Manatee Conservation Research Articles

Plastic pollution on beaches in an Antillean manatee conservation area, Brazil

The presence of plastic debris along shorelines is a widespread problem, and plastic debris can interact directly with marine wildlife. In northeast Brazil, the Antillean manatees are the most common marine mammals and use estuarine waters mainly as their home range. We aimed to investigate the characteristics of plastic debris on the estuarine-oceanic continuum and the accumulation density of plastic on beaches. The density of plastic debris on beaches located in transitional areas was 7–10-fold greater than that on beaches in estuarine and oceanic areas. Fragments were considered the most abundant form of plastic debris on all the beaches. Our findings could lead to improved pollution management in this marine protected area, principally due to the risks of remobilizing small plastic particles through tides and wind effects that scatter them in resting and feeding manatees areas.

Not Everyone Likes Manatees: Fishers' Perceptions Unveil Opportunities and Challenges for Manatee Conservation in the Swamp Complex of Ayapel, Colombia

ABSTRACTGreater Caribbean manatees Trichechus manatus manatus face complex conservation challenges throughout their distribution range, many of which are associated with human factors; and in consequence, the subspecies is considered Endangered (EN) by the International Union for Conservation of Nature (IUCN). Human‐related threats as hunting for meat consumption, collisions with boats, entanglement in fishing nets, pollution and loss of habitat put the Greater Caribbean manatee at risk in Colombia. Studies aiming to describe traditional knowledge and local perceptions provide information that can be useful to design local manatee conservation programmes. We analyse the fishers' perceptions regarding manatees in Ayapel, Córdoba. One hundred semi‐structured interviews were conducted, focusing on personal data, fishing practices, perceptions and knowledge about the manatees. According to the interviews, bycatch is the greatest threat to manatees (56%), followed by pollution (16%), whereas boat collisions (12%), hunting (11%) and drought (5%) are lower ranking threats. Our results demonstrated that participants have a good understanding of manatee biology and ecology. However, a human–manatee conflict was evidenced, as 39% of fishers consider that manatees negatively impact fishing by competition for the fishing resources and/or by damaging fishing gear. We recommend strengthening awareness about the importance of manatee to guarantee an optimal management of this subspecies and its habitat. Fishers should be directly involved in the formulation of management and conservation plans for the subspecies, as their knowledge becomes critical to understanding and mitigating the risks to manatee populations. This work has a clear application to understand the human factor in manatee recovery not only in our study area but also in other locations where manatees share habitat with people, particularly in marginalized human communities.

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

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

Density and abundance estimate of Antillean manatees (Trichechus manatus) within a landlocked lake in Southeastern México

Manatees are threatened along their range. In México, this species is listed as endangered. Manatee conservation strategies require density or occupancy estimates, especially in areas where species face survival risks. On turbid waters, like those found in rivers and lakes of the Southern Gulf of México coast, visual methods used to detect and count manatees underestimate actual numbers. Our goal was to estimate the density and abundance (N) of Antillean manatees in a small State Natural Protected Area, where a manatee population of unknown size inhabits. We performed line transects using a side scan sonar to detect animals and mark-recapture in the isolated population of manatees within Laguna de las Ilusiones, México, a landlocked lake that excludes transit. Using distance sampling from 14 boat trips, estimates of density and abundance were 15.5 manatees km-2 and 27 ± 5 manatees in the lake (CV ≈ 16.6 %). With MARK, from six capture events and 19 individual encounter records, the abundance estimated was 24 manatees (CV ≈ 16 to 24 %). Previous number of manatees were based only on visual surveys, which reported at least seven manatees. Density is lower than other similar studies along narrow waterways in important areas in México and other Central and South America countries. Studying this endangered subspecies is limited by cryptic habits, turbid waters, poor funding, and low densities, making density or abundance estimates difficult. However, within particular areas and established monitoring areas, these methods could be useful to generate baselines for conservation strategies.

