Understanding toothed whale (odontocete) diving gas dynamics is important given the recent atypical mass strandings of odontocetes ( particularly beaked whales) associated with mid-frequency naval sonar. Some stranded whales have exhibited gas emboli ( pathologies resembling decompression sickness) in their specialized intramandibular and extramandibular fat bodies used for echolocation and hearing. These tissues have phylogenetically unique, endogenous lipid profiles with poorly understood biochemical properties. Current diving gas dynamics models assume an Ostwald nitrogen (N 2 ) solubility of 0.07 ml N 2 ml −1 oil in odontocete fats, although solubility in blubber from many odontocetes exceeds this value. The present study examined N 2 solubility in the blubber and mandibular fats of seven species across five families, relating it to lipid composition. Across all species, N 2 solubility increased with wax ester content and was generally higher in mandibular fats (0.083±0.002 ml N 2 ml −1 oil) than in blubber (0.069±0.007 ml N 2 ml −1 oil). This effect was more pronounced in mandibular fats with higher concentrations of shorter, branched fatty acids/alcohols. Mandibular fats of shortfinned pilot whales, Atlantic spotted dolphins and Mesoplodon beaked whales had the highest N 2 solubility values (0.097±0.005, 0.081±0.007 and 0.080±0.003 ml N 2 ml −1 oil, respectively). Pilot and beaked whales may experience high N 2 loads during their relatively deeper dives, although more information is needed about in vivo blood circulation to mandibular fats. Future diving models should incorporate empirically measured N 2 solubility of odontocete mandibular fats to better understand N 2 dynamics and potential pathologies from gas/fat embolism.

Ages of Florida manatees (Trichechus manatus latirostris) can be estimated by counting annual growth layer groups (GLGs) in the periotic dome portion of the tympanoperiotic complex of their earbones. The Florida Fish and Wildlife Conservation Commission manages an archive of more than 8,700 Florida manatee earbones collected from salvaged carcasses from 1989 to 2017. Our goal was to comprehensively evaluate techniques used to estimate age, given this large sample size and changes to processing protocols and earbone readers over time. We developed new standards for estimating ages from earbones, involving two independent readers to obtain measurements of within- and between-reader precision. To quantify accuracy, precision, and error, 111 earbones from manatees with approximately known ages (first known as calves: “KAC”) and 69 earbones from manatees with minimum known ages (“MKA,” based on photo-identification sighting histories) were processed, and their ages were estimated. There was greater precision within readers (coefficient of variation, CV: 2.4–8.5%) than between readers (CV: 13.1–13.3%). The median of age estimates fell within the true age range for 63.1% of KAC cases and was at least the sighting duration for 75.0% of MKA cases. Age estimates were generally unbiased, as indicated by an average raw error ± SD of −0.05 ± 3.05 years for the KAC group. The absolute error (i.e., absolute value of raw error) of the KAC data set averaged 1.75 ± 2.50 years. Accuracy decreased and error increased with increasing known age, especially for animals over 15 years old, whose ages were mostly underestimated due to increasing levels of resorption (the process of bone turnover that obscures GLGs). Understanding the degree of uncertainty in age estimates will help us assess the utility of age data in manatee population models. We emphasize the importance of standardizing and routinely reviewing age estimation and processing protocols to ensure that age data remain consistent and reliable.

Cetacean integument serves many functional roles, including contribution to whole body buoyancy. The blubber of the integument of different cetacean species contains varying concentrations of triacylglycerols (TAG) and wax esters (WE); generally, these lipid classes have different densities. Integument can also experience a wide range of temperatures during a dive, so its density may change with depth. The goals of this study were to measure integument density and isolated blubber lipid density in three deep‐diving odontocete species (n = 3–4)—short‐finned pilot whales (Globicephala macrorhynchus), pygmy sperm whales (Kogia breviceps), and Gervais' beaked whales (Mesoplodon europeaus)—at different temperatures (6°C–35°C), and to relate these densities to lipid content and composition. Kogia and Mesoplodon integument and isolated lipids had high WE content (78.7–99.5 wt%) and were less dense (by 1.7%–9.3%) than those of Globicephala, which were composed predominately of TAG. Generally, densities increased as temperature decreased. Changes in integument densities mirrored those of isolated lipid densities, suggesting that blubber lipids are largely responsible for the buoyant properties of cetacean integument. These data demonstrate that the contribution of the integument to whole body density depends on lipid class and temperature, and therefore may provide useful, species‐specific correction factors for diving energetics models.

