Manatee Trichechus manatus latirostris calf mortality in Florida: a retrospective review of pathology data from 2009-2017

High maternal investment and extended inter-calving intervals in Florida manatees Trichechus manatus latirostris make calf survivorship critical to overall population growth. However, detailed patterns of causes of mortality in calves have not been reported and state agency statistics report portions of perinatal mortality based on body length rather than actual cause of death (COD). The objectives of this study were to categorize COD based on necropsy data and geographical location in Florida for 1209 manatee calf carcasses (<236 cm total length) examined between January 2009 and December 2017 and to describe factors contributing to calf mortality. Results indicated COD was attributed to natural causes (47%, n = 573), cold stress syndrome (38%, n = 457), watercraft injury (13%, n = 155), or other human-related causes (2%, n = 24). Natural causes were the leading COD for small calves <151 cm, with death due to stillbirth or dystocia most frequent (48%, n = 273/573). Enteric trematodiasis contributed to a large proportion of deaths from natural causes in large calves within the southwest region of Florida, with an increasing annual trend. Brevetoxicosis contributed substantially to natural causes within the southwest region exclusively and was commonly comorbid with enteric trematodiasis. Cold stress syndrome was the leading cause of death for large calves (151-235 cm), with the Atlantic region having the highest proportion of cases. Watercraft injury was a sustained threat to large calves, especially within the southwest region. This report provides details on specific health threats and patterns of mortality among manatee calves.

A Necropsy Study of Disease and Comorbidity Trends in Morbidity and Mortality in the Koala (Phascolarctos cinereus) in South-East Queensland, Australia

Koalas are an iconic Australian marsupial undergoing precipitous population reduction in South-East Queensland from complex interacting threats. To investigate the causes of death and the interaction of comorbidities with demography in South-East Queensland koalas, a large scale, high-throughput prospective necropsy survey was conducted spanning 2013–2016. During this period, 519 necropsies were conducted in 155 young/subadult koalas, 235 mature, 119 old koalas and 10 of unknown age. Similar numbers of males and females were assessed. Trauma and infectious disease at were the most common single diagnoses. However, comorbidity was frequent, including multicentric infection or infectious disease in combination with trauma or senescence. Female koalas had proportionally more reproductive chlamydiosis compared to males in which the ocular and urinary systems were more commonly affected. Comorbidity and disease were strongly associated with poor body condition, and trauma was associated with good body condition. Animals affected by motor vehicle trauma were often in better body condition than those affected by animal attack, tree fall or other causes of trauma. This study identified a higher frequency of infections and comorbidity then previously reported, confirming the complex nature of interacting threats to the koala population.

Cold-related Florida manatee mortality in relation to air and water temperatures

Many tropical and subtropical species are sensitive to sudden temperature changes, especially drops in temperature. During winters 2009–2010 and 2010–2011, unusually cold temperatures occurred in many parts of Florida, USA, resulting in increased mortality of Florida manatees, sea turtles, fish, corals, and other species. The Florida manatee, in particular, is highly susceptible to cold stress and death when water temperatures drop below 20°C. We sought to characterize the magnitude and timing of reports of cold-related manatee carcasses in relation to fluctuations in water and air temperatures in central-east and central-west Florida during the six winters from 2008 to 2014. We used a generalized linear model to predict counts of manatee carcasses with a cold-related cause of death reported over 7-day bins in relation to various short-term (two weeks or less) and cumulative (incrementally summed from the start of the winter) heating-degree-day effects (HDD; < 20°C) and a categorical winter variable. Using water temperature data, the top-ranked model in both regions included a short-term temperature effect (14-day HDD sum) that preceded increases in reports of cold-related manatee carcasses by 7 days. Cumulative exposure to cold weather over the winter amplified effects on mortality in the central-east region. Quantifying the relationship between cold events and manatee mortality helps us prepare for rescue and salvage operations when extremely cold weather is forecast. This is especially important because anticipated loss or degradation of warm-water refuges due to human activities and sea level rise could potentially impact the manatee population in the future. These methods could also be applied to other species susceptible to cold-related mortality.

