Manatee Research Articles

Habitat selection and abundance of West Indian manatees Trichechus manatus at the margins of their expanding range

Habitat selection and abundances at range margins during geographic expansion may influence movement into new areas, shaping the trajectory of climate-driven changes in species distribution. The West Indian manatee is an ideal species to study how habitat selection influences range expansion because its presence has rapidly increased during the past 2 decades in the northern Gulf of Mexico (nGoM), a region outside its historical range. We estimated the habitat selection and abundances of manatees in coastal Alabama waters along the nGoM coast using resource selection functions and N-mixture models, respectively. Warm season (May-Nov) manatee abundances were estimated at 25 and 34 manatees at any given time in coastal Alabama waters in 2010 and 2019, respectively. Manatees primarily used the Mobile-Tensaw River Delta and Dog River areas, selecting nearshore shallow water habitats proximate to submerged aquatic vegetation. Distance to boat ramps and human population density had stronger effects on opportunistic sighting data but remained important for tagged data, indicating that manatee habitat selection overlapped with humans. Temperature strongly predicted manatee sightings; most sightings occurred when temperatures were >20°C. Our data indicate that the key interacting factors likely to moderate manatee range expansion, and therefore be important to management and conservation of this species, include increased sea temperature, availability of nearshore habitat with submerged aquatic vegetation, and regional manatee population dynamics. As environmental conditions at the range margins continue to become more favorable to manatees and areas within the range core decline in quality, areas at the range margins may become increasingly important.

Characterization of novel papillomavirus from free-ranging Antillean manatee Trichechus manatus manatus with genital papillomatosis.

The Antillean manatee Trichechus manatus manatus is an Endangered species living along the Atlantic coasts of the Americas from Florida (USA), throughout the Caribbean, to Brazil. In July 2020, a manatee with multiple wounds due to boat-inflicted trauma was rescued from the coast east of Cayo Mata, Salinas, Puerto Rico. This manatee had neutropenia, leukopenia, and monocytosis associated with immunosuppression and nutritional deficiency anemia, as well as bacteria and fungi within the lesions. The manatee had genital lesions which included papules and linear plaques, microscopically characterized by mucosal hyperplasia with cytopathic changes typical of papillomavirus infection. Superficial epithelial cells had strong nuclear immunolabeling when examined using a monoclonal antibody specific to papillomavirus. The sequencing data of PCR products with papillomavirus-specific degenerative primers indicated that these lesions contained a novel manatee papillomavirus (Trichechus manatus papillomavirus, TmPV). The genomic DNA was amplified using a rolling circle amplification, and fully sequenced to be 7586 bp (GenBank accession no. OK073977). Other TmPVs were previously isolated from Florida manatees T. manatus latirostris. This novel virus was designated TmPV type 5 (TmPV5) based on its genomic characterization and sequence comparison. The TmPV5 genome shared 50.7, 48.9, 69.4, and 62.1% similarities with TmPV1, TmPV2, TmPV3, and TmPV4, respectively. TmPV5 is classified in the genus Rhopapillomavirus together with other manatee papillomaviruses. After 2.5 mo of veterinary treatment and rehabilitation, the manatee recovered and was released. This is the first report of papillomatosis in a free-ranging Antillean manatee.

Behavior related vocalizations of the Florida manatee (Trichechus manatus latirostris)

AbstractFlorida manatees (Trichechus manatus) produce five broadly defined call types (squeaks, squeals, high squeaks, chirps, squeak‐squeals) but their use in social and nonsocial settings is unclear. The goal of this study was to investigate whether call categories and structure of manatee vocalizations varied with behavior. Multiple hydrophones were used to record vocalizations in four different environments and broad behavioral states. Vocalizations recorded from resting, cavorting, stressed, or feeding wild animals were subjected to mixed linear effects models to test whether vocalizations produced varied with behavior and calf presence. Measures of duration, entropy, and frequency modulation were extracted from vocalizations to investigate if structural parameters differ among behaviors. Although all five call categories were recorded, results suggest manatees vocalize using primarily three call types and vary the structure of the call based on behavior. High squeaks were correlated with calf presence. High entropy squeals were proportionally higher during cavorting suggesting they may be related to a heightened state of arousal. Squeaks were the dominant call type produced and were longer in duration and higher in frequency modulation when animals were stressed. This research provides a foundation for comparative studies on vocal behavior for the Florida manatee as well as studies on related species.

