Risso’s dolphins are found across the world’s oceans. They prefer, as per NOAA, mid-temperate waters of the continental shelf and slope between 30-45 deg latitude. They are there in the depths of 3,300 feet as well as at the surface. They are extraordinary, out-of-the-world yogis, in that they can dive 1,000 feet and hold their breath for 30 minutes.

They have now been found in Indian waters. Risso’s Dolphin—Grampus griseus—has been sighted for the first time in the Bay of Bengal inside the Indian Exclusive Economic Zone (EEZ), according to a June 2025 study. The study was published in Marine Mammal Science.

In the northern hemisphere, Risso’s dolphins’ range includes the Gulf of Alaska, Gulf of America, Gulf of Mexico, northwest Atlantic from Florida to Newfoundland, Azores, Norway, Japan, Russia, and the Red Sea. In addition, they are known to inhabit the Mediterranean Sea, are rare in the Black Sea, and do not appear to inhabit the Persian Gulf and some other very shallow, enclosed bodies of water. In the southern hemisphere, their range includes Argentina, Australia, Chile, South Africa, and New Zealand.

“It was exciting to record Risso’s dolphin in our waters,” says Yosuva Mariasingarayan, the lead author and a marine biologist with Centre for Marine Living Resources and Ecology (CMLRE), Kochi.

The paper gives a baseline information on the distribution of Risso’s dolphins: the species are spread along continental slopes in both nearshore and offshore areas (100–3100 m). The distribution pattern suggests that the area between 16 deg N and 18.5 deg N may be an important zone for this species.

The Indian EEZ comprises five geographical zones: northwest (northeastern Arabian Seas—NEAS), southwest (southeastern Arabian Sea—SEAS), southeast (southwestern Bay of Bengal—SWBOB), northeast (northwestern Bay of Bengal—NWBOB), and Andaman and Nicobar waters (A&N) . The survey, conducted from August 2022 to March 2024, includes the area of the exclusive economic zone (EEZ) of India along the eastern Arabian Sea, western Bay of Bengal, and Andaman Nicobar waters (A&N).

A total of 120 species of marine mammals are known worldwide. In Indian seas, 26 species of cetaceans and a single species of sirenian (Dugong dugon) have been documented.

India’s initiation of marine mammal monitoring programmes has been influenced, in part, by international trade regulations. In 2016, the United States implemented provisions under the Marine Mammal Protection Act (MMPA), requiring that countries exporting fish and fishery products demonstrate that their fisheries do not adversely affect marine mammal populations. Compliance with this regulation necessitates the assessment and monitoring of marine mammal stocks, thereby prompting India to strengthen its survey and data collection efforts.

Furthermore, the Indian Ocean Tuna Commission (IOTC) requires its member countries to report on the status of tuna and tuna-like species, along with associated ecosystem impacts, including marine mammal interactions. This requirement has further emphasised  the need for systematic monitoring and reporting frameworks in India.

In response, the central government has initiated the Marine Mammal Stock Assessment in India under the Pradhan Mantri Matsya Sampada Yojana (PMMSY). The Fishery Survey of India (FSI) plays a central role in conducting offshore surveys within the EEZ in collaboration with ICAR-Central Marine Fisheries Research Institute (CMFRI), ICAR-Central Institute of Fisheries Technology (CIFT), and MPEDA-NETFISH. Network for Fish Quality Management & Sustainable Fishing (NETFISH) under the Marine Products Export Development Authority (MPEDA) collects real-time marine landing data from 100 harbours.

These are part of a broader Blue Revolution framework aimed at ensuring sustainable development of India’s fisheries sector. The work has been operational from 2021, pioneered by R. Jeyabaskaran, marine mammal researcher and a former director-general of FSI.

Mariasingarayan has 142 days of sea-going experience aboard FSI’s survey vessel Matsya Drushti (Chennai base). During his time at sea, communication with the shore was not possible due to the lack of mobile connectivity. His experience at sea, breathing fresh ocean air and observing dolphins and whales was truly mesmerising, he says.

India’s coastline stretches for 11,099 km, and an EEZ that extends to 200 nautical miles, covering 2.37 million square kilometres. It presents unique challenges in surveying marine life forms. India also lacks “broad-scale visual and acoustic surveys to estimate their population abundance of marine mammals”.

Just as marine mammals are beset by problems such as bycatch, gill nets, trawlers, research institutes too have their own problems. There are not enough taxonomists and biologists; more staff are recruited on a temporary basis than as tenured appointments.

Researchers like Mariasingarayan, however, do survey the seas. Their vessels are equipped with instruments such as GPS navigators, echo-sounders, thermometers, barometers, and anemometers. From atop raised platforms on the vessels, researchers use binoculars and cameras to sight the mammals along a series of transects within demarcated areas. The method yields estimates of marine mammal species diversity and abundance.

Advanced nations use drones, flights, bioacoustics to keep their surveys and conservation in prime. The need for Passive Acoustic Monitoring (PAM) in India has been discussed, in this report.

Passive acoustic monitoring (PAM) is used to measure, monitor, and determine the sources of sound in underwater environments, enabling scientists to eavesdrop on the acoustic behaviour of marine whale song, fish chorusing, snapping shrimp, natural abiotic sounds, wind, earthquakes and human generated sounds, cargo vessels.

Mariasingarayan wishes to see India having an institute dedicated solely to marine mammals for there are many more species waiting to be discovered in the depths of oceans.