Neuenhoff, Rachel Dawn (2009-08). Age, Growth, and Population Dynamics of Common Bottlenose Dolphins (Tursiops truncatus) Along Coastal Texas. Master's Thesis. Thesis uri icon

abstract

  • 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.
  • 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.

publication date

  • August 2009