Mitochondrial Genetic Diversity, Population Structure and Detection of Antillean and Amazonian Manatees in Colombia: New Areas and New Techniques.

The Antillean manatee (Trichechus manatus) and the Amazonian manatee (Trichechus inunguis) are distributed in rivers in the Caribbean and Amazonian region of Colombia respectively. For 30 years, genetic information has been obtained from these populations in order to inform conservation programs for these endangered species and decide on the location to release them back to the wild. However, in previous studies, samples from rivers in some areas of the country were not included, given the difficulties to access these regions due to either logistic or safety issues. In this study, we analyzed mitochondrial DNA (mtDNA) control region (CR) sequences of from samples of T. manatus (n = 37) and T. inunguis (n = 4) (410 and 361 bp, respectively), obtained in new and previously unexplored rivers and bays in the country, including Santa Marta, Urabá Gulf, Ayapel Marsh (San Jorge River Basin), Meta River and Magdalena Medio and the low Magdalena River (Cesar Province and Canal del Dique) as well as additional samples from Puerto Nariño in the Colombian Amazon. Our results included the discovery of two newly described mtDNA CR haplotypes for T. manatus. In addition, we confirmed significant population differentiation at the mitochondrial level between the Magdalena and Sinú rivers and differentiation among areas of the same river, including the middle and low Magdalena River. This differentiation may be related to anthropic changes in the river since construction of the Canal del Dique in the XVI century. We also tested environmental DNA sampling and analyses techniques to evaluate its potential use for manatee detection and monitoring in bodies of water in Colombia, in order to evaluate new areas for future manatee conservation initiatives. We emphasize the need to continue using genetic information to provide evidence on the potential best locations to undertake animal release to prevent outbreeding depression.

Studying Antillean manatees’ (Trichechus manatus manatus) temperament in zoological parks: exploration of boldness, sociality and reactivity to humans

Temperament, i.e. consistent inter-individual differences in behavior, has been documented in many species. Especially, boldness-shyness continuum is the ecologically relevant trait most frequently used to describe temperament among species. Reactions along the bold-shy axis demonstrate an organism’s ability to cope with environmental conditions and reflect its response to environmental stress. Our study investigated the existence of boldness-shyness continuum in 16 captive Antillean manatees (Trichechus manatus manatus) housed in 2 zoological parks. We first aimed to establish a valid methodology to measure boldness and shyness using behavioral tests. Additionally, our study explored 2 other potential temperament dimensions: sociality and reactivity to humans, and their association with boldness. Finally, since animals were kept under human care, we investigated human perception on manatees’ temperament. We conducted behavioral tests i.e. novelty tests involving novel objects, a novel sound, and an unfamiliar human. We recorded behaviors related to exploration as well as social interactions (i.e. physical proximity, social contacts) and we assessed manatees’ reactivity to humans through a participation score during hand-feeding sessions. Finally, we collected keepers’ subjective impression about individuals’ temperament through traits rating method. To our knowledge, this is the first paper that tested manatees’ reactions to different novel stimuli in order to determine their temperament. Our results first allowed us to identify the most relevant stimuli and variables to measure boldness and to classify individuals as bolder or shier. Individuals characterized as bolder displayed significantly more approach, longer approach and more contact toward stimuli than shier individuals. Moreover, boldness score was significantly associated with physical proximity with conspecifics, as well as with the participation score to hand-feeding sessions in one zoo. Finally, surveys completed by keepers were reliable and positive associations were found between rated items and behavioral observations. These findings support that as many species, manatees demonstrate boldness-shyness traits. More investigations on a larger sample size are needed to explore manatees’ temperament dimensions, and how these traits could modulate their interactions with their conspecifics and their environment. Studying manatees’ temperament could help improving the management and welfare of the species under human care. It could also facilitate their management in wildlife reserves by understanding manatees’ movements and evaluate the anthropogenic impact on wild populations.

Serum Reference Intervals of Fat-Soluble Vitamins D and E in Wild Florida Manatees (Trichechus manatus latirostris) and Possible Implications for the Health of Manatees in Managed Care.

