Trichechidae

Trichechidae is a family of large, fully aquatic, herbivorous mammals in the order Sirenia, commonly known as manatees, characterized by their streamlined bodies, paddle-like flippers, and rounded tails adapted for life in shallow coastal and riverine waters.^[1] The family comprises a single genus, Trichechus, with three extant species: the West Indian manatee (T. manatus), the Amazonian manatee (T. inunguis), and the West African manatee (T. senegalensis).^[1] Manatees belong to the order Sirenia, which evolved from terrestrial ancestors into fully aquatic forms during the Eocene epoch, approximately 50 million years ago. The family Trichechidae represents one of the most derived lineages within the paenungulate clade Afrotheria.^[2][3] Manatees can reach lengths of over 4 meters and weights exceeding 1,000 kilograms, featuring a rounded head with small eyes, a cleft upper lip for grasping vegetation, and dense bristles (vibrissae) that aid in detecting food.^[1] They inhabit warm, shallow waters across a wide range, including the coasts of the southeastern United States and the West Indies, the Amazon and Orinoco river basins in South America, and tropical West African rivers and coastal areas.^[1] As primary consumers of aquatic plants such as seagrasses and freshwater vegetation, manatees play a key ecological role in maintaining aquatic ecosystems, though they face significant threats from habitat loss, boat collisions, and historical hunting for meat and hides.^[1] Fossil records indicate that Trichechidae originated in the Early Miocene of South America, with the family representing one of only two surviving lineages in Sirenia alongside Dugongidae (dugongs).^[1] As of 2025, all three species are listed as vulnerable by the IUCN Red List due to anthropogenic pressures, underscoring the need for protected marine and riverine habitats to ensure their survival.^[1]

Taxonomy

Classification

Trichechidae is a family of mammals within the order Sirenia, classified hierarchically as follows: Kingdom Animalia, Subkingdom Bilateria, Infrakingdom Deuterostomia, Phylum Chordata, Subphylum Vertebrata, Infraphylum Gnathostomata, Superclass Tetrapoda, Class Mammalia, Subclass Theria, Infraclass Eutheria, Order Sirenia, and Family Trichechidae.^[4] The family was formally established by American ichthyologist Theodore Gill in 1872, as part of his systematic arrangement of mammalian families for the Smithsonian Institution's collection, where he defined Trichechidae under the superfamily Trichecoidea with the type genus Trichechus.^[5] All extant members of Trichechidae belong to the single genus Trichechus, originally described by Carl Linnaeus in 1758 in the tenth edition of Systema Naturae, initially placing manatees within the order Bruta alongside sloths and anteaters.^[6] No other genera are currently recognized within the family, distinguishing it from more diverse extinct sirenian lineages.^[1] Trichechidae is the sister family to Dugongidae within Sirenia, with the two differing notably in tail morphology: members of Trichechidae possess a horizontally flattened, rounded paddle-like tail fluke, in contrast to the notched, whale-like flukes of Dugongidae.^[7] This family-level recognition emerged in the 19th century, building on Linnaeus's genus-level description, as sirenian taxonomy evolved to separate manatees from dugongs based on anatomical distinctions formalized by Gill.^[5]

Phylogenetic relationships

Trichechidae represents one of the two extant families within the order Sirenia, alongside Dugongidae, with the divergence between these families estimated to have occurred at the Eocene-Oligocene boundary approximately 33.9 million years ago (95% highest posterior density: 36.7–31.7 Ma). This split marks the founding of crown-group Sirenia, with Trichechidae evolving primarily in freshwater and coastal environments of the Americas, while Dugongidae diversified in marine habitats globally before a Pliocene decline.^[8] Within the broader mammalian phylogeny, Trichechidae and Sirenia as a whole belong to the clade Paenungulata, which also includes the orders Proboscidea (elephants) and Hyracoidea (hyraxes), all sharing an afrotherian ancestry originating on Afro-Arabia during the Paleocene. Molecular and chromosomal studies consistently place Sirenia as sister to Proboscidea within Paenungulata, supported by shared syntenic associations such as human chromosome 5/21 and evidence of ancient chromosomal rearrangements conserved across these groups. The common ancestor of Paenungulata is estimated to have diverged from other afrotherians around 70–80 million years ago, with Sirenia's aquatic adaptations evolving from terrestrial paenungulate forebears.^[9][10] Molecular evidence from mitochondrial DNA, including complete mitogenomes and 12S rRNA sequences, robustly confirms the monophyly of Sirenia and its position within Afrotheria, with sirenians diverging from terrestrial ancestors shortly after the Cretaceous-Paleogene extinction event around 60 million years ago. These studies, utilizing cytochrome b and other mtDNA markers, reveal low genetic divergence among extant trichechids (e.g., Trichechus species splitting in the late Miocene to Pleistocene, ~6–1 Ma), underscoring a recent radiation influenced by geological events like the closure of the Tethys Sea. Key phylogenetic analyses, such as those revising early Oligocene sirenian systematics and incorporating fossil calibrations, further support these relationships by integrating morphological and genetic data to resolve stem- and crown-group dynamics.^[11][12][13]

