Dolphins may have made an appearance along Mumbai’s coastline earlier than usual this year.
Conservation biologist and Malabar Hill resident Darshan Khatau, who has been documenting the movement of the Indian Ocean humpback dolphin annually for the last four years, said sporadic sightings of dolphins were usually seen from the second or third week of December annually up to last week of May (just before the monsoon season).
“This year, they arrived unusually early during the third week of November,” said Khatau. He spotted three individuals off Malabar Hill from November 15 and 16 onwards and has been regularly photographing them since. “In the previous years, the maximum number of individuals has been 12 in one pod. The early arrival could be due to shifts in ocean currents leading to more prey availability along the Mumbai coast.”
Last Wednesday, a video was circulated on social media by environmentalist Zoru Bhathena of an Indian Ocean humpback dolphin spotted off Juhu beach.
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Marine biologists concurred with Khatau’s finding but said it cannot be verified as no official survey or study to monitor the population or behaviour of this species was carried out along Mumbai so far.
“The Mumbai coast is used by Indian Ocean humpback dolphins (Sousa plumbea) for biologically important activities. Darshan has been observing foraging, socialising and mating in the area he observes. It is possible that their early arrival is related to oceanographic characteristics – currents, productivity, and prey availability,” said Dr Dipani Sutaria, senior research fellow, who has undertaken extensive research in cetaceans (whales, dolphins and porpoises) along the west coast of India.
Dr Baban Ingole, visiting scientist, National Centre for Polar and Ocean Research under the Ministry of Earth Sciences and former chief scientist, National Institute of Oceanography, said, “Since these are observations over four years, I certainly support it, and this may be happening across other areas along the west coast too, but we must understand the specific reason why this might be happening.”
Ingole explained that from April onwards till early November, fishing activities had been at its lowest due to the Covid-19 pandemic and associated lockdown followed by the southwest monsoon (when the annual fishing ban is in place). “2020 was lean for fishing in at least over 10-15 years. There is enough evidence to suggest prey must be abundantly available along the coast. This means dolphins and other predators had enough food as compared to previous years. However, we must assess it now as the fishing activity picks up. Thus, we could expect more such sightings along the west coast,” said Ingole.
The state fisheries department said fishing was practically zero during the lockdown followed by monsoon. From August onwards to the first week of November, it was just about 10% of what it is annually during this period. “This was because a large number of workers that generally come from Ratnagiri (as crew) avoided coming to Mumbai due to the pandemic. They arrived post Diwali, and since then, fishing activities has been about 40-45%,” said Rajendra Jadhav, joint commissioner, Maharashtra fisheries department.
Protected under Schedule I of the Wildlife Protection Act, 1972, and listed by the International Union for Conservation of Nature as vulnerable, the Indian Ocean humpback dolphins have sporadic distribution, and are found in localised areas mainly in shallow waters very close to the shore (less than 20m deep, less than 1.5km from the shore, and around river mouths or estuaries), according to the Marine Mammal Research and Conservation Network of India. This dolphin species primarily feeds on fish such as mackerel, mullet, sardines and pomfret.
“Since this is identified on the basis of live examples, it is an interesting identification. It could be due to changes in ocean currents which carry their feed material in plenty, and also may be favourable for their movement at the moment. Also, the Covid-19 associated lockdown may have improved water quality closer to the coast,” said E Vivekanandan, emeritus scientist at the Central Marine Fisheries Research Institute.
Vivekanandan however warned that with an increase in infrastructure projects planned along the Mumbai coast, there was an immediate need for a population estimation of the marine species. “It will help strengthen conservation measures and provide crucial information about the species,” he said.
The state mangrove cell said they were focusing on occurrence and genetic studies related to Indian Ocean humpback dolphins along all coastal districts of Maharashtra, including Mumbai. “This has been proposed under our action plan for oceanic dolphin conservation under the Centre’s Project Dolphin program, which has been submitted to the state chief wildlife warden for approval. We hope such studies will help improve the understanding of this species,” said Virendra Tiwari, additional principal chief conservator of forest (Mangrove Cell).