Behaviour and occurrence of the Antillean manatee (Trichechus manatus manatus) in relation to habitat characteristics and the influence of human activities in a protected area in north‐eastern Brazil

Abstract While all sirenian species are considered sentinel animals for the ecological health of their habitat, they are currently facing extinction risk. The Antillean manatee (Trichechus manatus manatus) is classified as an endangered species in Brazil. Its distribution and behaviour are mainly influenced by the presence of aquatic vegetation, freshwater and anthropogenic activities, as well as by variations in tides, temperature and salinity. The study investigated the behaviour of manatees in the Barra do Rio Mamanguape Environmental Protection Area in north‐eastern Brazil, and the relationship between these behaviours and the biotic and abiotic characteristics of this estuarine environment. The behavioural data were collected between November 2016 and May 2017, during 35 days of monitoring. The records of surface behaviour were obtained using animal focal sampling. Anthropogenic activities were recorded qualitatively and quantitatively during the surveys. Warmer water (30–31°C), reduced turbidity (1–2 m) and sandy sediments had a significant influence on the behaviour of the manatees. The manatees presented neutral behaviour more often than expected in response to anthropogenic activities, which indicates that the animals were undisturbed by these activities. This is the first systematic study of the influence of biotic and abiotic factors on the behaviour and ecology of Antillean manatees in a protected area of a tropical region, providing important new insights into the behavioural ecology of an endangered species. The Barra do Rio Mamanguape Environmental Protection Area seems to fulfil the goal of adequate management and conservation of manatees in a tropical region. Specifically, it shows that appropriate management, law enforcement and inspection measures are essential for maintaining endangered populations.

Observations on the feeding activities of the West African Manatee, Trichechus senegalensis Link, 1795 in a semi-wild environment

The presence of the West African manatee, Trichechus senegalensis in a semi-wild holding facility in Little Stream Farm, Ibesikpo Asutan Local Government Area, presented an opportunity to study directly, aspects of their biology, which hitherto were little known. This study was conducted to identify their plant food preferences and feeding behaviour as a reflection of what may approximate their activities in the wild. The selected plants were weighed (wet weight in kg) with spring balance in batches of 3kg per plant species and offered in batches to the manatee for a specified period (initially for 24 hours, then 4 hours and 10 hours). Of the 15 plant species presented, Emilia sonchifolia, Commelina diffusa, Nymphaea sp., Panicum laxum, Eleusine indica and Rhynchosia sp. had high preference levels while the quantity of Chromolaena sp. consumption was minimal. Bambusa sp., Heliotropium indicum, Ludwigia abyssinica and Hyptis lanceolata were ignored by the animal on repeated presentations. Studies on day-time and night-time feeding showed little difference in quantities of food consumed. However, the maximum consumption of 7kg was observed at daytime feeding on day 4 of the 14 days trial. The result showed that in the event of West African manatee rescue and fostering in temporary holding facilities, these plants’ checklists may come in handy as food materials. They may also come for important considerations as plants whose natural growth and propagation should be encouraged in areas designated for West African manatee conservation.

Manatee cognition in the wild: an exploration of the manatee mind and behavior through neuroanatomy, psychophysics, and field observations.

Cognition refers to the mechanisms for acquiring, processing, storing, and acting on information, all of which are critical to understanding the behavior of animals. These mechanisms are poorly known in manatees, especially how they are expressed in the wild. To expand our understanding of manatee cognition, we gathered information from behavioral experimentation in the laboratory, neuroanatomical research, controlled field studies, integrated laboratory and field measurement, and natural history observations (published reports, written surveys, and interviews with knowledgeable observers). Laboratory research, both neuroanatomical and behavioral, provided the most empirical data, primarily on sensory/perceptual capacities. Inferences from these data and narratives from surveys and interviews illuminated possibilities for higher order cognition. Evidence from field measurements was sparse, although substantial amounts of information have been collected from tracking data and to a lesser extent vessel impact studies, which can be used to infer cognitive attributes. Manatees are tactile-auditory specialists with complementary visual and chemosensory abilities. They demonstrate learning characteristics typical of vertebrates. Movement tracking data plus direct observations suggest that they have good spatial cognition, indicated by their ability to traverse complicated water networks and memory for foraging and warm water sites. They engage in a wide range of play-like, object manipulation, and mimetic behaviors, which suggests cognitive capacities beyond basic associative learning. Understanding manatee cognition beyond the laboratory will be necessary for conservation of manatees as they face challenges such as habitat degradation and threats from water-borne vessel traffic. There is a clear need for more direct research in natural settings.

