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Fishery Bulletin 88(2), 1990 



Testes were excised, weighed after removal of the 

 epididymis, and the dimensions (length x maximum 

 height X width) measured. The epididymis was visual- 

 ly checked for the presence of sperm and scored as 

 present or not; no microscopic evaluation was under- 

 taken. Testes from young animals (combined testis 

 mass ;$100 g) were preserved whole, while only a sec- 

 tion removed from the bigger testis of older males was 

 kept. Standard histological slides, approximately 5 jum 

 thick and stained with haemotoxylin and eosin, were 

 prepared from whole testes or from three locations 

 (outer, middle, and inner) of sections of large testes. 

 From each slide the diameter of a minimum of 10 cir- 

 cular seminiferous tubules was measured at a magni- 

 fication of 125 using an ocular reticule, to assess testis 

 development stage. 



Lactating females and calves caught together were 

 considered mother and calf pairs. Both left and right 

 ovaries were routinely collected and preserved from 

 all females. These were sectioned serially at about 

 1-mm intervals, and the number and dimensions of cor- 

 pora albicantia in each ovary and the presence and 

 dimensions of any corpus luteum were recorded. The 

 length and mass of any fetus present in the uterus was 

 recorded before preservation. Mammary glands were 

 assessed for the presence of milk and, for most lac- 

 tating females, the width, length, and depth measured. 



The state of physical maturity of animals was as- 

 sessed from the degree of fusion of the epiphyses to 

 the centra of midthoracic vertebrae (immature = un- 

 fused, maturing = fusing, and mature = fused). The 

 brain mass of neonates and calves was measured direct- 

 ly. That of adults was estimated by filling the skull with 

 coarse dry sand, after first sealing all apertures with 

 adhesive tape, measuring the volume of sand in a 

 measuring cylinder, and assuming this to represent the 

 brain mass. 



Age was determined from the number of growth- 

 layer groups (GLGs; sensu Perrin and Myrick 1980) 

 counted in the dentine and cement of longitudinal thin 

 sections of teeth. The largest mandibular or maxillary 

 teeth were used. Numerous methods of obtaining thin 

 sections were employed, including hand grinding on 

 1200-grade abrasive paper or between glass sheets 

 using jewelers rouge, or obtaining thin (~20 ^^m) 

 ground sections using a geological abrasive wheel. 

 However, the best results were achieved with a custom- 

 built, slow speed saw and diamond lapidary blade that 

 cut thin (120 ^m) sections. These were etched in 5% 

 formic acid for 5 minutes, washed in running water for 

 1 hour and dried and mounted on perspex slides using 

 cyanoacrylate glue. Sections were then viewed, at 8x 

 magnification, through a binocular microscope using 

 both transmitted polarized light and reflected light on 

 the pencil-rubbed etched surface of the tooth. 



Dentinal GLGs in all teeth were counted three times 

 by each of two independent observers. Additionally, 

 one observer (VGC) made a minimum of three cemen- 

 tal GLG counts in all teeth where the pulp was oc- 

 cluded, but only in a selection of teeth in which it was 

 not. Initially, dentinal and cemental GLG counts were 

 assessed separately, and the mean of any three counts 

 (dentinal or cemental) that were within 15% of one 

 another was accepted as the age of the animal. How- 

 ever, in teeth where counts varied by more than 15%, 

 further counts were done until any three were within 

 15% of one another. Finally, for teeth where the pulp 

 cavity was open, the mean of a combination of GLG 

 counts in both cement and dentine was accepted as an 

 estimate of age. Where occlusion of the pulp had oc- 

 curred, only mean cemental counts were used to 

 estimate age. 



The number of dentinal and cemental GLGs in the 

 teeth of one known-age animal ("Dolfie," PEM N6, 

 born 30 December 1972 and died 9 August 1979) were 

 also counted as above. In addition, because of the im- 

 portance of the age estimate of this animal, a third 

 observer (GJBR) counted GLGs in the dentine. 



Results 



Age and growth 



More than 6V2 but less than 7 dentinal GLGs were 

 counted in teeth of the known-age animal "Dolfie" (Fig. 

 1). This corresponded well with the actual age of 6 

 years and 8 months and indicated an annual deposition 

 of GLGs in the dentine. However, only six GLGs were 

 counted in the cement of this animal, indicating that 

 cemental GLGs probably reflect whole years only and 

 may underestimate age by 1 year. Despite this, cemen- 

 tal and dentinal GLG counts were taken to represent 

 age in years. 



Age estimates from dentinal and cemental GLG 

 counts of the teeth of 174 male and female Tursiops 

 were well correlated (/■ = 0.95 and /■ = 0.96, respective- 

 ly) up to approximately 12 GLGs; thereafter, counts 

 diverged with increasing age due to the closure of the 

 pulp (Fig. 2). The smallest individual from the nets was 

 29 kg and 125 cm, and had about 15% of the first GLG 

 formed (2 months old). The heaviest male was 204 kg, 

 the longest was 257 cm, and the oldest 42 years. The 

 corresponding parameters for females were 182 kg, 

 249 cm, and 43 years, respectively. 



The relationships of both body length and mass to 

 age, for captured Tursiops and stranded or captive 

 born neonates, were fitted to a number of growth 

 curves, including those of Gompertz, Richards, Putter, 

 and Schnute. However, growth with age, for both 



