Morphological analysis of the digestive tract of Antillean manatee (Trichechus manatus manatus, Linnaeus, 1758) in northeast Brazil

Morphological studies of the digestive tract are relevant to know the biology and understand the eating habits to conserve species. Our objective was to analyze macroscopically and microscopically the digestive tract of Antillean manatee (Trichechus manatus manatus). Samples were collected from 20 animals found dead stranded on the coast of northeastern Brazil or that died during the rehabilitation process in captivity between July 1995 and March 2017. The macroscopic analysis of the gastrointestinal tract was carried out from the in loco monitoring of the two necropsies. For microscopic evaluation, tissue fragments were collected during necropsy, fixed with 10% buffered formaldehyde and subjected to routine histological processing, with 5 μm thick slices, and subsequently submitted to the Hematoxylin-Eosin staining method, the Verhoeff method, and the periodic acid-Schiff method. Macroscopically, neonates and adults have the same digestive tract structures, namely esophagus, stomach, duodenum, jejunum, ileum, cecum, colon, and rectum. The microscopic analysis demonstrated that the digestive tract is formed by four histological layers (mucosa, submucosa, muscularis, and serosa or adventitia). In the esophagus, esophageal glands are absent and there are elastic fibers in the submucosal layer and between the external muscle and adventitial layers. The stomach has a structure called the cardiac gland, which microscopically presents ontogenetic differences regarding the depth of the lining epithelium and the orderly distribution of cells along the gastric gland. In the duodenal ampulla and in the diverticula, duodenal glands were identified in the submucosa. The luminal portion of the mucous layer of the cecal ampulla, colon, and rectum is lined by keratinized stratified squamous epithelium. The digestive tract of the species Antillean manatee is similar to what has been reported for the order Sirenia

Searching for relations between manatee Trichechus manatus manatus calf strandings and environmental degradation in two Northeastern Brazil estuaries

Northeast Brazilian populations of the Antillean manatee are threatened by different causes, where the frequent stranding of calves is possibly an indirect result of anthropic environmental degradation. In this study we surveyed the spatial-temporal stranding patterns of newborn manatee calves at the coast of the state of Rio Grande do Norte and identified potential abiotic and anthropic determinants. To do so, we investigated changes in the mangrove cover and extension of salt evaporation ponds and shrimp farms along two estuaries, Apodi-Mossoró and Piranhas-Açu, during 1998 - 2018. The incidence of strandings increased throughout the study period, especially in Apodi- Mossoró, suggesting that the growing salt and shrimp farming industries are significant contributors to the observed mangrove deforestation. Thus, our findings suggest a correlation between manatee calf stranding patterns and environmental degradation from salt and shrimp production in two Northeast Brazilian estuaries

Density and abundance estimation of West Indian manatee, Trichechus manatus, between the states of Ceará and Piauí, Northeast Brazil, using active acoustics

The West Indian manatee is one of the most threatened species in Brazil. The species has currently a patchy distribution from the state of Alagoas to the state of Amapá. The difficulty of observing manatees, especially in estuarine waters, is a challenge for conservation. Therefore, it is necessary to use new methodologies and technologies to solve manatee detection problems in their natural habitats. The goal of this study was to use an active acoustic method of detection to estimate manatee density and abundance in the estuarine complex of the Timonha and Ubatuba rivers, between the states of Ceará and Piauí, northeast Brazil. Data collection was conducted from a wooden boat with an outboard motor using a side-scan sonar. Sonar images were collected along line transects in three regions within the study area. Manatee abundance was calculated using distance sampling (Distance 6.0 software). There were 1,396 transection lines that totaled 863.6 km traveled in the study area. The observed general encounter rate was 0.089 group detected per kilometer traveled. The best detection model was the hazard-rate with no adjustment terms, resulting in a detection probability of 33.7%, and an estimated density for the entire study area of 9.19 manatees per km2. Abundance of manatees in the estuary was estimated to be 37 animals (CV% = 30.2, 95% CI = 21 - 66). The methodology using side-scan sonar proposed here was successful in the detection of manatees in the study area and in defining parameters for its use to estimate the population size using the distance sampling method. This study provides an estimate of manatee density and abundance in a key estuarine system along the northeast coast of Brazil, which can serve as a baseline for future studies and aid in the development of conservation strategies for the species. This is the first time this methodological approach has been used for manatee detection and abundance estimation in Brazil. We recommend the use of side-scan sonar in future West Indian manatee research