The existence value of the Antillean manatee in the unprotected Hondo River (Mexico) as a fundamental component for its conservation

The Hondo River is the natural border between Mexico and Belize, and it is part of the distribution area of the Endangered Antillean manatee Trichechus manatus manatus. Currently, the Hondo River does not have any special protection. Employing qualitative research methods, we documented the social perception and local knowledge from riverside communities to assess conservation status and trends of manatees in the area. Fifty semi-structured interviews were carried out to river users in 16 Mexican communities, distributed in six segments along the riverbed. The claims of the inhabitants agree with boat-based surveys: most of the current and historical manatee sightings were reported in segments of the main watercourses, but also in small tributaries, which are usually shallow and rich in aquatic vegetation. Additionally, the local perception about manatee conservation status can be helpful to understand population trends and threats: 48 % of the interviewees claimed that nowadays the number of sighted manatees is less than that observed 10 years ago. The responders identified water pollution due to cane cultivation practices, motorized vessels traffic, and presence of fishing nets as potential threats to manatees. This study provides evidence of relevant local knowledge about the manatee ecology and its habitat, critical in the construction of binational conservation strategies for the species. Therefore, local resources users may play an increasingly significant role in manatee management and monitoring.Although manatees are poached for their meat in several areas of their distribution, the most common value attributed to manatees in Hondo River was non-use existence values. Local people recognize the challenges to observe this cryptic species in this river, but also identified manatees as potential flag species, suggesting that it may represent a valuable resource for ecotourism. We suggest that the non-extractive use of manatees has the potential for promoting species conservation and local economic growth.

Reproductive success of Antillean manatees released in Brazil: implications for conservation

AbstractActions to rescue, rehabilitate and release calves of manatees are the main initiatives and strategies for conservation of the species in Brazil. The survival rate of animals in a natural environment and the reproductive success, identified by birth records, are some of the indicators used to estimate the release success for manatees. This study evaluated the effectiveness of releases of West Indian manatees based on the reproductive success of rescued animals that were released back into the wild in Brazil. Twenty-two female manatees were released in the states of Alagoas (into an extinct area) and Paraíba (into an existent population) from 1994–2020. Six females gave birth to 13 calves, all in Alagoas State. The average age of the first calving event was 11.7 (±1.49) years and 8.0 (±1.41) years after release. Among the females that had more than one calving, the average was 3.6 (±1.18) years between each calving. All calves observed were born alive; nevertheless, three (23.1%) died a few weeks after birth. In general, females rehabilitated in captivity and released in the wild were able to reproduce, especially in protected areas. This study emphasizes the need to intensify actions for the conservation of manatees and their habitats in order to achieve healthier wild populations.

Home ranges of released West Indian manatees Trichechus manatus in Brazil

AbstractThe distribution of the Vulnerable West Indian manatee Trichechus manatus is influenced by physical and environmental factors such as water salinity, temperature and depth, freshwater supply and the availability of food resources. In Brazil, information on the habitat use of this species is insufficient for effective conservation. Here, we monitored manatees that had been found stranded as calves, rehabilitated in captivity and subsequently released, to identify their home ranges and examine their adaptation to life in the wild. The study, which involved monitoring six manatees using satellite and VHF telemetry systems, was conducted during 2016–2019 in the states of Paraíba, Sergipe and Bahia in north-eastern Brazil. Home range size of individuals was 2.56–42.07 km2 and all fidelity sites (areas used most frequently) were within protected areas. The longest distance travelled from the coastline upriver was 14.24 km and the longest distance offshore was 0.93 km. There were no significant differences in home range data between the dry and rainy seasons, but there was significant difference between the sexes, with males travelling across larger areas than females. All but one of the six individuals met the majority of indicators established in the Brazilian Manatee Reintroduction Protocol, and thus were considered to have successfully adapted to the wild. Our study provides information on patterns of habitat use and areas intensely used by manatees, which can assist protected area managers in defining priority areas for manatee conservation in Brazil.