Physical description

Morphology

Trichechidae, the family encompassing the three extant manatee species, exhibit a robust, streamlined body adapted for an aquatic lifestyle, typically measuring 2.8 to 4.0 meters in length and weighing 400 to 500 kilograms on average for adults, though maximum lengths reach up to 4.5 meters and weights up to 1,600 kilograms.^[14][15] The body is cylindrical and rounded, lacking a distinct neck due to fused cervical vertebrae, with paddle-like forelimbs and a flattened, horizontal tail fluke serving as the primary means of propulsion.^[14][15] No hind limbs are present, as the pelvic bones are fused and vestigial, reflecting their fully aquatic evolution.^[16] The skin of manatees is thick, tough, and wrinkled, providing protection against abrasions from their environment; it is nearly hairless but features scattered, sensitive bristles or vibrissae, particularly around the muzzle, and ranges in color from grayish to brownish.^[14][15] The head is rounded with a broad, square snout, small eyes positioned laterally, and no external ear pinnae, though internal ear structures are well-developed.^[15] A key feature is the prehensile upper lip, split in the middle and highly mobile, which aids in grasping vegetation; this lip is covered in vibrissae for tactile feedback.^[15][16] Dentition in Trichechidae is specialized for their herbivorous diet, lacking incisors or canines and instead featuring a series of continuously replacing molars known as "marching molars," where worn teeth at the front are shed and replaced by those emerging from the rear of the jaw throughout the animal's life.^[15] Typically, four sets of six to eight molars are present at any time, with the process ensuring functional grinding surfaces despite heavy abrasion from abrasive plant material.^[15] The forelimbs are modified into broad, flipper-like paddles with three to five nails on the leading edge (absent in the Amazonian manatee, Trichechus inunguis), used primarily for steering, slow maneuvering, and manipulating food.^[14][15] The tail is a rounded, horizontal paddle that moves up and down to generate thrust, enabling speeds of up to 8 kilometers per hour sustained and brief bursts to 24 kilometers per hour.^[14][16] While body size and some flipper nail counts vary slightly among species, these morphological traits are largely conserved across the family.^[14]

Sensory and physiological adaptations

Trichechidae, the family encompassing manatees, exhibit distinctive skeletal adaptations that support their fully aquatic lifestyle. Unlike most mammals, which possess seven cervical vertebrae, manatees have only six, a reduction that contributes to their shortened neck region.^[17] In adults, these cervical vertebrae often fuse, providing structural rigidity to the neck while limiting rotational mobility.^[18] This fusion contrasts with the highly flexible thoracic and lumbar regions of the spine, which enable powerful undulating movements essential for propulsion through water.^[19] The respiratory system of Trichechidae is adapted for obligate air-breathing in an aquatic environment. Manatees must surface regularly to breathe, typically every 3 to 5 minutes during active periods, though they can hold their breath for up to 20 minutes when resting.^[20] Their lungs are uniquely elongated, extending longitudinally along the dorsal side of the body cavity for over a meter in adults, which aids in buoyancy control and efficient gas exchange.^[21] Sensory adaptations in Trichechidae prioritize tactile and auditory cues over vision, suited to their murky, vegetated habitats. Eyes are small and positioned laterally, resulting in poor visual acuity and likely limited or absent color vision, with reliance on monocular cues for basic object detection.^[22] Hearing is acute, with sensitivity peaking between 6 and 20 kHz, allowing detection of environmental sounds for navigation in low-visibility conditions.^[23] Vibrissae, or specialized bristles, distributed on the lips and across the body surface, function as chemosensory and mechanosensory organs, enabling the detection of chemical cues from food sources and hydrodynamic disturbances in the water.^[24] Physiological traits of Trichechidae reflect their herbivorous, low-energy lifestyle in warm waters. They maintain a low metabolic rate, approximately 0.36 times that predicted for placental mammals of similar size, which conserves energy for prolonged submerged foraging.^[25] Thermoregulation depends on a combination of insulation from a subcutaneous fat layer—thinner than in many marine mammals—and behavioral strategies such as seeking warm shallow waters or clustering to retain heat.^[26] Digestion is slow and efficient, with high cellulose breakdown (up to 80%) in an enlarged hindgut, facilitating the processing of fibrous aquatic plants over extended retention times.^[27]