Perceptions on the distribution, threats, strandings, and conservation of the Antillean manatee (Trichechus manatus manatus) in the Río Dulce National Park, Izabal, Guatemala

The Antillean manatee in Guatemala faces multiple threats resulting from habitat loss and human interactions such as motorboat collisions and poaching. While some conservation efforts have been initiated in Río Dulce National Park (RDNP), there is a lack of studies examining the current perceptions of threats to the species. This knowledge gap may hinder the development of effective conservation strategies that consider both the species and local communities. Our objective was to analyze the perceptions of key local stakeholders concerning the Antillean manatee, including its distribution, threats, attention to strandings, and the current status of conservation in the protected area of RDNP. From July to October 2019, we conducted 50 semi-structured interviews with technicians and river users, such as fishermen and boat captains. Additionally, we held two workshops: one aimed at developing a participatory mapping exercise and another to validate the information. Each workshop was divided into two groups: one for technicians and another for river users. A total of 68 people participated in the workshops, the majority of respondents were male (n = 47), ranging in age from 19 to 71, and predominantly local to the area. Their activities in the river included fishing, biological monitoring, transportation, and providing tourism services. Perceived threats to the Antillean manatee included motorboat collisions, poaching, bycatch, habitat degradation, and water pollution. The focus groups also identified key observations, such as mother-calf sightings, specific areas of risk for manatee-boat collisions, areas with a higher presence of aquatic vegetation, and additional threats such as habitat degradation and poaching. Our results demonstrate that stakeholders possess a fundamental understanding of the manatee, its threats, and its distribution. They also highlight a noticeable lack of knowledge, specifically regarding the attention given to manatee strandings. It is recommended that conservation strategies include environmental education adapted to local conditions, as well as the promotion of manatee studies and their dissemination at the local level, including attention to strandings in the area

Oral cleft in an Amazonian manatee (Trichechus inunguis) (Mammalia, Sirenia)

Since 1976, Amazonian manatees have been examined either alive or through necropsies as part of a long-term program to rescue and rehabilitate orphan manatee calves whose mothers were either victims of illegal hunting or accidental catch in fishing nets in the Brazilian Amazon region. Rescued manatees have been found to have several types of diseases, but to our knowledge, there is no record of a congenital anomaly of the face, known as an oral cleft, in Amazonian manatees. In this paper, we report the occurrence of an oral cleft in an Amazonian manatee calf, describing the clinical evaluation and discussing the potential causes

Accomplishments and challenges of the research on Antillean manatee: A bibliometric analysis

The Antillean manatee (Trichechus manatus manatus) is an endangered subspecies of the West Indian manatee inhabiting countries of South America, Meso America and the Caribbean. Basic and applied research is necessary to inform management plans for the effective recovery of this subspecies. The purpose of this study was to systematically review literature regarding Antillean manatees, without restriction of the research topic. Article selection and screening process are described. Our final database consisted of 456 publications, of which peer-reviewed literature (articles, reviews, and notes in research journals) represent the most important type (63.4%), followed by BSc, MSc, and PhD theses (28.1%). Most of the research (70%) was conducted on wild manatees, 21,5% under human care conditions, and the rest a combination of both; the most common topics of study were ‘ecology’, ‘conservation’, ‘morphology, anatomy and physiology’, and ‘behavior’. The literature on Antillean manatee has expanded significantly over the last two decades across the region, with most of the research published in just the last five (25.4%) to 10 (44.6%) years. Most of the published work has been by Brazilian, Mexican, and Colombian researchers. However, an important amount of research remains as theses in Portuguese or Spanish limiting the dissemination of results. Relevant limitations for research and publication in Latin American countries may have an impact on the published literature on Antillean manatees, including scarce funding, poor facilities, language-related difficulties, and lack of a culture of publication. Avenues to melt scientific barriers may include increasing governmental investment on research, strengthening international networks, and improving the support to publish in high-impact journals