COASTAL HABITAT CHANGE AND MARINE MEGAFAUNA BEHAVIOR: FLORIDA MANATEES ENCOUNTERING REDUCED FOOD PROVISIONS IN A PROMINENT WINTER REFUGE

A decline in submerged aquatic vegetation (SAV) within Florida's spring-fed, thermal refuges raises questions about how these systems support winter foraging of Florida manatees (Trichechus manatus latirostris). We analyzed telemetry data for 12 manatees over seven years to assess their use of Kings Bay, a winter refuge with diminished SAV. After accounting for the effect of water temperature, we hypothesized that the number of trips out of Kings Bay would increase and the time wintering manatees spent in Kings Bay would decrease. Trips out of and into Kings Bay also were compared to assess potential influences on exiting or entering. There were no detectable differences in the number of trips out of the bay or overall time manatees spent in Kings Bay across winters. The percentage of time water temperatures were below 20°C was the single best predictor of increased time spent in Kings Bay. Trips out of Kings Bay were more likely to occur after 12:00 h and during a high but ebbing tide, compared to trips into the bay. Nine manatees tracked for longer than 75 days in winter spent 7-57% of their time in the Gulf of Mexico, and three of these manatees spent 7-65% of the winter >80 km from the mouth of Kings Bay. Results suggest the low amount of SAV in Kings Bay does not obviate its use by manatees, though there are likely tradeoffs for manatees regularly foraging elsewhere. Accounting for movements of Florida manatees through a network of habitats may improve management strategies and facilitate desirable conservation outcomes.

Parasite fauna of wild Antillean manatees (Trichechus manatus manatus) of the Andean Region, Colombia

BACKGROUND

Antillean manatees (Trichechus manatus manatus) are large herbivorous aquatic mammals living in limited areas of South, Central and North America. As with other aquatic mammals, Antillean manatees can be infected by a variety of protozoan and metazoan parasites, some of them with zoonotic potential, which affect not only their welfare but also population health status. Therefore, we conducted the first epidemiological survey in Colombian free-ranging Antillean manatees to estimate their actual gastrointestinal parasite status.

RESULTS

In total, 69 faecal samples were collected from free-ranging individual manatees during ecology field studies in the rivers Carare and San Juan and in two associated wetlands in the Andean region of Colombia. Parasite diversity encompassed six different endoparasite species. The highest prevalence was found for protozoan infections with Eimeria nodulosa (47.8%) and Eimeria manatus-like species (type A, B; 43.4%), followed by Entamoeba sp. (14.49%) and Giardia sp. (1.4%) infections. In addition, infections with the trematode Chiorchis fabaceus were detected at a high prevalence (33.3%). Molecular characterization of sirenian Eimeria species led to the distinction of three species, E. nodulosa and two E. manatus-like species (type A, B). Phylogenetic analyses indicated a host-specific adaptation of sirenian Eimeria species as previously reported for Eimeria species from other mammalian hosts.

CONCLUSIONS

This study provides the first record of Antillean manatee infection with Giardia and Entamoeba species in Colombia, representing two important anthropozoonotic parasite genera. This survey should serve as a baseline investigation for future monitoring on parasitic zoonoses in this mammal and encourage for investigations on their impact on both public health and wild manatee welfare.

Heat flux in manatees: an individual matter and a novel approach to assess and monitor the thermal state of Florida manatees (Trichechus manatus latirostris)

Florida manatees (Trichechus manatus latirostris) possess an unusual suite of adaptations to accommodate both a fully aquatic lifestyle and an herbivorous diet, including a low metabolic rate and a very limited thermoneutral zone. Their relatively high lower critical temperature of around 20 °C suggests strong sensitivity to cold, thereby limiting their distribution to tropical and subtropical waters. "Cold stress syndrome" affects and kills Florida manatees every year during intense or prolonged cold weather, posing one of the major threats to manatees. However, knowledge regarding manatee thermoregulation is sparse, but essential for effective conservation and management of this threatened species. We measured heat flux in two captive Florida manatees at multiple times of the year, at 41 sites distributed across the entire body surface of each manatee. Heat flux differed significantly between individuals, and among body sites and times of the year. The pectoral flippers and axillae were identified as areas with highest heat exchange. Despite exposure to constant water temperature throughout the year, the manatees in this study had significantly lower heat flux in winter than in summer. We used the measured heat flux values to calculate total heat dissipation in individual manatees. The values estimated this way correspond well with the low metabolic rates estimated in previous studies, confirming the reliability of our novel approach. Our method provides simple and useful options for enhancing manatee welfare by monitoring the animals' thermal state during potentially stressful activities such as during medical treatment, capture restraints and transportation.

