A new scientific study has revealed a worrying rise in baleen whale strandings along India’s southwest coast, pointing to growing threats to marine ecosystems and fisheries in the region.
The research, published in ScienceDirect and led by R Ratheesh Kumar, Senior Scientist at the Central Marine Fisheries Research Institute (CMFRI), analysed two decades of data (2004–2023) and recorded 33 baleen whale strandings. Alarmingly, 30 of these incidents occurred after 2014, underscoring a sharp escalation in recent years.
Baleen whales are a group of 14 species, including the blue, bowhead, right, humpback, minke, and gray whales. They have a filter-feeding system inside the mouth called baleen—the same protein found in human fingernails and hair.
Between 2014 and 2023, Kerala reported the highest number of strandings (16 cases), followed by Karnataka (10) and Maharashtra (4). In 2023 alone, nine whales were stranded along the southwest coast, mostly during August to November. Kerala accounted for five of these, while Karnataka reported three and Maharashtra one.
The study attributes whale strandings to a complex mix of ecological, biological, and human-related factors.
The study noted that “these events often reflect disruptions in ocean systems, including prey distribution shifts, harmful algal blooms, and climate-driven variability.” Additional factors included “meteorological events, acoustic/communication disturbances, disease outbreaks, sensory malfunctions, and anthropogenic pressures like vessel strikes, entanglement, habitat degradation, and pollution.”
Whale survival depends on plankton productivity, fishes that consume planktons are food for the whales. Productivity is measured based on chlorophyll biomass. Baleen whales are usually found in highly productive areas, as there will be a lot of other smaller fishes. These productive zones are mapped using chlorophyll indicators.
Researchers also observed that “environmental anomalies, including elevated chlorophyll-a concentrations, harmful algal bloom events, and abrupt changes in Sea Surface Temperature (SST), may precede or coincide with increased stranding incidences.” The paper stressed the importance of developing “predictive indicators of stranding risk.”
In addition, ship traffic, noise pollution, and vessel strikes are emerging as major risks, particularly in Karnataka, where increased vessel movement may have contributed to three recent strandings. Unlike toothed whales (Odontocetes), baleen whales rely on low-frequency sounds, making them highly vulnerable to acoustic disturbances from ships.
Other contributing factors include meteorological events, disease outbreaks, sensory malfunctions, entanglement in fishing gear, and pollution-related habitat degradation.
R Ratheesh Kumar, the lead author of the paper, told TNM that “In the last 10 years, stranding numbers have increased tenfold. Whales migrate from north to south. During their migration, particularly during the monsoon season (August to November), marine fish production peaks. Sardines and anchovies become easy targets for whales. Possibly because of this, whales move closer to coastal regions, whereas usually they do not.”
He also added that turbulent monsoon conditions may interfere with whale navigation: “The turbulence during monsoons might disrupt their echolocation ability. At such times, they may not be able to detect vessel movements, leading to an increase in vessel strikes, which cause their deaths. During this season, winds converge along the Karnataka and Kerala coasts. As a result, whales that die in any part of the deep sea may get carried to the coast by these winds.”
S Bijoy Nandan, Senior Professor, Dept. of Marine Biology, Microbiology and Biochemistry, Dean, Faculty of Marine Sciences, at Cochin University of Science and Technology told TNM that heat stress in the ocean is a major factor causing imbalance in ocean ecosystems. “We can already see a major change in chlorophyll production. Heat stress is an important factor. Extreme heat events are happening, and we need to consider their impact. Warming is happening along with sea level rise. Around 0.8 to 0.9 degrees of temperature rise is being recorded in the ocean. Heat islands have been observed in the Indian Ocean,” he said.
In 2023 alone, “nine whale stranding events [were] recorded between January and December, with the highest number occurring in Kerala (5), followed by Karnataka (3) and Maharashtra (1).” All strandings happened “between August and November 2023.” Kerala reports came from Thrissur (2), Kozhikode (2), and Kasargod (1) districts, while Karnataka recorded three in Honnavar, Uttar Kannada district. In Maharashtra one incident was reported from Ratnagiri.
The study emphasised the vulnerability of baleen whales to shipping activity. “Three strandings recorded from Karnataka were supposed to be caused by the increased vessel movements or ship traffic in the region. Due to their reliance on low-frequency sounds and less specialized hearing compared to Odontocetes (toothed whales like, sperm whales, dolphins etc..), baleen whales are more vulnerable to ship noise, which may startle or disorient them, increasing the risk of vessel strikes.”
Bijoy Nandan also supported the study findings and said that the unwarranted release of greenhouse gases — carbon dioxide, methane, nitrous oxide — into the ocean is another factor that can cause harm to marine mammals. “This happens due to human activities such as burning fossil fuels, discharge of industrial waste, and pollutants.Incidents like the recent shipwreck and oil spill on the Kerala coast can also indirectly affect the marine ecosystem. Nanoplastics in the ocean are another major issue. Many studies have shown the presence of heavy metals and plastics inside marine mammals.”
“The Indian Exclusive Economic Zone hosts 31 marine mammal species, including six species of baleen whales such as the blue whale (Balaenoptera musculus) and humpback whale (Megaptera novaeangliae), making conservation efforts critical,” the study notes.
To improve response strategies, the CMFRI team calls for the development of region-specific predictive models tailored to tropical marine ecosystems, which differ significantly from those in temperate regions where most stranding research is currently concentrated.
A senior scientist, who sought anonymity as he works with the government, said, along with climate change the increase in interactions in sea water- vessel strikes, plastic dumping etc - have resulted in these strandings. “Climate change has intensified interactions, and vessel collisions have increased significantly. Fish availability has declined considerably. Even fishermen struggle to get enough fish, and whales face shortages in their regular feeding grounds. That is why they migrate. Climate change is also a major factor.”
Each reported stranding was systematically documented by CMFRI officials, who visited sites with handheld GPS devices recorded coordinates and decomposition stages of the whales.This standardised dataset, combined with satellite environmental data, is expected to reveal valuable patterns of when and where strandings occur.
Ratheesh Kumar said CMFRI began its first dedicated Marine Mammal Stock Assessment Project in 2021. “Though there have been multiple marine mammal projects earlier, this one was specific. CMFRI is the first to undertake this using a standardised methodology. We are following the Line Transect Distance Methodology,” he said, referring to a vessel-based survey method used to estimate populations.
In such surveys, vessels are used to travel up to 200 nautical miles in a straight line. “The next line will be 60 nautical miles away in the deep ocean, while in coastal areas the distance will be 12 nautical miles. We classify the area into two strata: the coastal stratum (0 to 12 nautical miles) and the oceanic stratum (12 to 188 nautical miles). This is how we conduct continuous vessel surveys,” he said.
International trade pressures were also a reason why the survey was undertaken. “In 2019, the US, where we exported the majority of our marine products, banned the import of wild-caught shrimp, citing that our boats did not use turtle exclusion devices. They imposed a blanket ban. India does not have laws to specifically protect marine life. Therefore, in order to export our marine products, we must assess the stock, strandings, and status of marine species. Only then can exports continue.”
Bijoy Nandan stressed on the immediate need of consistent mapping of marine life in India. “Unfortunately, there is no consistent mapping or data collection on marine life in India. We only study mammals that have been stranded. There may be many more deaths that go unrecorded. We have been suggesting remote-sensor-based mapping, drone-based evaluation, and biological mapping. Mapping should become a regular practice,” he said.