A rare Irrawaddy dolphin found dead in the waters of Calabanga, Camarines Sur, has suggested to scientists a rich marine biodiversity corridor yet to be discovered and explored in the eastern side of the Philippines.

Named “Calab” by the Bureau of Fisheries and Aquatic Resources (BFAR) and the Philippine Marine Mammals Stranding Network (PMMSN), the dolphin, an otherwise healthy female juvenile, was found tangled in a fisherman’s net in San Miguel Bay off Calabanga last Aug. 16.

Scientists who performed a necropsy on the sea mammal found its stomach full of undigested fish, indicating that it died relatively suddenly and unexpectedly.

“Calab’s death is an unfortunate incident, but it has paved the way to learning more about these rare and beautiful creatures,” said Lemnuel Aragones, the president of PMMSN and a professor at the Institute of Environmental Science and Meteorology (IESM) at the University of the Philippines Diliman.

First sighting in Bicol

Aragones said it was the first time an Irrawaddy dolphin was found on the Pacific side of the archipelago. There have been two other sightings of the species in Malampaya Sound, Palawan, and in the Iloilo-Guimaras Strait. 

Irrawaddy dolphins (Orcaella brevirostris) are among the world’s most endangered dolphin species and are on the Red List of the International Union for Conservation of Nature. They are considered critically endangered by the Department of Environment and Natural Resources, and have a scattered range of distribution, with most populations found in South and Southeast Asia. 

According to marine experts, Irrawaddy dolphins  are euryhaline, or with a high tolerance to various levels of salinity, which enables them to live in areas where salty seawater and freshwater meet.

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Necropsy results

Aragones identified Calab’s species from photos sent by the BFAR regional office and the Calabanga municipality. A fisherman in Barangay Bonot-Santa Rosa in Calabanga had reported the dolphin caught in his net to local authorities.

The body was brought to the Marine Mammal Research and Stranding Laboratory in IESM where, coincidentally, a nationwide training seminar on “Medical Management of Stranded Marine Mammals” was being held last Sept. 5-6. Aragones and his colleagues took the opportunity to conduct the necropsy for the educational benefit of the attendees.

The young dolphin measured about 180 centimeters long and 102 cm at its widest point. It weighed between 75 and 95 kilograms.

Irrawaddy dolphins usually have gray or dark blue backs and pale bellies. They closely resemble Australian snubfin dolphins, which have three colors, and beluga whales, which do not have dorsal fins.

“Calab might have been able to increase the survival chances of marine mammals that will be stranded on shores in the future,” Aragones said.

Habitat threats

Scientists have yet to track the populations of Irrawaddy dolphins that make their habitats off the provinces of Palawan and Iloilo and the Bicol Region. Aragones suggested that the species might have been present there since prehistoric times, before humans arrived in the archipelago, and possibly even before humans existed at all, when environmental conditions were likely optimal for widespread migration.

“Basically, the populations have been there for a very long time. We just didn’t know to look for them,” he said. Despite needing air to breathe, dolphins generally spend as much as 95% of their lives underwater, enabling them to elude discovery.

The Irrawaddy dolphins in Malampaya and San Miguel Bay were spotted in estuaries near local rivers, while those in the Iloilo-Guimaras Strait were in coastal waters. San Miguel Bay is home to different species of whales and dolphins, and even dugong (sea cows).

Dynamite blasting and other illegal fishing practices, overfishing and poorly planned construction of bridges and other infrastructures disrupt marine environments and threaten biodiversity. The future of species like Irrawaddy dolphins may be bleak, amid unsustainable conservation efforts.

Marine biologists and conservation groups have expressed concern, particularly over the proposed 43-kilometer bridge linking Iloilo, Guimaras and Negros Occidental that may disturb the habitat of Irrawaddy dolphins in the area. 

With the recent discovery of Calab, Aragones is eager to know more about the Irrawaddy dolphins in San Miguel Bay. This is proof, he pointed out, that there is still so much to be discovered in the Philippines’ richly biodiverse waters. 

A deeper inquiry into the recent stranding of the dolphin is in progress, according to Aragones. His team of marine mammal scientists and local BFAR personnel are scheduled to visit San Miguel Bay, aiming to estimate the population of the species and possibly define their habitats.

“That’s where researchers like us come in … to explain the importance of these animals,” Aragones said. “We must spread awareness that these animals exist and that they are endangered, so that we can [put in place] regulations that will protect not only the animals that we know, but also those that have yet to be discovered.” 

Shedy Masayon is a graduate of communication and media studies at the University of the Philippines Visayas. She is training as a science communicator at the UP Diliman College of Science. —Ed.