Diversity

Living species

The family Trichechidae comprises three extant species, all belonging to the genus Trichechus, which are fully aquatic herbivorous mammals classified as Vulnerable on the IUCN Red List (assessed 2015–2023) due to threats including habitat loss and hunting. Limited hybridization has been documented between T. manatus and T. inunguis in areas of sympatry, such as the Amazon estuary, despite their largely allopatric distributions.^[28][29] In 2025, a petition was filed with the U.S. Fish and Wildlife Service to reinstate the Florida manatee subspecies (T. m. latirostris) from threatened to endangered status under the Endangered Species Act.^[30] The West Indian manatee (Trichechus manatus) is the largest species, reaching lengths of up to 4.6 m and weights of up to 1,650 kg.^[31] It features three to four nails on each pectoral flipper, aiding in manipulation of food and social interactions.^[32] This species is divided into two subspecies: the Florida manatee (T. m. latirostris), found in the southeastern United States, and the Antillean manatee (T. m. manatus), distributed across the Caribbean and northern South America. The Amazonian manatee (Trichechus inunguis) is the smallest species, attaining maximum lengths of 2.8 m and weights of around 360 kg.^[33] Restricted to freshwater habitats in the Amazon Basin, it lacks nails on its pectoral flippers and typically displays a distinctive white or pinkish chest patch, along with thinner, more wrinkled skin compared to its congeners.^[33][34] The West African manatee (Trichechus senegalensis) grows to lengths of up to 4.5 m and weights of up to 750 kg, with a longer snout and greater mobility in riverine environments relative to other Trichechus species.^[35][36] It inhabits brackish and coastal waters along western Africa, possessing nails on its flippers similar to T. manatus, though it exhibits a smoother skin texture and more protruding eyes.^[35][37]

Fossil record

The fossil record of Trichechidae extends from the Late Oligocene to the present, with the subfamily Miosireninae appearing in the Late Oligocene to Early Miocene and Trichechinae from the Middle Miocene onward.^[38] The earliest known members, such as those in Miosireninae, date to approximately 28–23 million years ago and are primarily documented from European deposits along the Atlantic coast.^[38] This range reflects the family's origin in tropical and subtropical regions, with fossils becoming more abundant in the Miocene and Pleistocene.^[12] Several extinct genera highlight the family's prehistoric diversity. Miosiren, from the Oligocene to Early Miocene of Europe (e.g., Belgium and England), represents a primitive lineage within Miosireninae, characterized by simpler dental structures lacking the continuous tooth replacement seen in later forms.^[38] Potamosiren, known from the Early to Middle Miocene of northern South America (e.g., Colombia's Magdalena Basin), is one of the earliest trichechines and shows bilophodont molars adapted for herbivory.^[39] Other extinct taxa include Ribodon from the Miocene of the Rio Paraná region in South America and Trichechus hesperamazonicus from the Late Pleistocene (approximately 44,710 years before present) of southwestern Amazonia in Brazil.^[12] Additionally, the Pleistocene subspecies Trichechus manatus bakerorum, an extinct morphotype, is recorded from Gulf Coast sites in the United States.^[40] Key fossil sites underscore a historically broader distribution than today. In South America, Miocene formations such as those in Colombia's Honda Group and Peru's Pebas Formation yield early trichechids like Potamosiren, indicating an initial invasion of freshwater ecosystems.^[39] Pleistocene deposits along the Madeira River in Brazil preserve Trichechus hesperamazonicus, suggesting coexistence with ancestral Amazonian manatees.^[41] In North America, Pleistocene beach deposits in Florida and Texas document Trichechus manatus bakerorum, extending the family's range northward during warmer interglacial periods.^[40] Limited European fossils, primarily from Early Miocene sites in Belgium and England, imply a wider Paleogene-Neogene presence before regional extirpations.^[38] Evolutionary trends in the fossil record reveal adaptations from more primitive sirenian ancestors toward fully aquatic lifestyles, with Trichechidae exemplifying complete marine and freshwater specialization.^[12] Early forms like Miosiren retained basic dental patterns, while Miocene trichechines such as Potamosiren developed advanced features like supernumerary tooth replacement to handle abrasive aquatic vegetation, facilitating the shift to obligate herbivory in water.^[38] Over time, body sizes appear to have increased, as evidenced by the progression from smaller Miocene genera (e.g., Potamosiren) to larger Pleistocene and modern Trichechus species, supporting enhanced energy efficiency in tropical habitats.^[12] These changes align with geological shifts in the Amazon Basin, promoting diversification in riverine environments.^[12]