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.

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.

Management effectiveness in marine protected areas for conservation of Antillean manatees on the eastern coast of the Yucatan Peninsula, Mexico

Abstract This study evaluated management effectiveness in three marine protected areas (MPAs) for conservation of the Antillean manatee (Trichechus manatus manatus Linnaeus 1758), located on the eastern coast of the Yucatan Peninsula, Mexico. The MPAs evaluated were the Yum‐Balam Flora and Fauna Reserve, Sian Ka'an Biosphere Reserve, and Chetumal Bay Manatee Sanctuary. The extent of the traditional, popular, and scientific manatee knowledge and research were assessed, as well as the prescribed conservation management actions, relevant stakeholders, and the degree of inclusion of manatee species in the management schemes of these MPAs. Four general criteria, 12 specific criteria, and 62 indicators were developed. In total, 199 interviews were completed in seven communities of the MPAs in order to determine the perception of the social, economic, and conservation impacts of the manatee and its management. Although the evaluated MPAs were not wholly comparable among themselves due to their different management categories and schemes, administration, socio‐economic context, and the dynamics and conflicts encountered, a comparison was conducted using standardized criteria and a categorical scale in order to evaluate the level of effectiveness of each MPA. The MPA with the highest management effectiveness in manatee conservation was found to be the Chetumal Bay, with an effectiveness classed as good (71%), followed by Sian Ka'an with intermediate effectiveness (53%) and Yum‐Balam, also with intermediate effectiveness (43%). The relationships between the key stakeholders of the three MPAs and economic activities such as fishing and tourism are the factors that most influence the effectiveness of management for manatee conservation.

History and conservation status of the Antillean manatee Trichechus manatus manatus in Hispaniola

AbstractTo summarize the state of knowledge of the Endangered Antillean manatee Trichechus manatus manatus in Hispaniola, which comprises the Dominican Republic and Haiti, I reviewed documentary archives from pre-Columbian times to 2013. Manatees were historically abundant in Hispaniola but were hunted for centuries for their meat and other body parts for diverse uses. By the end of the 19th century manatees had become relatively rare around the island. Nevertheless, manatees remain widespread along the coast and occasionally occupy freshwater habitats in the Dominican Republic. In Haiti recent manatee sightings were restricted to two coastal areas. Currently, the manatee population of Hispaniola is perceived to be declining. The most commonly reported threats to the species include hunting, entanglement in fishing gear, boat strikes and disturbance by boat traffic, pollution, and habitat degradation and destruction. In the Dominican Republic longstanding national laws and international agreements protect the species and its habitat, and past conservation actions have raised public awareness about the status of the manatee. In Haiti knowledge of manatees is extremely limited and the species is not legally protected. I propose country-specific and binational recommendations to improve the contemporary conservation of manatees in the Dominican Republic and Haiti.

Occurrence patterns of African manatees, conflicts with humans, and local perception in the Southern Korup Area, Cameroon

Abstract The African manatee has been poorly studied throughout its range and is heavily hunted. This study aimed at discerning patterns in manatee sightings and emerging conflicts with humans, as well as the local perception of manatees, outside the southern periphery of Korup National Park, Cameroon. The study investigated whether patterns in manatee sightings and manatee‐related conflicts differ between aquatic systems in southern Korup, and which demographic variables determine perceptions of the manatee in the study area. For this purpose, the study used a three‐stage stratified random sampling design with a structured questionnaire to survey 101 local fishers. The reported patterns of manatee sightings and manatee‐related conflicts were as follows: in the Nyangorobe River during the wet season only, where crop raiding and net destruction by manatees were reported; in the Ndian River and the mangrove estuary only during the dry season, where fish theft and net damage were reported; and in the Moko River during both seasons, where crop raiding, fish theft, and net destruction were reported. Reducing these conflicts is likely to increase local support for the conservation of manatees, because fishermen kill them in response to net destruction and fish loss. Most reported sightings were at waterway intersections and river bends, suggesting that waterway connectivity is important to manatees for dispersal, foraging, and escape from danger. The log‐odds probability of negative perception decreased significantly with awareness of manatee protected status but increased with age and primary or higher education level. These findings have implications for community outreach focused on raising awareness of the importance of manatee conservation by schoolchildren and the public.