A leading human-related threat to the Florida manatee Trichechus manatus latirostris is collisions with watercraft, which account for 20-25% of reported mortalities. Quantitative threat assessments do not include information on all known manatee-watercraft interactions. These interactions often result in sublethal wounding, usually leaving multiple fresh external wounds in a variety of patterns. These wounds then resolve into well-healed scars. We characterized and quantified watercraft-related scar patterns (1 pattern = 1 strike event) on 2935 nonperinatal carcasses (>150 cm total length) that were recovered from 2007 through 2016 to compare the number of patterns by life stage, sex, and population region and across years. We used generalized linear mixed models to examine the effects of several factors on the probability carcasses having scars and on the number of scar patterns per carcass. The models indicated that approximately 96% of adults, approximately 70% of subadults, and approximately 34% of calves had watercraft-related scars. The raw data showed that 1 in 4 adults had been hit 10 or more times; 5 adult carcasses bore evidence of 40 or more strikes. On average, adult females had more scar patterns than did adult males. Manatees on Florida’s west coast had more scar patterns than did those on the east coast, while carcasses from the less populated Everglades had significantly fewer scar patterns than did those from the rest of the state. These results improve our understanding of the extent of sublethal injury of the Florida manatee caused by boat strikes.

The Critically Endangered status of North Atlantic right whales Eubalaena glacialis (NARWs) warrants the development of new, less invasive technology to monitor the health of individuals. Combined with advancements in remotely piloted aircraft systems (RPAS, commonly ‘drones’), infrared thermography (IRT) is being increasingly used to detect and count marine mammals and study their physiology. We conducted RPAS-based IRT over NARWs in Cape Cod Bay, MA, USA, in 2017 and 2018. Observations demonstrated 3 particularly useful applications of RPAS-based IRT to study large whales: (1) exploring patterns of cranial heat loss and providing insight into the physiological mechanisms that produce these patterns; (2) tracking subsurface individuals in real-time (depending on the thermal stratification of the water column) using cold surface water anomalies resulting from fluke upstrokes; and (3) detecting natural changes in superficial blood circulation or diagnosing pathology based on heat anomalies on post-cranial body surfaces. These qualitative applications present a new, important opportunity to study, monitor, and conserve large whales, particularly rare and at-risk species such as NARWs. Despite the challenges of using this technology in aquatic environments, the applications of RPAS-based IRT for monitoring the health and behavior of endangered marine mammals, including the collection of quantitative data on thermal physiology, will continue to diversify.

No abstract

Age estimation is useful for understanding population parameters and, in many vertebrates, relies on the principle that growth layer groups (GLGs) are deposited annually in specific tissues. In Florida manatees (Trichechus manatus latirostris), GLGs in earbones are used to estimate age at death. Opportunities to validate the rate of GLG deposition in earbones from manatees >15 years old are rare, yet important for ensuring accurate age estimation across the species’ lifespan. Tetracycline injection is a useful method for validating GLG interpretations, particularly when the exact age of an animal is unknown. Since 1997, we collected earbones from 10 manatees that were ≥13–69 years old at death and had been injected with tetracycline 9–37 years before death. The number of years since injection (YSI) was estimated by photographing earbone cross‐sections under ultraviolet light, measuring the distance between the fluorescent tetracycline mark and earbone edge, processing the earbones to visualize GLGs, superimposing the distance to evaluate the marks’ locations relative to GLGs, and counting the GLGs between the mark and earbone edge. Seven earbones had tetracycline marks, although 2 of the marks were dull or discontinuous. On average, estimated YSI was 5.6 (SD = 7.5) years less than the known YSI; however, the error was nearly always ≤2 years for manatees that had been injected <20 years before death, consistent with an annual rate of GLG deposition at younger ages. Resorption (i.e., bone turnover) that obliterated GLGs was likely why YSI was underestimated in old manatees with longer post‐injection intervals, although we cannot exclude the possibility that GLG deposition rate may slow in old age. We discuss how age, extrinsic stressors, life history events, and laboratory processing may affect tetracycline visibility, earbone growth, and GLG interpretation. Our study reinforces the challenges with accurately estimating the age of old individuals in long‐lived mammalian species. © 2021 The Wildlife Society.