Latin American Journal of Aquatic Mammals

Influence of sex and home range on released Antillean manatees’ behavior in Brazil

Helena G. do Val — 2024-04-28

The Antillean manatee is a threatened aquatic mammal subspecies which inhabits the northern and northeastern Brazilian coasts and estuarine areas. In this study we analyzed behavior data from rehabilitated and released manatees, to evaluate if sex and home range affect behavior richness and activity budget. Behavioral data from 29 manatees (15 females and 14 males) of northeastern Brazil was analyzed from 2006 to 2018. The animals were monitored by trained staff, who followed the animals using satellite and VHF telemetry systems. Six behavior states and 17 behavior events were recorded. The data was analyzed using GLM, ANOVA, and regression statistical tests. Behavior richness varied from three to 14 and activity budget indicated that individuals spent more time engaged in behaviors such as moving slowly and feeding in the bottom of the water body, but neither behavior richness nor activity budget were affected by sex. Behavior richness related to home range varied from five to 14 behaviors. Behavior richness and the activity budget for two social behaviors events - touch and interaction with wild manatees - were positively influenced by home range size, highlighting the importance of the use of space on behavior expression in manatees.

Proximity to freshwater and seagrass availability mediate the impacts of climate change on the distribution of the West Indian manatee

Emma Deeks — 2024-04-28

How climate change alters persistence and distribution of endangered species is an urgent question in current ecological research. However, many species distribution models do not consider consumers in the context of their resources. The distribution and survival of the West Indian manatee (Trichechus manatus), listed as a Vulnerable species on the IUCN Red List, critically depend on seagrass resources and freshwater sources for drinking. We parameterized Maxent models with Bio-ORACLE environmental layers, freshwater proximity data, and modelled seagrass distance layers, to determine manatee and seagrass distributions under future climate change scenarios. We used two plausible IPCC Representative Concentration Pathways (RCP45 and RCP26, respectively) for the year 2050. The model fits had high accuracies and predicted a marked decline in seagrass coverage (RCP26: -1.9%, RCP45: -6%), coinciding with declines in manatee ranges (RCP26: -9%, RCP45: -11.8%). We also found that over 94% of the projected manatee distribution for all scenarios fell within the seagrass distribution. The analysis showed a decline in seagrass coverage to significantly impact manatee distributions, since the distance to seagrass ecological layer contributed significantly to manatee distributions, along with distance to freshwater sources. Our findings suggest that manatees will lose substantial range due to future climate change, but the extent and direction of this change will be mediated by the degree of warming and its impact on the resources manatees depend on.

Conservation challenges and emerging threats to the West Indian manatee (Trichechus manatus) in Florida and Puerto Rico

Aarin Conrad Allen — 2024-04-28

Sirenians are experiencing unprecedented anthropogenic threats around the globe due to habitat destruction, interaction with fisheries, collisions with watercrafts, and climate change. Although the West Indian manatee (Trichechus manatus) has been protected by law for the past five decades, significant threats persist in the United States. In 2017, the US Fish and Wildlife Service (USFWS) downlisted the West Indian manatee from Endangered to Threatened under the Endangered Species Act of 1973 (ESA). Here, we provide an overview of the current conservation status of manatees in US waters, particularly in Florida and Puerto Rico. In recent years, there has been a marked increase in manatee mortalities in the US. The sources of these mortalities are relatively well known, particularly collisions with watercrafts. However, other sources have recently emerged and constitute threats of increasing concern, particularly resource depletion due to seagrass loss and emerging diseases. Recommendations for future research are proposed to improve our understanding of the magnitude of the threats affecting manatees in the US, and support management decisions and conservation actions.

Quantifying minimum survey effort to reliably detect Amazonian manatees using an unoccupied aerial vehicle (UAV) at an ex situ soft-release site

