Marine Mammals of South-east Asia: A Biodiversity Treasure Under Threat

South-east Asia, often celebrated as one of the world’s marine biodiversity hot spots, is home to an astonishing array of marine life, including over 3,000 species of fish and 600 types of coral. Among its most captivating inhabitants are marine mammals—whales, dolphins, porpoises, and dugongs—that roam the region’s warm, nutrient-rich waters. From the elusive dugong grazing on seagrass beds off Singapore to the majestic humpback whale sighted near Malaysia’s Pulau Redang, these creatures are not just a spectacle for nature enthusiasts but also vital indicators of ocean health. Yet, as sightings increase, so do the threats they face, casting a shadow over their future and, by extension, the region’s marine ecosystems.

A Diverse Marine Menagerie

The waters of South-east Asia host an impressive variety of marine mammals, each adapted to specific ecological niches. Humpback whales, known for their haunting songs and massive size—growing up to 18.3 metres and weighing as much as five buses—migrate to the coasts of the Philippines and Thailand between October and January for mating and reproduction. A notable sighting off Pulau Redang in September 2024 marked the first recorded appearance of the species on Malaysia’s east coast, a testament to the region’s enduring allure for these giants.

Sperm whales, with their enormous brains and distinctive block-shaped heads, are another iconic species, often spotted off Malaysia, Indonesia, and Brunei between April and July. Tragically, their presence is sometimes marked by loss, as seen in 2015 when a sperm whale carcass washed ashore near Singapore’s Jurong Island, likely killed by a ship strike. Its skeleton, nicknamed “Jubi Lee,” now hangs in the Lee Kong Chian Natural History Museum as a poignant reminder of the perils these animals face.

Smaller but equally fascinating are the region’s dolphins and porpoises. The Irrawaddy dolphin, with its rounded face and slow, deliberate movements, inhabits estuaries and coastal waters across Vietnam, Cambodia, and Myanmar. Critically endangered in parts of the Mekong River, where fewer than 85 individuals remain, this species is on the brink of local extinction. Meanwhile, the Indo-Pacific humpback dolphin, often sporting a unique pinkish hue in Asian waters, can be found from Singapore to Vietnam, though its population is listed as vulnerable.

Perhaps the most enigmatic of all is the dugong, affectionately dubbed the “sea cow” for its seagrass diet. Found in shallow coastal waters across the region, including Singapore and the Philippines, dugongs play a crucial role in maintaining seagrass meadows, which are vital to marine ecosystems. As Sirius Ng, a PhD student at the National University of Singapore (NUS), notes, dugongs even aid seagrass germination through their digestive process, dispersing seeds as they feed.

Why Marine Mammals Matter

The presence of marine mammals in South-east Asia’s waters is more than a point of pride; it signals the health of the region’s marine environments. Marcus Chua, a mammal researcher at NUS, explains that their ability to thrive indicates that local habitats can sustain large predators like whales or herbivores like dugongs. Conversely, their decline would suggest an ecosystem in distress. Dr Louisa Ponnampalam, co-founder of the Malaysian conservation group MareCet, puts it starkly: “If we lose them, it means the sea around us is no longer healthy, and we humans rely on the sea for so much, whether we realise it or not.”

Marine mammals also hold cultural significance across the region. In Vietnam, whales are revered as deities, with elaborate funerals held for those found stranded. In Chinese mythology, the now-extinct Baiji dolphin was seen as the reincarnation of a tragic maiden, while bones of Indo-Pacific humpback dolphins were offered in temples for protection at sea. These stories underscore a deep historical bond between communities and the ocean’s giants, a connection that modern conservation efforts must honour.

Mounting Threats to Survival

Despite their importance, marine mammals in South-east Asia face a barrage of threats, many of which stem from human activity. Marine litter, including plastic debris and discarded fishing gear, poses a lethal risk. Ingestion can cause internal damage, while entanglement in nets or ropes can lead to injury, starvation, or drowning for air-breathing species like dolphins and whales. The Food and Agriculture Organisation of the United Nations estimates that over 500,000 marine mammals are accidentally caught in fishing operations globally each year, a statistic that hits close to home in South-east Asia’s busy waters.

Ship strikes are another critical danger, particularly in high-traffic areas like the Malacca Strait near Singapore. Chua notes that an average of 30 whales, dolphins, and porpoises are killed annually worldwide by vessel collisions, a risk exacerbated in the region’s crowded shipping lanes. Dugongs, which surface frequently to breathe, are especially vulnerable, as are whales navigating these waters.

Underwater noise pollution from shipping, industrial activities, and military sonar adds to the peril. Sound travels faster and farther underwater than in air, disrupting marine mammals that rely on acoustic signals for communication, feeding, and navigation. Dr Ponnampalam highlights that such noise can cause hearing loss or behavioural changes, yet it remains unrecognised as an official threat in South-east Asian policy frameworks.

Coastal development, including land reclamation and dredging, further fragments habitats, isolating populations and limiting their access to feeding or breeding grounds. Even well-intentioned activities like whale watching can stress animals if not conducted responsibly. Dr Ponnampalam advises maintaining a distance of at least 100 metres and reporting unethical practices, such as tours that restrain animals, to authorities.

The Road to Conservation

As International Marine Mammal Protection Day on 19 February approaches, experts are calling for urgent action to safeguard these species. Dr Ponnampalam stresses the need for more resources to support research in South-east Asia, where funding and capacity often lag behind global standards. Potential areas of study include bioacoustic research to assess noise pollution’s impact, genetic studies to track population diversity, and ecological surveys to map distribution and behaviour. Understanding local communities’ cultural and socioeconomic ties to marine mammals is equally vital for crafting effective conservation strategies.

Practical measures can also make a difference. Enforcing vessel speed limits in collision-prone areas, as suggested by Chua, could reduce ship strikes. Stricter regulations on fishing practices and marine litter, coupled with public awareness campaigns, might mitigate entanglement and pollution risks. For species like the Irrawaddy dolphin, targeted protection of critical habitats such as the Mekong River is essential to prevent further declines.

South-east Asia’s marine mammals are not just a natural wonder; they are a barometer of the region’s environmental health and a link to its cultural heritage. Their survival hinges on a collective commitment to address the threats they face, from plastic pollution to habitat loss. As sightings of humpback whales and Bryde’s whales increase—nine of the latter have been logged in Thai waters since November 2024—there is hope that with concerted effort, these creatures can continue to grace the region’s seas. But the window for action is narrowing, and the stakes could not be higher: lose these guardians of the deep, and we risk losing the very oceans that sustain us.