Fishery gear interactions from stranded bottlenose dolphins, Florida manatees and sea turtles in Florida, U.S.A

Documenting the extent of fishery gear interactions is critical to wildlife conservation efforts, especially for reducing entanglements and ingestion. This study summarizes fishery gear interactions involving common bottlenose dolphins (Tursiops truncatus truncatus), Florida manatees (Trichechus manatus latirostris) and sea turtles: loggerhead (Caretta caretta), green turtle (Chelonia mydas), leatherback (Dermochelys coriacea), hawksbill (Eretmochelys imbricata), Kemp's ridley (Lepidochelys kempii), and olive ridley (Lepidochelys olivacea) stranding in Florida waters during 1997-2009. Fishery gear interactions for all species combined were 75.3% hook and line, 18.2% trap pot gear, 4.8% fishing nets, and 1.7% in multiple gears. Total reported fishery gear cases increased over time for dolphins (p<0.05), manatees (p<0.01), loggerheads (p<0.05) and green sea turtles (p<0.05). The proportion of net interaction strandings relative to total strandings for loggerhead sea turtles increased (p<0.05). Additionally, life stage and sex patterns were examined, fishery gear interaction hotspots were identified and generalized linear regression modeling was conducted.

Diagnostic stages of the parasites of the Florida manatee, Trichechus manatus latirostris

Limited information is available on diagnostic stages of parasites in Florida manatees (Trichechus manatus latirostris). We examined 67 fecal samples from captive and wild manatees to define the diagnostic stages of the parasite fauna known to occur in Florida manatees. Parasite eggs were freshly extracted ex utero from identified mature helminths and subsequently characterized, illustrated, and matched to those isolated from fecal samples. In addition, coccidian oocysts in the fecal samples were identified. These diagnostic stages included eggs from 5 species of trematodes (Chiorchis fabaceus, Chiorchis groschafti, Pulmonicola cochleotrema, Moniligerum blairi, and Nudacotyle undicola), 1 nematode (Heterocheilus tunicatus), and oocysts of 2 coccidians (Eimeria manatus and Eimeria nodulosa).

Sex, scarring, and stress: understanding seasonal costs in a cryptic marine mammal

We investigated variation in adrenal activity in the dugong, a vulnerable cryptic marine mammal species, in a population inhabiting the lower thermal limit of their range. We sampled 319 live wild dugongs and examined faecal glucocorticoid (fGC) concentrations in relationship to sex, reproductive state (immature, sexually mature, or pregnant), and season, as well as associations with body condition, male-induced aggressive conspecific interactions, and environmental temperature. Physiological validations with apparently healthy and unhealthy animals indicated that fGC levels reliably reflect adrenal activation in dugongs. Glucocorticoid levels and body condition varied seasonally, with individuals expressing lowest fGC levels and an improving body condition over summer and autumn. Best body condition was observed in winter, which may have enhanced the ability of the animals to cope with thermal and nutritional challenges and helped to sustain the subsequent costs of reproduction (including mating activity in spring). Immature dugongs, especially those recently estranged from their mothers, may be particularly vulnerable to stress during winter, and also at risk of injury from adult conspecifics. During the spring mating period, mature and sexually active males with large erupted tusks had high fGC and poorer body condition compared with all dugongs, except pregnant females, in all other seasons. This finding was consistent with high levels of body scarring on adults of both sexes, resulting from agonistic behaviour by mature males. Competitive reproductive behaviour, inherent in a promiscuous mating system, may have stressful consequences for male dugongs, especially given that strenuous mating activity follows unfavourable thermal and nutritional conditions. Overall, fGC levels appear to be a good proxy for stressors in dugongs associated with season and/or temperature, intra-specific aggression, and pregnancy, but not lactation and/or maternal care. Understanding baseline fGC levels will allow wildlife managers to identify additional and/or unusual stressors that may threaten wild dugong populations.

Improving conservation of Florida manatees (Trichechus manatus latirostris): conceptualization and contributions toward a regional warm-water network management strategy for sustainable winter habitat

We used southwestern Florida as a case study to lay the groundwork for an intended and organized decision-making process for managing warm-water habitat needed by endangered manatees to survive winters in Florida. Scientists and managers have prioritized (a) projecting how the network of warm-water sites will change over the next 50 years as warmed industrial discharges may expire and as flows of natural springs are reduced through redirection of water for human uses, and (b) mitigating such changes to prevent undue consequences to manatees. Given the complexities introduced by manatee ecology; agency organizational structure; shifting public demands; fluctuating resource availability; and managing within interacting cultural, social, political, and environmental contexts, it was clear that a structured decision process was needed. To help promote such a process, we collected information relevant to future decisions including maps of known and suspected warm-water sites and prototyped a characterization of sites and networks. We propose steps that would lead to models that might serve as core tools in manatee/warm-water decision-making, and we summarized topics relevant for informed decision-making (e.g., manatee spatial cognition, risk of cold-stress morbidity and mortality, and human dimensions). A major impetus behind this effort is to ensure proactively that robust modeling tools are available well in advance of the anticipated need for a critical management decision.