Sarah Farinelli — 2024-04-28

Detection of many threatened aquatic mammals, such as manatees (Trichechus spp.), using traditional visual observation methods is associated with high uncertainty due to their low surfacing times, cryptic behaviors, and the environmental heterogeneity of their habitats. Rapid advancements in technology provide an opportunity to address these challenges. In this study, we aimed to quantify survey effort of unoccupied aerial vehicles (UAVs) for detecting the Vulnerable Amazonian manatee (T. inunguis). Using a closed population of manatees that is being rehabilitated within a lake at the Rainforest Awareness, Rescue, and Education Center in Iquitos, Peru, we calculated the number of repeat surveys needed to detect at least one individual with 95% (n = 3.10) and 99% (n = 4.76) confidence. We used both generalized linear mixed-effect models and Bayesian single-species and single-season detection models to determine the effects of the environment (water depth, water transparency, cloud cover, wind speed), time of day, and behavior (breathing, foraging, milling) on the time-to-detection and detection probability, respectively. Both models indicated a significant interaction between water depth and water transparency, causing an increase in the time-to-detection (β = 0.032; 95% CI = 0.028, 0.037) and a decrease in the probability of detecting manatees (α = -0.65; 95% CI = -1.3, -0.007), which was calculated to be 0.62 (95% CI = 0.23, 0.94). Due to the similarities between the lake and in situ habitats, the results of this study could be used to design in situ UAV survey protocols for Amazonian manatees or other difficult-to-detect freshwater aquatic mammals and to monitor ex situ animals pre-and post-release, which should ultimately contribute to a better understanding of their spatial ecology and facilitate data-driven conservation efforts.

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

Mildred Fabiola Corona-Figueroa — 2024-04-28

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.

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

Rebeca Taines do Nascimento Pinheiro — 2024-04-28

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.

Antillean manatee (Trichechus manatus manatus) occurrence and grazing spots in three protected areas of Costa Rica

Priscilla Cubero-Pardo — 2024-04-28

The Antillean manatee is a poorly studied marine mammal in Costa Rica. Its distribution covers the entire Caribbean coast, but sighting reports are scarce. This research was conducted in three protected areas (PA) where the species is primarily observed. The objectives were to determine the density patterns of sightings and grazing spots; to explore the relationship between grazing spots and sightings with geographic and temporal variables, for PA separately; to study the frequency of sightings and grazing spots according to season, month, and period of the day, for PA together; and to determine the pertinence of using a marine ecology application MarEco to register manatee sightings by the public. Data on manatee sightings and grazing spots gathered with the MarEco app, under a citizen science mechanism, were complemented with data obtained by the Tortuguero Conservation Area Administration (TCAA) through other means. The number of sighting records registered through MarEco during nine months was alike to the number of records reported to the TCAA over six years in two of the PA studied. The areas with the highest density of grazing spots and sightings matched with studies conducted 10 to 20 years ago. In two of the PA, sightings were most often associated with the rainy season, while fresh grazing spots were specially counted from 6:00 h to 8:59 h. The results suggest that manatees exhibit high site fidelity in the three PA, that their increased presence during the rainy season is likely due to increased availability of food, and that they perform feeding activity predominantly at night.

Stranding reports of the Antillean manatee in the middle Magdalena Basin, Colombia 2011 to 2023

Gloria Katerin Arévalo-González — 2024-04-28

The aim of this study was to conduct an analysis of reported events concerning Antillean manatee (Trichechus manatus manatus) strandings in the middle Magdalena Basin region of Colombia from January 2011 to December 2023. To achieve this, a literature search was conducted in newspapers, news broadcasts, as well as gray and published reports, complemented by interviews and workshops with various governmental and non-governmental organizations. This search resulted in reliable information regarding past experiences involving stranded manatees over the years. Cases attended to by the environmental authority and its partners were also considered. Forty-four stranding events were recorded, with 34 deaths and 10 live manatees. Of the cases discovered, 79.5% of the reported cases were addressed. This effort highlighted the current lack of an official database that would provide firsthand knowledge of Antillean manatee stranding events in Colombia, thereby hindering timely and appropriate territorial management during response to the challenges faced by this species in the region. Furthermore, it underscores the need to implement a standardized response pathway for manatee cases, following appropriate protocols, and promoting the coordination of stakeholders within the regional stranding network in the middle Magdalena Basin. This approach, in addition to supporting the capacity building of communities, institutions, and organizations for improving response knowledge, conservation, and manatee recovery, is of paramount importance for the long-term sustainability of manatee populations in the region.

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

Mariana M. Moreira-Lima — 2024-04-28

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

Katherine Fiedler Choi Lima — 2024-04-28

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.

Manatees across borders: Introduction to the special issue on the biology and conservation of manatees

Ana Carolina Oliveira de Meirelles — 2024-04-28

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

Vera M F da Silva — 2024-04-28

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.

Where there’s smoke, there’s fire: Hypotheses for the high incidence of West Indian manatee calf strandings on the Brazilian semi-arid coast

Ana Carolina Oliveira de Meirelles — 2024-04-28

Antillean manatees feed on floating Halophila baillonii in Placencia Lagoon, Belize

Eric Angel Ramos — 2024-04-28