Distribution and habitat

Geographic distribution

The family Trichechidae, comprising three extant species of manatees, exhibits a disjunct distribution across tropical and subtropical regions of the Atlantic Ocean basin, with no evidence of trans-oceanic migration among populations.^[14][34] These species occupy coastal, estuarine, and riverine environments, but their ranges have contracted historically due to human activities such as overhunting and habitat alteration, particularly in pre-colonial and colonial eras when distributions were more continuous across certain regions.^[14][42] The West Indian manatee (Trichechus manatus) has the broadest range among the family, distributed patchily along the Atlantic and Gulf of Mexico coasts from the United States (including Florida and other Gulf Coast states) southward through Central America and the Caribbean to northeastern Brazil.^[14][43] This patchiness reflects the species' dependence on warm waters, resulting in fragmented populations separated by unsuitable cooler areas.^[14] Historically, the range extended more uniformly along the U.S. Atlantic and Gulf coasts, throughout the Caribbean, and to Brazil's Atlantic coastline, but local extirpations occurred in areas like Guadeloupe and parts of the Lesser Antilles due to intensive human exploitation.^[14] The Amazonian manatee (Trichechus inunguis) is the only exclusively freshwater species in the family and is confined to the Amazon River basin, spanning from Peru through Colombia, Ecuador, Guyana, Venezuela, and Brazil.^[34][44] Its distribution follows the Amazon River and its major tributaries, from the upper reaches to the estuary, but remains restricted within this basin without overlap with other manatee species.^[45] Historical records indicate a wider presence in pre-colonial times across the basin's waterways, with contractions attributed to human hunting pressures that reduced connectivity in some tributaries.^[34] The West African manatee (Trichechus senegalensis) inhabits coastal and inland waters along the West African shoreline, ranging from Mauritania in the north to Angola in the south.^[46][47] Populations extend up to 2,000 km inland along major river systems, including the Niger, Volta, and Senegal Rivers, forming a continuous but sparsely documented distribution across 20 countries.^[48][47] Prior to colonial-era human impacts, the range was likely more extensive and less fragmented, with overhunting leading to localized declines and range contractions in coastal and riverine areas.^[46]

Habitat requirements

Trichechidae species require warm water temperatures typically ranging from 20°C to 30°C to maintain thermoregulation, with prolonged exposure below 20°C leading to cold stress syndrome, hypothermia, and potential mortality.^[14][49] In regions with seasonal cooling, such as the Florida population of the West Indian manatee (Trichechus manatus), individuals migrate to warm-water refuges including natural freshwater springs or industrial effluents from power plants to survive winter temperatures.^[50] These aggregations can involve hundreds of individuals at sites like Blue Spring State Park, where stable temperatures around 22–24°C provide essential protection during cold snaps.^[49] Members of Trichechidae inhabit shallow coastal bays, estuaries, rivers, and associated wetlands, preferring depths of 1–3 meters where aquatic vegetation is abundant for foraging and resting.^[51][52] They generally avoid areas with fast currents exceeding 6 km/h, which hinder navigation and increase energy expenditure, opting instead for calm, protected waters that facilitate efficient movement and access to food resources.^[53] Habitat selection emphasizes proximity to submerged vegetation, such as seagrasses (Syringodium filiforme, Thalassia testudinum) in coastal zones for West Indian and West African manatees (T. senegalensis), or emergent and floating plants like water hyacinth (Eichhornia crassipes) and mangroves in riverine systems.^[14][54] Salinity tolerance varies across the family: the Amazonian manatee (T. inunguis) is strictly freshwater-dependent, inhabiting blackwater lakes, oxbows, and floodplain channels in the Amazon basin without tolerance for marine conditions.^[44] In contrast, West Indian and West African manatees are euryhaline, thriving in marine, brackish, and freshwater environments but periodically requiring access to lower-salinity waters for osmoregulation.^[2] Microhabitats include sheltered inlets and lagoons for calving and nursing, providing seclusion from predators and boat traffic, while warm refugia serve as seasonal aggregation points during adverse conditions.^[55]

