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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.

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.

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 (N2) solubility of 0.07 ml N2 ml−1 oil in odontocete fats, although solubility in blubber from many odontocetes exceeds this value. The present study examined N2 solubility in the blubber and mandibular fats of seven species across five families, relating it to lipid composition. Across all species, N2 solubility increased with wax ester content and was generally higher in mandibular fats (0.083±0.002 ml N2 ml−1 oil) than in blubber (0.069±0.007 ml N2 ml−1 oil). This effect was more pronounced in mandibular fats with higher concentrations of shorter, branched fatty acids/alcohols. Mandibular fats of short-finned pilot whales, Atlantic spotted dolphins and Mesoplodon beaked whales had the highest N2 solubility values (0.097±0.005, 0.081±0.007 and 0.080±0.003 ml N2 ml−1 oil, respectively). Pilot and beaked whales may experience high N2 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 N2 solubility of odontocete mandibular fats to better understand N2 dynamics and potential pathologies from gas/fat embolism.