Activities and social interactions in captive Antillean manatees in Mexico

Behavioural research in endangered manatees is essential for successful conservation management. We examined the activities and social interactions of a captive group of Antillean manatees located in the Dolphin Discovery Park in Mexico. The group studied was composed of two adults, one subadult and one calf. We determined activity patterns and space use of the manatees in a natural water pool over a daytime period and a night-time period. The behavioural strategies of the manatees included (1) during the day, mainly foraging, feeding, and remaining inactive, and (2) evening activities were divided among social interaction, environment exploration, and resting activities. All the behaviour patterns of the captive manatees seemed to be influenced by the feeding schedule during the day. The number of contacts between manatees increased strongly at night, each individual having a preferred partner for social interaction. The cow-calf dyad showed the highest intensity of contacts, whereas subadults showed the lowest. The relationships observed among individuals reveal a higher social activity than previously described in Antillean manatees.

Carbon and nitrogen stable isotope turnover rates and diet-tissue discrimination in Florida manatees (Trichechus manatus latirostris)

The Florida manatee (Trichechus manatus latirostris) is a herbivorous marine mammal that occupies freshwater, estuarine and marine habitats. Despite being considered endangered, relatively little is known about its feeding ecology. The present study expands on previous work on manatee feeding ecology by providing critical baseline parameters for accurate isotopic data interpretation. Stable carbon and nitrogen isotope ratios were examined over a period of more than 1 year in the epidermis of rescued Florida manatees that were transitioning from a diet of aquatic forage to terrestrial forage (lettuce). The mean half-life for (13)C turnover was 53 and 59 days for skin from manatees rescued from coastal and riverine regions, respectively. The mean half-life for (15)N turnover was 27 and 58 days, respectively. Because of these slow turnover rates, carbon and nitrogen stable isotope analysis in manatee epidermis is useful in summarizing average dietary intake over a long period of time rather than assessing recent diet. In addition to turnover rate, a diet-tissue discrimination value of 2.8 per thousand for (13)C was calculated for long-term captive manatees on a lettuce diet. Determining both turnover rate and diet-tissue discrimination is essential in order to accurately interpret stable isotope data.

Distribution and exploitation of manatees in Sierra Leone

West African manatees are believed to be declining over much of their range, including in Sierra Leone. They are nominally protected there, but they are traditionally caught and eaten because of their delicious meat and also because they are considered as pests by rice growers and fishermen. The authors' surveys in 1986–1987 showed that manatees are still widely distributed in coastal districts of the country, but that they are being regularly caught in some places, at levels that may not be sustainable. Much more needs to be known to guide appropriate action to ensure that the manatee remains a part of Sierra Leone's wildlife. It is encouraging that one of the authors has begun, under the government Fisheries Division, to implement a manatee research programme.

Embarcações motorizadas: uma ameaça aos peixes-boi marinhos (Trichechus manatus) no Brasil

O aumento do tráfego de embarcações motorizadas em áreas utilizadas para alimentação, descanso e reprodução pelos peixes-boi marinhos tem não só afugentado estes animais, mas resultado em potenciais casos de colisões. Este trabalho tem como objetivo relatar casos de interações entre embarcações motorizadas e peixes-boi marinhos (Trichechus manatus) no litoral Nordeste do Brasil. As interações ocorreram nos Estados do Ceará, Paraíba e Sergipe com três espécimes, sendo um destes com quatro registros. Foram observados transtornos clínicos como edema da região frontal, proptose ocular, emagrecimento e múltiplos cortes ao longo do corpo. Sendo assim, o aumento do tráfego de embarcações, e a falta de normativas e de fiscalização que assegurem a efetiva proteção de determinadas áreas, representam um risco direto para a conservação dos peixes-boi marinhos no litoral Nordeste do Brasil.