Serum levels of alpha-tocopherol (vitamin E) and 25-hydroxyvitamin D (vitamin D) were measured in 25 wild Florida manatees (Trichechus manatus latirostris) from Crystal River National Wildlife Refuge, Citrus County, Florida, US. The samples were collected during the 2017 and 2018 winter health assessments. Reference intervals for alpha-tocopherol were 0.15-3.2 µg/L with mean value of 0.76 µg/mL and for 25-hydroxyvitamin D were 4.3-23 nmol/L with a mean of 13.88 nmol/L. Four, long-term captive manatees and nine manatees in rehabilitation were available for comparisons. Alpha-tocopherol levels were within the established range for free-ranging manatees. Mean 25-hydroxyvitamin D levels in long-term captive and manatees in rehabilitation fell well outside the reference interval for free-ranging manatees, being six- to sevenfold higher. The absence of significant differences in alpha-tocopherol between wild and captive manatees may not have any significant direct clinical implications but may warrant an investigation into other antioxidant mechanisms in manatees. The elevated 25-hydroxyvitamin D levels seen in captivity were unexpected and, in a few individuals, may pose a health challenge. Calcium is known to be elevated in captive manatees as well; a close examination of a potential hypervitaminosis D and hypercalcemia may be warranted.

Analysis of body condition indices reveals different ecotypes of the Antillean manatee

Assessing the body condition of wild animals is necessary to monitor the health of the population and is critical to defining a framework for conservation actions. Body condition indices (BCIs) are a non-invasive and relatively simple means to assess the health of individual animals, useful for addressing a wide variety of ecological, behavioral, and management questions. The Antillean manatee (Trichechus manatus manatus) is an endangered subspecies of the West Indian manatee, facing a wide variety of threats from mostly human-related origins. Our objective was to define specific BCIs for the subspecies that, coupled with additional health, genetic and demographic information, can be valuable to guide management decisions. Biometric measurements of 380 wild Antillean manatees captured in seven different locations within their range of distribution were obtained. From this information, we developed three BCIs (BCI1 = UG/SL, BCI2 = W/SL3, BCI3 = W/(SL*UG2)). Linear models and two-way ANCOVA tests showed significant differences of the BCIs among sexes and locations. Although our three BCIs are suitable for Antillean manatees, BCI1 is more practical as it does not require information about weight, which can be a metric logistically difficult to collect under particular circumstances. BCI1 was significantly different among environments, revealing that the phenotypic plasticity of the subspecies have originated at least two ecotypes—coastal marine and riverine—of Antillean manatees.

EVALUATION OF THE PHARMACOKINETIC BEHAVIOR OF TULATHROMYCIN (DRAXXIN) IN FLORIDA MANATEES (TRICHECHUS MANATUS LATIROSTRIS) UNDERGOING MEDICAL REHABILITATION.

Florida manatees (Trichechus manatus latirostris) frequently present to rehabilitation care facilities for various conditions, including boat strike trauma, cold stress syndrome, and brevetoxicosis. Throughout the course of treatment, antimicrobial use to treat respiratory disease is frequently warranted. To date, clinicians have extrapolated dosages based on established information available in bovine and equine medicine. The routes of administration, efficacy, and treatment intervals are considerations in dealing with critical wild animals. The use of tulathromycin, a triamilide antibiotic, has been studied in multiple domestic species of economic importance, including cattle, small ruminants, and swine, and has revealed efficacy against respiratory diseases. Given this information, this antibiotic has also been used in manatees with positive clinical outcomes. This study employed sparse sampling and evaluated banked plasma samples at various time intervals post-tulathromycin administration obtained during the clinical treatment course of nine animals during their rehabilitation. Preliminary pharmacokinetic analysis following administration of a single dose estimated a half-life of 33.75 h and volume of distribution per fraction absorbed (Vz/F = 4.29 L/kg). The pharmacokinetic behavior of tulathromycin in Florida manatees can be used to optimize dosage regimens in this species.

PRESENTATION AND MANAGEMENT OF DENTAL PAD FRACTURES IN TWO FLORIDA MANATEES (TRICHECHUS MANATUS LATIROSTRIS).

