Cockcroft and Ross' Tursiops truncatus off southern Africa 



291 



Figure I 



A thin-etched section of a tooth from 

 "Dolfie", a captive-born bottlenose 

 dolphin captured off southern 

 Africa. The neonatal line (N) and the 

 end of each of six growth-layer 

 groups are marked. 



males and females, was best defined by derived von 

 Bertalanffy growth curves (Figs. 3,4) of the form: 



lit) = /,„,d - f-^c-'o))/' 



Asymptotic length and mass, calculated from the 

 mean length and mass of physically mature males (243 

 cm and 176 kg) and females (238 cm and 160 kg), were 

 slightly overestimated by the derived curve (Table 1), 

 but both show that the asymptotic length and mass of 

 males are greater than of females. There was no signifi- 

 cant difference between the mean mass of lactating and 

 nonlactating mature females (t = 0.236, P<0.01) which 

 may have contributed to this sexual dimorphism. 



Length and mass at birth L,,, predicted in Table 1 

 were almost identical to length and mass at birth (103 

 cm, range 86-115 cm, SD 7.6, Af = 26; 13.8 kg, range 

 9.1-21 kg, SD 2.9, A''= 15) calculated from the mean 

 length and mass of captive-born or stranded neonates 

 in which the umbilicus was unhealed. 



In both males and females, most growth occurred 

 during the first 10 to 12 years of life and thereafter 

 reached a plateau (Figs. 3,4). In females, both mass and 

 length increase in a smooth, continuous process with 

 no evidence of any discontinuity. In males, length in- 

 crease follows a similar pattern, whereas mass increase 



Figure 2 



Relationship between ^n-uwth layer-group counts in 

 the dentine and cement of male (■) and female (A) 

 bottlenose dolphins captured off southern Africa. 