Behavior and ecology

Diet and foraging

Trichechidae, the family encompassing manatees, are obligate herbivores that primarily consume aquatic vegetation, with documented diets including over 60 plant species across freshwater, estuarine, and marine habitats. In coastal regions, seagrasses such as Thalassia testudinum form a dietary staple, while freshwater environments feature plants like water hyacinth (Eichhornia crassipes) and emergent grasses including Echinochloa pyramidalis and Hymenachne amplexicaulis. Algae and mangrove leaves supplement the diet when accessible, particularly during high tides, though incidental ingestion of small invertebrates or fish occurs rarely and does not indicate carnivory.^{[32][56][57][58]} Adult manatees require substantial daily intake to sustain their metabolism, consuming 10-15% of their body weight in wet vegetation, equivalent to 40-60 kg for a typical 400-600 kg individual. They graze for 5-7 hours per day, using their prehensile upper lips—equipped with vibrissae for tactile detection—and foreflippers to grasp and uproot plants from the substrate. Foraging predominantly occurs in shallow waters less than 2 m deep, where manatees act as bottom-feeders, selectively cropping vegetation without disturbing roots extensively. Their molars, which continuously replace in a unique marching fashion, grind fibrous material, while hindgut fermentation in the capacious cecum and colon—comprising up to 70% of gut mass—facilitates microbial breakdown of cellulose, with digesta retention times of 146-147 hours.^[14][56][59] Foraging patterns exhibit flexibility, with manatees primarily diurnal but capable of nocturnal activity in certain contexts, such as Amazonian populations targeting riverside plants to avoid daytime disturbances. Seasonal shifts are pronounced in variable environments; during dry seasons, reliance increases on emergent and floating vegetation like Paspalum repens and Azolla caroliniana as submerged options diminish, maintaining dietary diversity without evidence of active predation or hunting behaviors.^[58][57][60]

Reproduction and development

Trichechidae exhibit a polygynous mating system, in which receptive females in estrus attract multiple males that form mating herds, often comprising 5 to 20 individuals, which can persist for days to weeks.^[61] These herds engage in competitive behaviors among males to gain access to the female, with no pair bonds formed.^[62] Mating occurs year-round without a fixed season, though peaks have been observed in winter for certain populations, such as those in Florida.^[63] Gestation in Trichechidae lasts approximately 12 to 13 months, after which females typically give birth to a single calf underwater, with twins occurring rarely.^[64] Newborn calves measure about 1 to 1.2 meters in length and weigh 27 to 32 kilograms, emerging tail-first or head-first to facilitate surfacing for their first breath.^[65][66] Births can occur at any time of year but show slight peaks in spring for some populations.^[67] Females provide extensive parental care, nursing calves with milk from mammary glands located behind the forelimbs for 12 to 18 months, during which the young remain dependent on the mother.^[68] Calves typically stay with their mothers for 2 to 3 years, gradually transitioning to independence by weaning onto a diet of aquatic vegetation while learning foraging behaviors.^[69] Sexual maturity is reached by females at 3 to 5 years of age and by males at 5 to 7 years, though variability exists across populations and individuals.^[70] In the wild, Trichechidae have a lifespan of 50 to 60 years, influenced by factors such as habitat quality and human impacts, with some individuals exceeding this in protected environments.^[71][72]