ELECTROCARDIOGRAPHY IN TWO SUBSPECIES OF MANATEE (TRICHECHUS MANATUS LATIROSTRIS AND T. M. MANATUS)

Electrocardiographic (ECG) measurements were recorded in two subspecies of awake, apparently healthy, wild manatees (Trichechus manatus latirostris and T. m. manatus) undergoing routine field examinations in Florida and Belize. Six unsedated juveniles (dependent and independent calves) and 6 adults were restrained in ventral recumbency for ECG measurements. Six lead ECGs were recorded for all manatees and the following parameters were determined: heart rate and rhythm; P, QRS, and T wave morphology, amplitude, and duration; and mean electrical axis (MEA). Statistical differences using a t-test for equality of means were determined. No statistical difference was seen based on sex or subspecies of manatees in the above measured criteria. Statistical differences existed in heart rate (P = 0.047), P wave duration (P = 0.019), PR interval (P = 0.025), and MEA (P = 0.021) between adult manatees and calves. Our findings revealed normal sinus rhythms, no detectable arrhythmias, prolonged PR and QT intervals, prolonged P wave duration, and small R wave amplitude as compared with cetacea and other marine mammals. This paper documents the techniques for and baseline recordings of ECGs in juvenile and adult free-living manatees. It also demonstrates that continual assessment of cardiac electrical activity in the awake manatee can be completed and can be used to aid veterinarians and biologists in routine health assessment, during procedures, and in detecting the presence of cardiac disease or dysfunction.

METHODS USED DURING GROSS NECROPSY TO DETERMINE WATERCRAFT-RELATED MORTALITY IN THE FLORIDA MANATEE (TRICHECHUS MANATUS LATIROSTRIS)

Between 1993 and 2003, 713 (24%) of 2,940 dead Florida manatees (Trichechus manatus latirostris) recovered from Florida waters and examined were killed by watercraft-induced trauma. It was determined that this mortality was the result of watercraft trauma because the external wound patterns and the internal lesions seen during gross necropsy are recognizable and diagnostic. This study documents the methods used in determining watercraft-related mortality during gross necropsy and explains why these findings are diagnostic. Watercraft can inflict sharp- and blunt-force trauma to manatees, and both types of trauma can lead to mortality. This mortality may be a direct result of the sharp and blunt forces or from the chronic effects resulting from either force. In cases in which death is caused by a chronic wound-related complication, the original incident is usually considered to be the cause of death. Once a cause of death is determined, it is recorded in an extensive database and is used by Federal and state managers in developing strategies for the conservation of the manatee. Common sequelae to watercraft-induced trauma include skin lesions, torn muscles, fractured and luxated bones, lacerated internal organs, hemothorax, pneumothorax, pyothorax, hydrothorax, abdominal hemorrhage and ascites, and pyoperitoneum.

Application of Fracture Mechanics to Failure in Manatee Rib Bone

Background. The Florida manatee (Trichechus manatus latirostris) is listed as endangered by the U.S. Department of the Interior. Manatee ribs have different microstructure from the compact bone of other mammals. Biomechanical properties of the manatee ribs need to be better understood. Fracture toughness (KC) has been shown to be a good index to assess the mechanical performance of bone. Quantitative fractography can be used in concert with fracture mechanics equations to identify fracture initiating defects∕cracks and to calculate the fracture toughness of bone materials. Method of approach. Fractography is a standard technique for analyzing fracture behavior of brittle and quasi-brittle materials. Manatee ribs are highly mineralized and fracture in a manner similar to quasi-brittle materials. Therefore, quantitative fractography was applied to determine the fracture toughness of manatee ribs. Results. Average fracture toughness values of small flexure specimens from six different sizes of manatees ranged from 1.3to2.6MPa(m)1∕2. Scanning electron microscope (SEM) images show most of the fracture origins were at openings for blood vessels and interlayer spaces. Conclusions. Quantitative fractography and fracture mechanics can be combined to estimate the fracture toughness of the material in manatee rib bone. Fracture toughness of subadult and calf manatees appears to increase as the size of the manatee increases. Average fracture toughness of the manatee rib bone materials is less than the transverse fracture toughness of human and bovine tibia and femur.

Vascular adaptations for heat conservation in the tail of Florida manatees (Trichechus manatus latirostris)

Although Florida manatees (Trichechus manatus latirostris) have relatively low basal metabolic rates for aquatic mammals of their size, they maintain normal mammalian core temperatures. We describe vascular structures in the manatee tail that permit countercurrent heat exchange (CCHE) to conserve thermal energy. Approximately 1000 arteries juxtaposed to 2000 veins are found at the cranial end of the caudal vascular bundle (CVB); these numbers decrease caudally, but the 1:2 ratio of arteries to veins persists. Arterial walls are relatively thin when compared to those previously described in vascular countercurrent heat exchangers in cetaceans. It is assumed that CCHE in the CVB helps manatees to maintain core temperatures. Activity in warm water, however, mandates a mechanism that prevents elevated core temperatures. The tail could transfer heat to the environment if arterial blood delivered to the skin were warmer than the surrounding water; unfortunately, CCHE prevents this heat transfer. We describe deep caudal veins that provide a collateral venous return from the tail. This return, which is physically outside the CVB, reduces the venous volume within the bundle and allows arterial expansion and increased arterial supply to the skin, and thus helps prevent elevated core temperatures.