Population estimates of Antillean manatees in Puerto Rico: an analytical framework for aerial surveys using multi-pass removal sampling

AbstractEffective management of the threatened Antillean manatee (Trichechus manatus manatus) in Puerto Rico requires reliable estimates of population size. Estimates are needed to assess population responses to management actions, and whether recovery objectives have been met. Aerial surveys have been conducted since 1976, but none adjusted for imperfect detection. We summarize surveys since 1976, report on current distribution, and provide population estimates after accounting for apparent detection probability for surveys between June 2010 and March 2014. Estimates in areas of high concentration (hotspots) averaged 317 ± 101, three times higher than unadjusted counts (104 ± 0.56). Adjusted estimates in three areas outside hotspots also differed markedly from counts (75 ± 9.89 versus 19.5 ± 3.5). Average minimum island-wide estimate was 386 ± 89, similar to the maximum estimate of 360 suggested in 2005, but fewer than the 700 recently suggested by the Puerto Rico Manatee Conservation Center. Manatees were more widespread than previously understood. Improving estimates, locally or island-wide, will require stratifying the island differently and greater knowledge about factors affecting detection probability. Sharing our protocol with partners in nearby islands (e.g., Cuba, Jamaica, Hispaniola), whose populations share genetic make-up, would contribute to enhanced regional conservation through better population estimates and tracking range expansion.El manejo efectivo del manatí antillano amenazado en Puerto Rico requiere estimados de tamaños de poblaciónes confiables. Dichas estimaciones poblacionales son necesarias para evaluar las respuestas a las acciones de manejo, y para determinar si los objetivos de recuperación han sido alcanzados. Se han realizado censos aéreos desde 1976, pero ninguno de ellos han sido ajustados para detecciones imperfectas. Aquí resumimos los censos desde 1976, actualizamos la distribución, y reportamos los primeros estimados poblacionales ajustados para la probabilidad de detección aparente en los censos de Junio 2010 a Marzo 2014. Las estimaciones poblacionales en áreas de mayor concentración del manatí promedió 317 ± 103, tres veces más abundante que los conteos sin ajuste (104 ± 0.56). Las estimaciones poblacionales en tres áreas fuera de las áreas de mayor concentración del manatí también fueron marcadamente diferentes (75 ± 9.89 vs 19.5 ± 3.5). El estimado mínimo poblacional en la isla entera fue de 386 ± 89, similar al estimado máximo de 360 sugerido en el año 2005, pero menor a los 700 sugeridos recientemente por el Centro de Conservación de Manatíes de Puerto Rico. Documentamos que el manatí tiene una distribución más amplia de lo que se sabía con anterioridad. El mejoramiento de los estimados poblacionales locales o a nivel de isla requerirá que se estratifique a la isla en forma diferente y que se investiguen los factores que influencian a la probabilidad de detección. Compartir protocolos como este con colaboradores de islas vecinas (por. ej., Cuba, Jamaica, Española), cuyas poblaciones de manatíes comparten material genético, contribuiría a la conservación regional mediante mejores estimaciones poblacionales y monitoreo de la expansión de su ámbito doméstico.

