Cockcroft and Ross Tursiops truncatus off southern Africa 



293 



Table 2 



Range in age (growth-layer-group) at which the vertebral 

 epiphyses of male and female bottlenose dolphins captured 

 off southern Africa were unfused, fusing, and fused. 



Unfused 



Fusing 



Fused 



Males 

 Females 



0-8 



(i-i; 



14 

 13 



>12 

 >12 



shows a clear discontinuity between 10 and 13 years 

 of age (Fig. 4), indicating that a two-stage growth curve 

 may better fit these data. 



The mean length and mass of the first five year- 

 classes (calculated from calves displaying whole, com- 

 pleted GLGs only) showed that growth rate during the 

 first year far exceeded that in any other. Mass in- 

 creases in the first year by some 255% of mean birth 

 mass, but increases over the subsequent 4 years slow 

 to 49%, 13.5%, 10.6% and 3.8%, respectively. In con- 

 trast, length increase is much less rapid over this same 

 period and is approximately 57%, 15.2%, 3.7%, 4%, 

 and 5.5%, respectively. In both males and females the 

 relationship between mass and length, up to asymptotic 

 values, is well defined by power ctirves (males, log mass 

 = -5.1 -f 3.06 X log length, r=0.97; females, log 

 mass = -4.7-1- 2.9 x log length, r=0.95). 



Both male and female bottlenose dolphins appear to 

 reach physical maturity between 12 and 15 years of age 

 (Table 2). The youngest physically mature animal was 

 12 years old while the oldest nonphysically mature 

 animal was 14 years old (Table 2). 



Female reproduction 



Only six (2.8% of the total catch and 12% of mature 

 females) of the captured females were pregnant, and 

 the growth of the six fetuses— length (cm) against mass 

 (kg)— was well defined by a linear regression (Fig. 5). 

 Although no estimate of gestation period was possible 



Figure 5 



Fetal growth in length and mass of bottlenose dolphins captured off 

 southern Africa, and a regression of the form (length = 23.914 -t- 

 0.006 X mass) drawn through these data. 



from these data, an estimate was obtained from the 

 relationship between neonatal and adult brain mass 

 (Sacher and Staffeldt 1974, in Perrin et al. 1977). A 

 neonatal brain mass of 639 g was estimated from the 

 mean brain mass of six stranded or captive-born 

 neonates in which the umbilicus was unhealed (Table 

 3). An asymptotic brain mass of 1460 g was calculated 

 from the mean brain volume of physically mature 

 females, although the variation in maximum size of 

 females would obviously affect this. Application of the 

 Sacher and Staffeldt equation gives a gestation period 

 of some 372 days. An alternative method of estimating 

 gestation period based on the relationship between 

 birth length and gestation period (Perrin et al. 1977) 

 yielded an estimate of 12.3 months or 374 days, assum- 

 ing a birth length of 103 cm. 



Birth date, to the nearest month, was back-calculated 

 for 25 captured calves less than 1-year-old by measur- 

 ing the width of deposited dentine as a proportion of 

 the mean width of the first GLG (Fig. 6). The mean 

 width of the first GLG layer was 279 ^m (A'^ = 29, range 

 229-331 \im) with a 95% CI of 10 \m\, indicating a max- 

 imum error of about 13 days. The subtraction of age 

 from date of capture (Fig. 6) suggests that most births 

 occurred in summer. 



In all females the majority of ovarian scars (80%) oc- 

 curred in the left ovary. The maximum number of scars 

 in any ovary was 1 1 , with no indication that ovary mass 

 decreased with the number of scars (Fig. 7). Age-, 

 mass-, and length-related ovulation rates appear ex- 

 tremely varied in bottlenose dolphins (Fig. 8). In only 

 one female was there one scar, so calculation of mean 

 age at first ovulation was impossible. This 13-year-old 



