Common bottlenose dolphins (Tursiops truncatus) are apex predators and
indicators of localized ecosystem health. Accurate characterization of population
demography is crucial to parameter predictions. However, descriptions of age
growth investigations of odontocetes are limited to the postnatal life. In contrast,
the modeled scenario for terrestrial mammalian growth has been described along
a continuum of pre- and postnatal data. Few age distribution data exist for the
western Gulf of Mexico despite the fact that life tables enable demographic
comparisons among populations. The objective of this study was to characterize
age, growth, and population-level behavior of bottlenose dolphins along Texas.
This objective was accomplished by two discrete studies: age analysis, and
population-level behavior. Teeth from 290 stranded individuals were extracted for
the purposes of age determination. Curvilinear models (the Gompertz and the von
Bertalanffy) were fit to postnatal length-at-age data. Fetal age was determined for
408 suspected fetal length records using validated fetal growth trends and
empirical measurements from late-term fetuses. Growth analysis indicated that a
Gompertz model fit length-at-age data better than a von Bertalanffy model. A postnatal Gompertz model explained less variation than a combined pre- and
postnatal model (R2 = 0.9 and 0.94 respectively). The absolute growth rate and
rate of growth decay tripled with the inclusion of fetal length and age data. In the
second study, life tables were constructed for 280 individuals. Survivorship
curves, mortality rates, intrinsic capacity for increase, and the population growth
rate were calculated. Bottlenose dolphin mortality did not differ significantly by sex
or age class. Survivorship was best characterized by a type III curve. Analyses
indicated no substantial increase (r = -0.07), and that the population is not
replacing itself in the next time-step (y = 0.93). Bottlenose dolphins conform to a
number of eutherian mammalian trends: the production of precocial young, calving
seasonality, and rapid fetal growth rate. Population level behavior suggests a
population retraction possibly as a compensatory response to ecosystem
perturbation rather than a population decline. Reproductive information will
confirm population status and stability in the future. This study is the first to
demonstrate a significant impact of cetacean fetal growth parameters on postnatal
growth trajectory.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-08-3228 |
| Date | 2009 August 1900 |
| Creators | Neuenhoff, Rachel Dawn |
| Contributors | Marshall, Christopher D. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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