The Florida manatee (Trichechus manatus latirostris) has well-developed keratinized dental pads at the most rostral aspect of their mouth to assist with mastication. This unique development is thought to be an adaptive response to their highly abrasive diets that contain phytoliths and sediments that may accelerate dental wear. In May 2013, two Florida manatees presented with multiple fractures in their inferior dental pads. The fractures were successfully managed with nutritional modifications, dental pad trimming, and vigilant monitoring through behavioral husbandry training. Signs of spontaneous healing were observed as early as 60 days after initial presentation with subsequent full resolution. Although surgical intervention was planned, the spontaneous healing mitigated significant health risks associated with the procedure. To the authors' knowledge, these are the first reported cases of dental pad fractures and their spontaneous healing and resolution in manatees.

West Indian Manatees Use Partial Migration to Expand Their Geographic Range Into the Northern Gulf of Mexico

Partial migration provides a mechanism for species to shift their geographic ranges into new, environmentally favorable regions but has been poorly studied as a means to alleviate effects of climate change. Populations at the edge of their geographic range are ideal to investigate how migratory behaviors may enable range expansion as adjacent areas become more climatically favorable. We determined the contribution of partial migration to the range expansion of West Indian manatees (Trichechus manatus) using GPS data from tagged individuals that migrated between the northern Gulf of Mexico (nGoM) and primary habitat in peninsular Florida. Most of these manatees migrated to the nGoM annually and exhibited high site fidelity among years. Many individuals spent cumulatively more time in the nGoM than in peninsular Florida, indicating the nGoM is a regular part of their geographic range, and they returned to peninsular Florida to meet temperature-related physiological needs for survival. Autumn migrations most frequently terminated at Crystal River, Florida, and manatees that commenced migration late in the season stopped less frequently and had more directed movements. Spring migrations most frequently terminated at Mobile Bay, Alabama, and several manatees quickly and directly migrated from Florida to nGoM stopover sites. Migrations ranged from 10 to 133 days in length, and variation in duration was primarily driven by use of stopover sites and directedness of travel. These data confirm partial migration as an important component of manatee migratory behavior that has already enabled range shifts for manatees on the U.S.A. Gulf of Mexico coast and has potential to facilitate future responses to climate change. As the most common type of migration across the animal kingdom, partial migration may provide a global mechanism for a diverse variety of species to resist the range limiting effects of climate change.

Superluminal Communication in the Bible and God’s design of marriage

Sex, Orgasms, Love and Marriage all in God's pleasurable purpose, by God's grace and for God's glory. Genesis 3.6-7 suggests sin came from the man thus they knew they were naked ONLY AFTER the man ate, and quantum mechanics provides a first generation scientific understanding to support the biblical claim that sin came from the man. Please read my only other paper for now - Genesis 3 quantum events

Evaluation of Different Extraction Methods for the Analysis of Per- and Polyfluoroalkyl Substances in Dried Blood Spots from the Florida Manatee (Trichechus manatus).

Per- and polyfluoroalkyl substances (PFAS) are environmental contaminants linked to adverse health effects in humans and wildlife. Marine mammals, particularly manatees, have shown potential as sentinels for evaluating the presence and effects of anthropogenic chemicals. However, traditional blood collection techniques with marine mammals can be challenging, highlighting the need for improved strategies. In the present study, four different methods for the extraction of PFAS from dried blood spots were evaluated. Environ Toxicol Chem 2021;40:2726-2732. © 2021 SETAC.

Metabolic trade-offs in tropical and subtropical marine mammals: unique maintenance and locomotion costs in West Indian manatees and Hawaiian monk seals.

ABSTRACTUnlike the majority of marine mammal species, Hawaiian monk seals (Neomonachus schauinslandi) and West Indian manatees (Trichechus manatus latirostris) reside exclusively in tropical or subtropical waters. Although potentially providing an energetic benefit through reduced maintenance and thermal costs, little is known about the cascading effects that may alter energy expenditure during activity, dive responses and overall energy budgets for these warm-water species. To examine this, we used open-flow respirometry to measure the energy expended during resting and swimming in both species. We found that the average resting metabolic rates (RMRs) for both the adult monk seal (753.8±26.1 kJ h−1, mean±s.e.m.) and manatees (887.7±19.5 kJ h−1) were lower than predicted for cold-water marine mammal species of similar body mass. Despite these relatively low RMRs, both total cost per stroke and total cost of transport (COTTOT) during submerged swimming were similar to predictions for comparably sized marine mammals (adult monk seal: cost per stroke=5.0±0.2 J kg−1 stroke−1, COTTOT=1.7±0.1 J kg−1 m−1; manatees: cost per stroke=2.0±0.4 J kg−1 stroke−1, COTTOT=0.87±0.17 J kg−1 m−1). These lower maintenance costs result in less variability in adjustable metabolic costs that occur during submergence for warm-water species. However, these reduced maintenance costs do not appear to confer an advantage in overall energetic costs during activity, potentially limiting the capacity of warm-water species to respond to anthropogenic or environmental threats that require increased energy expenditure.

