1969b) found a close correlation be- 

 tween size and color pattern and (for a smaller sam- 

 ple) between sexual maturity and color pattern. 

 Kasuya et al. (1974) found that the development of 

 the adult color pattern in spotted dolphins from the 

 western Pacific coincides with the attainment of sex- 

 ual maturity. 



In our sample of spotted dolphins, there was con- 

 siderable overlap in age and length between animals 

 with different color patterns, but a correlation be- 

 tween color pattern and state of maturity was evi- 

 dent. In females from the aged sample, speckled 

 animals ranged from 3 to 18 yr, mottled from 6 to 

 32 yr, and fused from 10 to 38 yr. A similar overlap 

 occurred in body-length distribution from the overall 

 sample of females, 135-200 cm (n = 166), 140-210 

 cm (n = 179), and 155-220 cm (n = 188) for speckled, 

 mottled, and fused specimens, respectively. However, 

 96% of fused animals (n = 2,764), 50% of mottled 

 animals (n = 857), and only 4% of speckled animals 

 (n = 559) were sexually mature 



In addition, for a given length or age class, females 

 with a fused color pattern appeared to have been 

 mature for a longer time than animals with a mottled 

 pattern. For females of similar lengths, mature 

 specimens with a fused color pattern had more cor- 

 pora than those with a mottled color pattern (Fig. 

 5). Similarly for the aged sample, the fused speci- 

 mens within a given length group tended to have 

 more total corpora than mottled specimens, and 

 when specimens in the same body length categories 

 were of similar ages, fused animals had more total 

 corpora. 



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