Social behavior and movement

Trichechidae, commonly known as manatees, exhibit a largely solitary social structure, with individuals typically traveling and foraging alone or in small, fluid groups of 2 to 5 animals that lack rigid hierarchies or territoriality.^[54] Larger temporary aggregations, sometimes exceeding 100 individuals, form at warm-water refuges during colder seasons to maintain body temperature, but these groups disband quickly and do not represent stable social units.^[73] The most enduring bonds occur between mothers and calves, which remain paired for up to 2 years, allowing the young to learn essential behaviors such as navigation and resource location through close association.^[54] Communication among manatees relies on acoustic and tactile signals, with vocalizations playing a key role in maintaining contact, particularly between mothers and calves. These include frequency-modulated chirps, squeaks, and squeals produced in the larynx, audible over distances up to 200 meters underwater and used to convey location, distress, or affiliation.^[74] Tactile interactions, such as gentle nudges or flipper touches, facilitate social recognition and bonding during brief encounters in groups.^[75] Manatees are slow-moving swimmers, cruising at average speeds of 5 to 8 km/h during routine activities, though they can achieve short bursts up to 24 km/h when evading threats or pursuing food.^[76] Daily travel distances typically range from 10 to 30 km, varying with habitat availability and season, while longer displacements occur during seasonal migrations to warmer waters; for instance, Florida manatees (Trichechus manatus latirostris) may cover hundreds of kilometers to reach industrial warm-water outflows in winter.^[77] These migrations follow learned routes, often along coastlines or rivers, and demonstrate spatial memory integrated with sensory cues like water temperature and salinity.^[54] Evidence of cognitive abilities in manatees includes associative learning, as calves acquire migration paths and foraging techniques by observing and following adults, contributing to their long-term survival in dynamic environments.^[54] Complex navigation relies on a combination of memory and heightened tactile senses from specialized facial bristles, enabling precise orientation over vast ranges without visual dependence.^[78]

Conservation

Population status

All three species within the family Trichechidae—the West Indian manatee (Trichechus manatus), Amazonian manatee (T. inunguis), and West African manatee (T. senegalensis)—are classified as Vulnerable on the IUCN Red List of Threatened Species based on 2023 assessments.^[75][33][35] The West Indian manatee has a range-wide population estimated at least 13,000 individuals as of a 2016 assessment by the U.S. Fish and Wildlife Service.^[14] Within this species, the Florida subspecies (T. m. latirostris) numbered approximately 9,790 in recent statewide estimates (circa 2023) by the Florida Fish and Wildlife Conservation Commission, with trends indicating stability or slight increases in protected areas.^[79][80] In contrast, the Antillean subspecies (T. m. manatus) shows declining abundance across much of its distribution, with a range-wide population of fewer than 7,000 individuals as of recent estimates; local estimates in regions like Puerto Rico ranged from 312 to 535 individuals based on 2010–2014 aerial data.^[43][14][81] The Amazonian manatee population is estimated at 8,000–30,000 adults based on assessments up to 2025, considered stable overall but fragmented into isolated subpopulations across Amazon basin waterways, limiting gene flow and resilience.^[82][83] Similarly, the West African manatee totals about 10,000 mature individuals as of recent assessments (circa 2025), yet exhibits a declining trajectory amid substantial data gaps that hinder comprehensive trend analysis.^[84][83][85] Monitoring efforts for Trichechidae populations employ aerial surveys for broad abundance counts, photo-identification to track individuals via unique scarring patterns, and genetic tagging for movement and kinship studies.^[86][87] These techniques have documented recovery in U.S. protected zones, where the Florida manatee population has grown significantly since the 1990s through enhanced habitat management and reduced mortality.^[14]