A hidden Markov model for estimating age-specific survival when age and size are uncertain.

Estimates of age‐specific survival probabilities are needed for age‐structured population models and to inform conservation decisions. However, determining the age of individuals in wildlife populations is often problematic. We present a hidden Markov model for estimating age‐specific survival from capture–recapture or capture–recapture–recovery data when age is unknown and indicators of age, such as size and growth layer counts, are imprecise. The model is evaluated through simulations, and its implementation is illustrated with maximum likelihood and Bayesian approaches in commonly used software. The model is then applied to genetic capture–recapture data of Florida manatees to estimate age‐ and time‐variant survival probabilities. The approach is broadly applicable to studies aiming to quantify age‐specific effects of environmental change and management actions on population dynamics, including studies that rely on minimally invasive methods such as genetic and photo identification.

Monitoring abundance of aggregated animals (Florida manatees) using an unmanned aerial system (UAS)

Imperfect detection is an important problem when counting wildlife, but new technologies such as unmanned aerial systems (UAS) can help overcome this obstacle. We used data collected by a UAS and a Bayesian closed capture-mark-recapture model to estimate abundance and distribution while accounting for imperfect detection of aggregated Florida manatees (Trichechus manatus latirostris) at thermal refuges to assess use of current and new warmwater sources in winter. Our UAS hovered for 10 min and recorded 4 K video over sites in Collier County, FL. Open-source software was used to create recapture histories for 10- and 6-min time periods. Mean estimates of probability of detection for 1-min intervals at each canal varied by survey and ranged between 0.05 and 0.92. Overall, detection probability for sites varied between 0.62 and 1.00 across surveys and length of video (6 and 10 min). Abundance varied by survey and location, and estimates indicated that distribution changed over time, with use of the novel source of warmwater increasing over time. The highest cumulative estimate occurred in the coldest winter, 2018 (N = 158, CI 141–190). Methods here reduced survey costs, increased safety and obtained rigorous abundance estimates at aggregation sites previously too difficult to monitor.

Brucella Infection Investigation in Cetaceans and Manatees in Northeast Brazil.

Among the bacterial infections that impair the health status of marine mammals, those caused by Brucella spp. are the most reported worldwide. Brucella infections in marine mammals can result in acute or chronic disease and are associated with variable clinical outcomes, depending on the organ involved during the infectious process, infection route, host immunity, and strain pathogenicity. Asymptomatic infections may also occur. The current study expands the investigation of Brucella infection in northeast Brazil by analyzing 19 dead, stranded cetaceans and 52 Antillean manatees Trichechus manatus manatus. The manatees included 8 dead, captive manatees and 44 live specimens, of which 10 were analyzed only after reintroduction into the wild as part of a rehabilitation program, 9 were analyzed both while in captivity or semi-captivity and after reintroduction, 20 were sampled only in captivity or semi-captivity, and 5 were free-living manatees. Serological tests were used to screen for antibodies against smooth Brucella spp. Whole blood, swabs, and tissue samples were screened for Brucella spp. DNA by PCR. Samples with positive PCR results were cultured for Brucella spp. isolation. All manatees yielded negative results in serological and molecular tests. Brucella spp. DNA was detected in the kidney of one adult Guiana dolphin Sotalia guianensis exhibiting necrosis in the liver. No growth of Brucella spp. was observed via microbiological culturing. This study is the first report of Brucella spp. DNA detection in cetaceans in the state of Pernambuco, and it highlights the importance of conducting systematic monitoring for the presence of Brucella infection in marine mammals along the Brazilian coast, especially in the northeast region, where several cases have been reported.

Spatial and seasonal variations in surface water temperature and salinity in the Mexico‐Belize riverine estuary: Possible comfort conditions for manatees?

