NOTE Fernandez and Hohn: Age, growth, and calving season of Tursiops truncatus 
363 
coast of the United States, however, Mead and Pot- 
ter (1990) estimated length at birth (117 cm) as the 
mean length of 13 specimens classified as neonates 
on the basis of a folded or flaccid dorsal fin. Using 
the equivalent data set from the Texas sample (neo- 
nates), we found that the length at birth of mid- Atlan- 
tic coastal bottlenose dolphins was significantly differ- 
ent (7-test, P-0.02) from the estimate of 109.4 cm for 
Texas animals, but this result should be considered 
preliminary until larger sample sizes are available. 
Mean length at birth may best be estimated by 
using morphological characteristics. Tooth-layer 
deposition patterns proved to be accurate in compari- 
son to results from morphological data and can be 
valuable when morphological characteristics are not 
recorded. The method, however, is more time con- 
suming. In contrast, use of predicted lengths of 0-yr- 
old animals from a fitted growth curve may be inac- 
curate, as was the case with this sample. 
Strandings of neonates along the Texas coast are 
highly seasonal, with a mode in March. Using strand- 
ing data, Urian et al. (1996) found a significant dif- 
ference in calving season between bottlenose dolphins 
from the coast of Texas (citing this data set) and those 
from the central-west coast of Florida, including 
Sarasota Bay. Stranding patterns may not accurately 
reflect actual calving, however, because neonates that 
did not survive may be those that were born earlier 
or later than calves that did survive. In the Sarasota 
Bay area, Urian et al. (1996) found that the mean 
date of birth estimated from stranded neonates was 
16 days earlier than that estimated from sighting 
records of females with new calves, although this 
difference was not significant. They suggested that 
the photo-identification data may also be biased ow- 
ing to unequal and discontinuous distribution of sur- 
vey effort, a finding also made by Caughley and 
Caughley (1974). Further error may arise from lack 
of detection of neonates that stay very close to the 
female. Photo-identification studies of calving sea- 
son along the Texas coast identified a peak in num- 
ber of neonates in May (Shane, 1977). This later de- 
tection of neonates, in comparison with stranded 
animals, is consistent with the results from the cen- 
tral-west coast of Florida and limitations of the photo- 
identification method. 
The increase in proportion of females with age in 
the Texas sample is similar to a general pattern iden- 
tified in delphinids, with a slight bias towards young 
males and old females (Ralls et al., 1980; Perrin and 
Reilly, 1984; Wells and Scott, 1990). Some authors 
have attributed this shift to higher natural mortal- 
ity rates in males (Kasuya, 1976; Miyazaki, 1977; 
Wells and Scott, 1990). No direct or unbiased esti- 
mates of mortality are available for bottlenose dol- 
TabUe 4 
Sample sizes and descriptions of sexual and physical matu- 
rity in bottlenose dolphins, Tursiops truncatus, stranded along 
the coast of Texas. Reproductive data were not collected for 
males. 
Sex 
Sample 
Females 
Males 
unknown 
Total stranded with at 
least minimum data 
collected 
292 
373 
233 
With reproductive data 
57 
Number immature 
17 
Number mature 
40 
Largest immature (cm) 
235 
Shortest mature (cm) 
225 
With reproductive and 
age data 
25 
Number immature 
6 
Number mature 
19 
Oldest immature (yr) 
7.8 
Youngest mature (yr) 
9.8 
Youngest pregnant (yr) 
9.8 
With vertebrae examined 
for physical maturity 
25 
25 
12 
Number immature 
10 
16 
8 
Number maturing 
2 
2 
0 
Number mature 
13 
7 
4 
Largest immature (cm) 
253 
280 
253 
Shortest mature (cm) 
219 
237 
231 
With physical maturation 
and age data 
12 
11 
8 
Number immature 
2 
7 
4 
Number maturing 
1 
1 
0 
Number mature 
9 
4 
4 
Oldest immature (yr) 
15 
16 
9.9 
Youngest mature (yr) 
13 
18 
20 
phins from Texas, and patterns from stranded ani- 
mals may not accurately reflect the population. 
The proportion of specimens less than 1 year of 
age in the sample of stranded animals is higher than 
expected. In bottlenose dolphins from Sarasota Bay, 
Florida, Wells and Scott (1990) calculated that ani- 
mals in the same age class represented 3.4% of the 
population, and that the crude birth rate was 5.5% 
annually (range of 1.1-10.4% over eight years). The 
higher percentage ( 20%) of calves in the Texas sample 
most likely is due to the high rate of mortality in 
neonates and young calves. It is also interesting to 
speculate that cows with young calves may occupy 
more protected waters and, therefore, are more likely 
to wash ashore when they die, contributing to a strand- 
ing sample not representative of the population. 
Some of the specimens in the sample were notably 
large, e.g. a 300-cm male, a 335-cm female, a 280-cm 
