NOTE Fernandez and Hohn: Age, growth, and calving season of Tursiops truncatus 
361 
mated to be 9.8, 23, and 27 
years of age. A 4.8-year-old 
pregnant female, 245 cm 
long, was excluded from this 
sample owing to possible 
mislabeling of samples. No 
reproductive data were avail- 
able for males. 
Mean age and length at 
physical maturation could 
not be calculated owing to the 
small sample sizes (Table 4). 
Two specimens, a 280-cm 
male and a 253-cm female, 
were notable because they 
were relatively large yet phy- 
sically immature. 
Discussion 
Despite the widespread dis- 
tribution and high abun- 
dance of bottlenose dolphins 
along the Atlantic and Gulf 
of Mexico coasts of the United 
States, the majority of bio- 
logical information for this 
species has come from a few 
locations, a relatively small 
number of studies, and small 
sample sizes. Basic questions 
still remain throughout much 
of the range. The current 
data provided the opportu- 
nity to begin to evaluate simi- 
larities and differences in 
bottlenose dolphin life his- 
tory in relation to areas 
where previous studies had 
been conducted. 
Results from this study 
support the hypothesis that 
in bottlenose dolphins sexual 
dimorphism in body length is 
not exhibited at birth (Ser- 
geant et al., 1973; Hohn, 1980; Kasuya et al., 1986; 
Cockcroft and Ross, 1990) but does occur in adults 
(Read et al., 1993). Although a number of studies have 
concluded that sexual dimorphism in adult size does 
not exist in bottlenose dolphins from the Atlantic and 
Gulf of Mexico coasts of the United States (for ex- 
ample, Hohn, 1980; Hersh, 1987; Hersh et al., 1990; 
Mead and Potter, 1990), the contradictory results 
could be explained partly because sample sizes in 
□ 
m ■ 
□i 
D 1 □ 
D |s 
j—- — V u ‘ 
□ 
Females 
Mature ■ 
Immature ♦ 
Unknown □ 
j i i i i i_ 
_i I i i i i I i i i i I j 
20 
25 
30 
35 
40 
45 
£ 
a> 
c 
Age (yr) 
Figure 3 
Scatterplots of length at age for female and male bottlenose dolphins, Tursiops truncatus , 
stranded along the coast of Texas. The solid lines represent the predicted growth tra- 
jectory from the Gompertz model when specimens less than 1 yr old are excluded; growth 
between birth and age 1 was determined by using the independently estimated length 
at birth and the predicted length at age 1. The dashed lines represent the predicted 
growth trajectory from the Gompertz model with the entire data set. Although the 
asymptotic lengths are similar, the growth trajectories are different, particularly for 
females. 
earlier studies were small but also because these 
other studies did not fit a growth curve to obtain pre- 
dicted asymptotic lengths that could be directly com- 
pared (Read et al., 1993). The dimorphism at asymp- 
totic length may result from females diverting en- 
ergy to reproduction at the same ages that males are 
gaining girth and mass (Read et al., 1993) and thus 
would explain why sexual dimorphism occurs in 
adults, but not at birth. 
