Ontogenetic changes in the thermal and buoyant properties of Atlantic Bottlenose Dolphin (Tursiops truncatus) blubber

The thermal properties of cetacean blubber are influenced by its lipid content and thickness. In Atlantic bottlenose dolphins (Tursiops truncatus), both these features vary across ontogeny and with reproductive and nutritional status and, thus, may result in ontogenetic differences in blubber’s insulative quality. Lipid and water contents, and thermal conductivity and thermal insulation values of Atlantic bottlenose dolphin blubber were measured across fetal through adult life history categories (n = 36), and in pregnant females (n=4) and emaciated animals (n = 5). The thermal conductivities of deep and superficial blubber layers were also measured. Thermal conductivity varied significantly across ontogeny. Fetal through sub-adult life history categories had significantly lower mean thermal conductivity values (0.11 to 0.13 ± 0.01 W/m°C) than adults (0.18 ± 0.02 W/m°C). The conductivity of blubber from pregnant females was similar to non-adult categories, while that of emaciated animals was significantly higher than all other categories. The conductivity of superficial blubber was 37% higher than that of deep blubber. Across life history categories, the conductivity of superficial blubber was similar, while that of deep blubber was significantly greater in emaciated animals. Thermal insulation varied significantly across life history categories. Sub-adults and pregnant females had the highest insulation while fetuses and emaciated animals had the lowest insulation across life history categories. The insulation of neonates and juveniles was similar to that of adult dolphins. Heat flux measurements at the deep blubber surface were significantly higher than that at the superficial surface and this difference in heat flux was significantly correlated with blubber thickness. This pattern was not observed in control materials, polystyrene foam and white pine wood. In nutritionally dependant life history categories, changes in blubber’s thermal insulation resulted from changes in blubber thickness (i.e. quantity) and not thermal conductivity (i.e. quality). Conversely, in nutritionally independent animals, blubber quantity remained stable while blubber quality varied. Differences in conductivity through the blubber depth support the characterization of deep blubber as more insulative and metabolically active layer of lipid deposition and mobilization. Finally, blubber’s composition and its ability to absorb heat suggest that it likely is a phase change material. Blubber is the hypertrophied hypodermis of cetaceans composed primarily of adipocytes and structural fibers. Because the density of lipid is less than that of seawater, blubber has the potential to contribute to positive buoyancy. The blubber of Atlantic bottlenose dolphins (Tursiops truncatus) varies both in thickness and lipid content across ontogeny and with reproductive and nutritional status. This variation in blubber’s quantity and quality may significantly influence its contribution to buoyancy. To measure blubber’s buoyant force, its density was measured volumetrically and its volume was calculated at two body sites (trunk and tailstock), across an ontogenetic series of bottlenose dolphins and in pregnant females and emaciated animals. Lipid and water content were measured to correlate compositional changes with differences in blubber’s buoyant force. The density of blubber from the trunk region (mean ± standard error = 1043.1 ± 13.18 kg/m3) was similar to that of the tailstock (mean = 1077.1 ± 24.17 kg/m3) and these were not significantly different than the density of seawater (1026 kg/m3). Density in these regions was also similar between life history categories. Blubber volume in the trunk and tailstock regions increased over two orders of magnitude between fetuses and adults. The buoyant force of trunk blubber was similar across categories (mean = –0.91 ± 8.85N) and was not significantly different from neutral buoyancy (0N). Trunk blubber of emaciated animals was twelve times more negatively buoyant than that of adults. The buoyant force of tailstock blubber was similar between life history categories (mean = –0.30 ± 1.83 N). For groups with a sufficient sample size for statistical analyses (fetus, neonate, and juvenile), mean total buoyant force of blubber was 0.61 ± 7.45 N and was not significantly different between these groups. Despite significant differences in lipid content and volume across life history categories, blubber’s contribution to buoyancy remained neutral. Because this body compartment is nearly 25% of total body mass, it may be essential for this tissue to be neutrally buoyant. Pregnancy and emaciation can significantly influence blubber’s contribution to buoyancy and may impose additional locomotor costs associated with overcoming a positive or negative vertical force. vii