Riverine people's knowledge of the Vulnerable Amazonian manatee Trichechus inunguis in contrasting protected areas

AbstractTraditional knowledge gained through daily interactions with the environment can yield insights into processes at temporal or spatial scales that may be overlooked by conventional scientific research. Ninety interviews were conducted with riverine people in the vicinity of Anavilhanas National Park, Tapajós–Arapiuns Extractive Reserve and Tapajós National Forest in the Brazilian Amazon, with the aim to increase knowledge of the feeding habits of the Amazonian manatee Trichechus inunguis and evaluate its conservation status in contrasting protected areas. In Anavilhanas respondents identified 31 plant species consumed by the manatee, of which vines had the highest cognitive salience index value (the summed importance of each plant species), even though they are available to manatees only during the high-water season. In the Tapajós region 37 plant species were identified, with submerged species with floating leaves being the main component of the manatee's diet. Although hunting has declined it still occurs in Anavilhanas, which is susceptible to environmental crimes because of its proximity to urban centres. Manatee hunting seems to be infrequent in the Tapajós region, having little impact on the population. Given the broad knowledge within the local community about the Amazonian manatee, involvement of riverine people in manatee conservation activities is fundamental for reducing threats and increasing conservation effectiveness.

Is captive breeding a priority for manatee conservation in Mexico?

AbstractThe Endangered Antillean manateeTrichechus manatus manatusis one of the most threatened aquatic mammal species in Mexico and the wider Caribbean region. The decline of this subspecies is mainly a result of historical exploitation and the impact of current coastal development. The conservation strategies adopted for the Antillean manatee include habitat protection, reduction of the most severe threats, and the rescue of stranded, orphaned or injured individuals and their management in captivity. This latter strategy has produced positive outcomes in some countries but has been the subject of controversy in others, including Mexico. We analyse the benefits and challenges associated with the management of captive manatees in Mexico, and the consequences of a lack of government policy and strategy for the post-rehabilitation release of individuals. We describe the evolution of this controversy from 1997–2017 in Mexico, analyse the consequences and implications for the conservation of the species, and propose an integrated management strategy that could address the issues raised. Although this strategy has been developed in the context of Mexico, it is applicable to management of this species across the Caribbean region.

Status and conservation of manatees in Cuba: historical observations and recent insights

The Antillean manatee (Trichechus manatus manatus Linnaeus, 1758) is classified as endangered by the International Union for Conservation of Nature because of reduced numbers and habitat loss. Existing information about this species in Cuba is limited, but it can be synthesized into useful guidance for strategies to protect and rehabilitate this population. Anthropogenic threats have been reported to have had detrimental effects on manatees since 1970, with a major factor being illegal hunting. Information obtained through interviews of fishers, and boat and aerial surveys has identified the Ensenada de la Broa and Hatiguanico River on the Zapata Peninsula as important areas for manatees. Historically, manatees frequented rivers and other freshwater habitats, but currently they are encountered primarily in estuarine and coastal waters, which makes availability of fresh water an important consideration. There is a pressing need to gather additional and more reliable data on the abundance, distribution, and health of Antillean manatees in Cuba as a basis for more effective and efficient initiatives to protect and rehabilitate this population.

Relative abundance of Antillean manatees in the Pantanos de Centla Biosphere Reserve in the coastal plain of Tabasco, Mexico

Abundance estimates for the Antillean manatee, Trichechus manatus manatus, in the southern Gulf of Mexico are based on interviews, mortality reports, and opportunistic sightings. The lack of quantitative data is explained by the complexity of hard-to-access fluviallake systems, low water transparency, and the elusive behavior of manatees. Side-scan sonar is a promissory tool to detect and count manatees in fluvial systems. The Pantanos de Centla Biosphere Reserve (PCBR), in the coastal plain of Tabasco (Mexico), could play a key role in the regional conservation of manatees, but it is under constant pressure, especially from the oil and gas industry, and it is important to generate quantitative data for this area. The objective of this study was to quantify the relative abundance of manatees at 4 selected sites within PCBR and at 2 reference sites outside the reserve using side-scan sonar, as a basis for the long-term monitoring of the species and to determine the importance of the reserve for regional manatee conservation. We conducted 5 to 7 boat surveys on 10-km line transects along selected water courses and recorded 63 manatee sightings. Manatees occurred at all sampling sites and abundance increased upriver. The site with the highest mean abundance (5.17 ± 1.9 manatees/10 km) was located at the southeastern end of PCBR. There was statistical difference among sites. The southeastern portion of Tabasco is a key region for manatee conservation and management in Mexico. PCBR is a key regional feature but it is necessary to define protection strategies within and beyond its southern limits.