Dugong

The dugong (Dugong dugon) is a fully aquatic marine mammal and one of four extant species within the order Sirenia, a group comprising modern sea cows. It is the only surviving representative of the family Dugongidae, following the extinction of Steller’s sea cow in the eighteenth century. Found throughout the Indo–West Pacific, the dugong inhabits coastal waters in around forty countries, with its most stable populations occurring along the northern coast of Australia. Its distribution closely follows the presence of seagrass meadows, on which it is almost entirely dependent for food.
Known historically for its importance in coastal cultures and hunted for its meat and oil, the dugong has undergone significant population declines. Fragmented distribution, habitat loss and human impacts have contributed to its classification as Vulnerable by the International Union for Conservation of Nature (IUCN). With a life expectancy exceeding seventy years yet a slow reproductive rate, the species is particularly susceptible to decline.

Evolutionary Background

The evolutionary history of dugongs is intertwined with that of all sirenians, the only marine mammals that are exclusively herbivorous. Sirenians have a fossil record dating to the early Eocene, approximately fifty million years ago. They reached moderate diversity during the Oligocene and Miocene but later experienced reductions attributed to climatic cooling, shifts in oceanographic conditions and anthropogenic pressures.
Taxonomically, the term dugong is rooted in Visayan languages of the Philippines, becoming widely adopted in European scholarship through the writings of Buffon in the eighteenth century. Dugong dugon was originally classified in the manatee genus Trichechus before being reassigned to its own genus and ultimately its own family. Molecular and anatomical evidence places sirenians closer to elephants and hyraxes than to other marine mammals. Fossils indicate that ancestral dugongs likely inhabited the ancient Tethys Ocean, with the divergence of dugongid and manatee lineages occurring in the mid-Eocene. Recent genetic studies reveal distinct maternal lineages within Australia and a separate Southeast Asian population, although the boundaries between these groups remain imprecisely defined.

Distribution and Habitat Characteristics

Dugongs occupy shallow, warm coastal zones that support extensive seagrass systems. These environments include sheltered bays, mangrove channels, lagoons, and waters surrounding large inshore islands. Inter-reefal areas on continental shelves also sustain suitable foraging grounds. The species’ stronghold lies between Shark Bay and Moreton Bay in Australia, where habitat availability and favourable environmental conditions align.
Because dugongs are strict herbivores relying primarily on seagrass, their movement patterns, distribution and population densities directly reflect seagrass health. This dependence makes them vulnerable to habitat disturbances such as sedimentation, coastal development, destructive fishing practices and extreme weather events.

Anatomy and Morphological Adaptations

The dugong has a large, streamlined fusiform body adapted for aquatic life. Its smooth skin, pale at birth and darkening to shades of brown or grey, often hosts algae that modify external colouring. Sparse sensory hairs cover the body, with a concentration around the snout, enhancing tactile perception during foraging.
Several key features distinguish the dugong from the manatee, notably its fluked, dolphin-like tail and sharply downturned snout. These adaptations aid in bottom-feeding, allowing the animal to uproot seagrass efficiently. The upper lip is muscular and horseshoe-shaped, functioning much like a prehensile tool to grasp vegetation. The forelimbs are paddle-like flippers lacking nails, assisting with steering, stabilisation and manoeuvring.
Other notable characteristics include:

• Skeletal specialisation: Dugongs exhibit pachyostosis—dense long bones with minimal marrow—which helps maintain neutral buoyancy just below the water surface.
• Dentition: They have simple, peg-like molars that do not undergo continuous horizontal replacement, unlike those of manatees. Males develop small tusks at puberty, while females’ tusks usually remain unerupted until later in life.
• Physiology: Long lungs and elongated kidneys support life in saline environments. Their blood clots quickly, and their ears, lacking external pinnae, are adapted for underwater sound detection despite the species’ limited vision.

The vertebral column consists of between fifty-seven and sixty vertebrae, and the brain accounts for approximately 0.1 per cent of total body weight—typical for a specialised herbivorous marine mammal.

Behaviour and Ecological Role

Dugongs are primarily solitary or found in small groups, although larger aggregations occur where seagrass resources are abundant. They spend much of their time grazing on seagrass species, often leaving distinctive feeding trails on the seabed. Their slow metabolism and low-energy diet shape a relatively sedentary lifestyle characterised by gentle movement and periodic surfacing for air.
As major consumers of seagrass, dugongs play a vital ecological role in maintaining the productivity and health of seagrass meadows. Their grazing encourages nutrient cycling, prevents overgrowth and promotes seagrass regeneration. These ecosystems, in turn, support numerous fish, invertebrates and marine organisms, making dugongs important contributors to coastal biodiversity.

Threats and Conservation Challenges

Dugong populations have declined significantly across much of their historical range. Key threats include:

• Habitat degradation resulting from coastal development, dredging, pollution and climate-related events such as cyclones.
• Fishing-related mortality, especially entanglement in gillnets and trapping in ghost nets.
• Traditional hunting, which remains culturally significant in some regions but compounds pressure on depleted populations.
• Vessel strikes, particularly in areas with heavy boating activity.
• Low reproductive rates, with long intervals between births limiting population recovery.

Legal protections exist in many jurisdictions, and international agreements such as CITES restrict trade in dugong-derived products. Conservation initiatives focus on habitat protection, community-led stewardship, monitoring of populations and the regulation of hunting. However, fragmented populations and ongoing environmental degradation pose persistent challenges.