Comparative and Cumulative Energetic Costs of Odontocete Responses to Anthropogenic Disturbance

Odontocetes respond to vessels and anthropogenic noise by modifying vocal behavior, surface active behaviors, dive patterns, swim speed, direction of travel, and activity budgets. Exposure scenarios and behavioral responses vary across odontocetes. A literature review was conducted to determine relevant sources of disturbance and associated behavioral responses for several odontocete species (bottlenose dolphin, killer whale, harbor porpoise, and beaked whales). The energetic costs of species-specific responses to anthropogenic disturbance were then estimated. The energetic impact varies across species and scenarios as well as by behavioral responses. Overall, the cumulative energetic cost of ephemeral behavioral responses (e.g., performing surface active behaviors, modifying acoustic signals) and modifying swim speeds and activity budgets likely increases daily energy expenditure by ≤4%. In contrast, the reduction in foraging activity in the presence of vessels and/or exposure to sonar has the potential to significantly reduce individuals’ daily energy acquisition. Indeed, across all odontocete species, decreased energy acquisition as a result of reduced foraging undoubtedly has a larger impact on individuals than the increased energy expenditure associated with behavioral modification. This work provides a powerful tool to investigate the biological significance of multiple behavioral responses that are likely to occur in response to anthropogenic disturbance

Variability of Disk Emission in Pre-Main Sequence and Related Stars. II. Variability in the Gas and Dust Emission of the Herbig Fe Star SAO 206462

We present thirteen epochs of near-infrared (0.8-5 micron) spectroscopic observations of the pre-transitional, "gapped" disk system in SAO 206462 (=HD 135344B). In all, six gas emission lines (including Br gamma, Pa beta, and the 0.8446 micron line of O I) along with continuum measurements made near the standard J, H, K, and L photometric bands were measured. A mass accretion rate of approximately 2 x 10^-8 solar masses per year was derived from the Br gamma and Pa beta lines. However, the fluxes of these lines varied by a factor of over two during the course of a few months. The continuum also varied, but by only ~30%, and even decreased at a time when the gas emission was increasing. The H I line at 1.083 microns was also found to vary in a manner inconsistent with that of either the hydrogen lines or the dust. Both the gas and dust variabilities indicate significant changes in the region of the inner gas and the inner dust belt that may be common to many young disk systems. If planets are responsible for defining the inner edge of the gap, they could interact with the material on time scales commensurate with what is observed for the variations in the dust, while other disk instabilities (thermal, magnetorotational) would operate there on longer time scales than we observe for the inner dust belt. For SAO 206462, the orbital period would likely be 1-3 years. If the changes are being induced in the disk material closer to the star than the gap, a variety of mechanisms (disk instabilities, interactions via planets) might be responsible for the changes seen. The He I feature is most likely due to a wind whose orientation changes with respect to the observer on time scales of a day or less. To further constrain the origin of the gas and dust emission will require multiple spectroscopic and interferometric observations on both shorter and longer time scales that have been sampled so far.Comment: 42 pages, 10 figure

Recovery rates of bottlenose dolphin (\u3ci\u3eTursiops truncatus\u3c/i\u3e) carcasses estimated from stranding and survival rate data

Recovery of cetacean carcasses provides data on levels of human-caused mortality, but represents only a minimum count of impacts. Counts of stranded carcasses are negatively biased by factors that include at-sea scavenging, sinking, drift away from land, stranding in locations where detection is unlikely, and natural removal from beaches due to wave and tidal action prior to detection. We estimate the fraction of carcasses recovered for a population of coastal bottlenose dolphins (Tursiops truncatus), using abundance and survival rate data to estimate annual deaths in the population. Observed stranding numbers are compared to expected deaths to estimate the fraction of carcasses recovered. For the California coastal population of bottlenose dolphins, we estimate the fraction of carcasses recovered to be 0.25 (95% CI = 0.20– 0.33). During a 12 yr period, 327 animals (95% CI = 253–413) were expected to have died and been available for recovery, but only 83 carcasses attributed to this population were documented. Given the coastal habits of California coastal bottlenose dolphins, it is likely that carcass recovery rates of this population greatly exceed recovery rates of more pelagic dolphin species in the region