The mass stranding of more than a 100 whales and the death of at least 45 along a 15 km stretch on a Manpad beach in Tamil Nadu’s Tuticorin (or Thoothukudi) district presented a shocking spectacle on Tuesday. On Wednesday, the Central Marine Fisheries Research Institute (CMFRI) confirmed the death of at least another 12 whales. Interestingly, Tuticorin had witnessed a similar beaching 40 years ago, and the reasons are no clearer now.
Whale stranding is not uncommon and has been recorded since 300 BC. While dead individuals often naturally wash up ashore, the phenomenon of mass beaching still baffles scientists.
Typically, whales living in large social groups — such as the pilot whales that beached on Monday and Tuesday — are more susceptible to mass beaching. A pod (a group of marine mammals) can strand itself by following a disoriented leader or volunteer into shallow waters in a suicidal rescue mission if a member accidentally beaches itself.
Other ‘natural’ causes for whale beaching include following prey-rich water currents towards land or panicking at the presence of a mega predator such as a killer whale. Scientists also blame gently sloping shorelines that can deceive whales dependent on echolocation for navigation.
Active SONAR (sound navigation and ranging) — low-frequency sound released under water to detect marine vehicles — can have a similar or worse impact. The sound waves can cause internal bleeding in ear and brain tissues, killing or disorienting whales which may end up stranded. Some scientists also argue that whales may interpret the SONAR sound as an approaching predator, triggering a panic reaction and subsequent beaching.
Climate change or unnatural weather phenomena can affect whales. In one recorded event, after a strong El Nino in 1982-83, a resident population of short-finned pilot whales apparently disappeared from the areas along southern California.
In fact, even though the animals are found in the deep, warm waters of the Indian, Pacific and Atlantic oceans, short-finned pilot whales are known for frequent stranding. Their pods of up to 50 animals form ranks that can stretch for over a kilometre. This may explain how dozens beach themselves across several kilometres but it is not clear why they approach shallow waters.
In India, the first recorded beaching of short-finned pilot whales dates back to 1852 when a pod was stranded near Kolkata. Tuticorin also witnessed a mass stranding of 147 animals in 1973. Repeated beaching in one area may suggest a flat slope — a drop of mere 5-17 metres in 3 kilometres from Manpad beach, for example — or a current factor unique to the shoreline. Then again, there has been no mass beaching at Tuticorin since then, until Monday.
So far as the role of SONAR is concerned, it may be worthwhile to note that the last stranding in Tuticorin occurred not long after the 1971 war that might have necessitated intense and prolonged scanning of these waters.