Threats

Trichechidae populations face significant habitat loss primarily from coastal development, dredging activities, and agricultural expansion, which degrade essential seagrass beds and aquatic vegetation critical for foraging. In Florida, dredging and shoreline construction have reduced seagrass coverage by altering water quality and increasing sedimentation, while agricultural runoff introduces excess nutrients that promote algal overgrowth and further diminish suitable habitats. In riverine systems of the Amazon and West Africa, water extraction for irrigation and hydropower dams lowers water levels, fragmenting habitats and exposing manatees to additional risks during dry seasons.^[49][88][89] Direct mortality from human activities is a leading cause of death for Trichechidae, with boat collisions being particularly severe for the Florida manatee subspecies, accounting for approximately 20% of annual mortalities through propeller strikes and blunt trauma. Entanglement in fishing gear, such as nets and lines, also results in injuries or drowning, with fishery-related debris implicated in over 70% of documented marine debris fatalities in Florida manatees from 1993 to 2012. Hunting persists as a threat in parts of Africa and the Amazon, where West African and Amazonian manatees are targeted for bushmeat, despite legal protections, contributing to localized population declines.^[90][91][89] Environmental factors exacerbate vulnerabilities, including cold stress events that induce hypothermia in manatees unable to maintain body temperature below 20°C (68°F), leading to metabolic disorders and increased mortality during winter cold snaps in subtropical regions. Harmful algal blooms, such as red tides caused by Karenia brevis, release brevetoxins that cause neurotoxic effects like seizures and respiratory failure upon ingestion through contaminated seagrass, resulting in mass die-offs along Florida coasts. Pollution from heavy metals, including mercury, lead, and cadmium, bioaccumulates in manatee tissues via their herbivorous diet, potentially impairing immune function and reproduction, as evidenced by elevated concentrations in Florida and Antillean manatees.^[92][93][94] Climate change poses emerging risks by warming coastal waters, which may shift foraging ranges and disrupt seasonal migrations, while sea-level rise inundates shallow seagrass habitats and increases salinity in freshwater systems frequented by Amazonian and West African manatees. Intensified storm frequency from hurricanes and cyclones further damages seagrass beds through scouring and sedimentation, compounding habitat degradation and exposing manatees to injury during extreme weather. These changes contribute to broader population stresses observed in recent years.^[95][96]

Conservation efforts

Conservation efforts for Trichechidae species, encompassing the three manatee species of the genus Trichechus, involve a combination of legal frameworks, organizational initiatives, habitat management strategies, and ongoing research to mitigate threats and promote recovery.^[14] Legal protections form the foundation of these efforts. In the United States, the Florida manatee (Trichechus manatus latirostris), a subspecies of the West Indian manatee, has been listed as threatened under the Endangered Species Act since 2017, providing safeguards against take and habitat destruction. In January 2025, following a five-year status review, the U.S. Fish and Wildlife Service proposed to retain threatened status for the Florida manatee and uplist the Antillean manatee to endangered.^[14][30] All species within Trichechidae—Trichechus manatus, Trichechus inunguis, and Trichechus senegalensis—are included in Appendix I of the Convention on International Trade in Endangered Species (CITES), prohibiting international commercial trade to prevent overexploitation.^[97] Additionally, marine protected areas in the Caribbean, such as those in Puerto Rico and Panama, designate critical habitats like seagrass beds and estuaries to restrict human activities and support Antillean manatee (Trichechus manatus manatus) populations.^[98] Key initiatives are led by dedicated organizations and partnerships. The Save the Manatee Club, founded in 1981, advocates for manatee protection through public education, policy advocacy, and habitat restoration projects, including collaborations with government agencies.^[99] The IUCN Species Survival Commission's Sirenia Specialist Group coordinates global research, provides conservation recommendations, and assesses species status for the IUCN Red List to guide international efforts.^[100] Rehabilitation centers play a vital role in rescue operations; for instance, the Cincinnati Zoo serves as a second-stage facility in the U.S. Fish and Wildlife Service's Manatee Rescue and Rehabilitation Partnership, where orphaned or injured manatees receive care before release back into the wild.^[101] Habitat management focuses on reducing human-induced pressures. In Florida, the Florida Fish and Wildlife Conservation Commission enforces boat speed zones in manatee aggregation areas, limiting vessel speeds to idle or slow to prevent collisions, with zones active seasonally from November to March.^[102] Seagrass restoration initiatives, such as those in the Indian River Lagoon, involve transplanting beds and improving water quality to rebuild foraging habitats essential for West Indian manatees.^[49] In the Amazon Basin, organizations like the Institute for Ecological Research (IPÊ) implement anti-poaching patrols and community education to curb illegal hunting of Amazonian manatees for bushmeat.^[103] Similarly, in West Africa, the African Aquatic Conservation Fund conducts enforcement and awareness campaigns to combat poaching of West African manatees in coastal and riverine systems.^[104] Research and monitoring efforts employ advanced techniques to inform conservation actions. Satellite tagging by the Florida Fish and Wildlife Conservation Commission tracks individual manatee movements in real-time, revealing migration patterns and habitat use to refine protected areas.^[105] Population modeling, developed by the U.S. Geological Survey and partners, integrates demographic data to project trends and evaluate recovery scenarios for Florida manatees.^[106] International agreements like the Convention on Migratory Species (CMS) facilitate cooperation for transboundary populations, with the West Indian manatee (T. manatus) listed in Appendix II to promote conservation of migratory routes in shared waters.^[107][108]