AbstractThe Mexican Caribbean and Belize are home to one of the largest populations of Caribbean manatees (Trichechus manatus manatus). However, the transboundary Hondo River estuary is less examined compared to the surrounding protected areas. This paper provides a quantitative description of the spatial and temporal variability in abiotic factors and manatee distribution throughout the Hondo River estuary, with monthly field measurements during 2018–2019. Simultaneously, visual observations and side‐scan sonar detection were implemented, with 84 manatee sightings reported (calves 11.9%, noncalves 88.1%). Heatmap and frequency analyses showed that most manatee sightings occurred at the riverine estuary limit, the confluences between the river and the bay into which it flows. The surface water temperature and salinity ranged 28°C ≤ T ≤ 32°C and 0.5 PSU ≤ S ≤ 4.5 PSU for ~72% of the manatees identified, potentially describing locally preferred conditions for manatees. During the regional mid‐summer drought, higher temperature (31.5°C), salinity (18 PSU), and estuary extent (17.6 km) were recorded, including the maximum peak of manatee sightings (~31%). The roles of these abiotic factors are discussed as tentative environmental comfort conditions for manatees that could reduce their energy and maintenance costs. The identification of preferred conditions could broaden perspectives on how manatees interact with their habitats.

Causes of Mortality for Endangered Antillean Manatees in Cuba

The Antillean manatee is categorized as endangered by the International Union for the Conservation of Nature primarily due to its low abundance. Further declines in abundance are expected due to a group of human related threats that include illegal hunting, fatal interactions with fishing gear, increasing watercraft traffic, and pollution. The nature of current threats is not well described for every critical population of manatees. In particular, threats to manatees have not been documented or evaluated in a systematic manner in coastal waters surrounding Cuba, which is a major reason why plans specifically addressing conservation of manatees in Cuba have not been implemented. To address this lack of information, we assessed patterns in various threats by reviewing reports of stranded (alive or dead) and captured manatees, with some reports being historical and others consistently available since 2001. For 94% of the contemporary cases, carcasses of dead animals were reported; the remainder (6%) involved live manatees and subsequent efforts to rescue and rehabilitate them. Documented causes of mortality included poaching (38%), entanglement in fishing gear (10%), deaths of dependent calves (2.5%), and boat collisions (2.5%). The cause of death for the remaining 47% of reports could not be determined. Mortalities were highest in areas with intensive commercial fishing effort, and mortalities in marine protected areas indicated a need for improved management. These initial findings provide the first estimates of the magnitude of mortality of manatees in Cuba and yield valuable insights into the causes of deaths. The existence of intense and poorly regulated fishing in certain areas, including protected areas, represents a potentially significant threat to manatees. The effects and management of this activity, especially in habitats that are critical for manatees, merit further attention.

Using Tetracycline to Evaluate Age Estimation in a Long‐Lived Aquatic Mammal

ABSTRACTAge 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.

Morphometric and structural analysis of Florida manatee spermatozoa.

Sperm characteristics, such as sperm morphology and sperm morphometry are important in assessing sperm quality. This is especially important for the management and conservation of endangered and exotic species, like the Florida manatee, where information of this nature is extremely limited. In this study, we fill this knowledge gap to better understand the reproductive physiology of Florida manatees by conducting the first extensive analysis of sperm morphometry and ultrastructure. Sperm were retrieved from the vas deferens of nine recently deceased Florida manatees. Computer‐aided sperm morphology analysis (CASMA) was used for morphometric analysis and laser‐scanning confocal microscopy and electron microscopy were used for structural and ultrastructural characterization. Our findings reveal new morphometric and structural data for the Florida manatee spermatozoon. Twelve morphometric features of Florida manatee sperm were quantified with some approximately 1.5–2 times larger than those previously reported. Ultrastructurally, the Florida manatee spermatozoon followed a mammalian structural pattern with an ovate‐shaped head, midpiece containing 84–90 mitochondria, and a flagellum. However, unique ultrastructural features were identified. Distinct, rectangular‐like enlargement of four outer dense fibers surrounding the axoneme was evident, which may provide additional tensile strength to counteract the forces on sperm transiting the female reproductive tract. Likewise, strong localization of F‐actin fibers within the midpiece may function to maintain sperm integrity within the female reproductive tract. These findings highlight the potential effects of sexual selective pressures on sperm size and structure in the Florida manatee and provide avenues for research on the occurrence of sperm competition in this species.