Comparison of lipids in selected tissues of the Florida manatee (Order Sirenia) and bottlenose dolphin (Order Cetacea; Suborder Odontoceti)

The position, porosity and oil-filled nature of the zygomatic process of the squamosal bone (ZPSB) of the Florida manatee, Trichechus manatus latirostris, suggest that it may have a similar sound conduction function to that of the intramandibular fat body (IMFB) of the bottlenose dolphin, Tursiops truncatus, and other odontocetes. To examine this possibility we determined the lipid composition of the ZPSB and adipose tissue from the dorsal part of the head region of the Florida manatee, and compared it to that of the dolphin IMFB and melon (another fatty area implicated in sound conduction in odontocetes). Lipids from manatee ZPSB and from adipose tissue were composed almost entirely of triacylglycerols. The most abundant fatty acids of the ZPSB were 18:1, 16:0, 14:0 and 16:1. The major fatty acids of the adipose tissue in the head were the four mentioned above, along with 12:0 and 18:0. Manatee samples did not contain isovaleric acid (iso-5:0), which was found in the bottlenose dolphin IMFB and melon, and has been related to sound conduction in dolphins and some other odontocetes. Thus, if manatee tissues are capable of sound conduction, and this process does occur through the ZPSB, a somewhat different suite of lipid components must support this function.

The influence of sex and reproductive state on diet preference in four terrestrial mammals of the French Guianan rain forest

The diets of males and pregnant and nonpregnant females were studied in four French Guianan mammal species, three rodents and one artiodactyl, illustrating a gradient of size, mass, and gestation, and thus of energy and protein requirements. In the rodents (Oryzomys capito, Proechimys cuvieri, Dasyprocta leporina), males were more frugivorous than females, whereas the reverse was the case in the artiodactyl (Tayassu tajacu). For all species, males ate the most pulp, while pregnant females focused on seeds or animal matter. Nevertheless, males and females appeared to be opportunistic foragers, with similar feeding strategies throughout the year. A comparative analysis of stomach contents showed that the diets of males and nonpregnant females were quite comparable, while significant differences occurred in gravid females (especially of the two smallest species). Intra-individual differences gradually decreased from O. capito to T. tajacu, possibly as a result of closer male and female cohabitation as well as lower relative energy and protein requirements for pregnant females of the larger species. Finally, for the two smallest species, reproductive activity was correlated with seed and (or) animal matter intake.

Structure and function of the gastrointestinal tract of the Florida manatee, Trichechus manatus latirostris

BACKGROUND

The Florida manatee, Trichechus manatus latirostris (Sirenia: Trichechidae), is the largest herbivorous marine mammal. Previously, components of the gastrointestinal (GI) tract of the species have been described, but no comprehensive descriptions of the gross and microscopic anatomy existed. This study integrates function and structure of the entire Florida manatee GI tract.

METHODS

The GI tracts of several recently dead Florida manatees were examined from the following viewpoints: gross anatomical studies of preserved and unpreserved specimens, histology and histochemistry, and ultrastructure.

RESULTS

The manatee GI tract has an enlarged hindgut, as do other nonruminant herbivores (i.e., hindgut digesters such as horses), but it also has important adaptations not seen in most other mammals. These structural adaptations include a discrete accessory digestive gland (the cardiac gland), submucosal mucous glands along the greater curvature of the stomach, and unkeratinized, stratified squamous epithelial cells overlying the glandular mucosae of the pyloric antrum, midgut cecum, colon, and rectum.

CONCLUSIONS

The adaptations described above may relate to osmoregulation as well as to herbivory. The Florida manatee GI tract is most similar to those of other members of the Order Sirenia and to that of the herbivorous green sea turtle (Chelonia mydas), but it also shows superficial similarities to those of phylogenetically close Orders, the Proboscidea and Hyracoidea. The immense size of both the manatee and its large intestine suggests that, relative to smaller hindgut digesters, manatees have a slow rate of passage of digesta and efficient breakdown of fibrous plant material.