Why do whales wash ashore?

Image shows a whale who was washed ashore and its autopsy revealed the huge amount of plastic trash it had consumed.
Why do whales wash ashore?

-Ameya Paleja

Last month, about 100 whales have washed ashore along the coastline of Tiruchendur, in the southern state of Tamil Nadu. While locals in the area were successful in pushing back 36 of these whales using various methods, 45 of these creatures succumbed on the shore. Just a couple of weeks after this incident, a 30-foot whale has washed ashore on the western coast. Although we still await formal reasons for these incidents, you might have come across a lot of theories put out by experts as well on non-experts through various media channels as to why these whales might have reached the shores. Through this post, however, we will look at well-investigated reasons why these sea creatures might leave the sanctity of their homes and travel to shallow waters.

We have heard many reports of how the introduction of plastic waste into water bodies has impacted marine and aquatic life. Fishes and aquatic birds have been affected alike by ingestion of plastic compounds that are unnatural to their surroundings and have been introduced purely due to human methods waste management. But ingestion of plastic is not the sole cause of concern for marine ecologists.

Cords and ropes made out of hemp and cotton that were traditionally used for all marine activities have now been replaced by nylon and other synthetic materials. These materials have a longer decay cycle as compared to hemp and cotton Wore out fishing nets that are discarded in the sea are still capable of trapping fishes and other sea creatures and often lead to severe injuries. Other causes of losses to marine life due to plastic have been summarised in this review by Murray Gregory.

Decompression sickness:
The study of 14 beaked whales stranded on Canary islands in 2002, revealed that the whales suffered from acute tissue damage caused due to decompression sickness. In this sickness, dissolved gases in the blood, such as oxygen, carbon dioxide etc. leave their dissolved state and rise in the form of bubbles within the body as a result of sudden depressurization, a phenomenon that is commonly observed in divers or astronauts doing spacewalks.

Image shows a 12.5 m long southern right whale that died as a result of propeller hit washed ashore at Rio Grande do Sul in Brazil in October 1993.
Evidence for decompression sickness comes from the tissue damage caused due to gas bubble lesions, however, the exact cause of decompression was not determined. The study published in Nature in 2003 accused naval activities in the region and the use of SONAR for mass strandings in this region after which a SONAR ban was imposed in 2004 and an almost a decade of observations showed no mass stranding events in the region after the ban.

Vessel collisions:
As traffic over the oceans as increased as a result of the shipping and tourism industry, larger aquatic animals such as whales have been affected largely by incidents of vessel collisions. Fishes usually die as a result of ship-related incidents or are traumatically injured.

Although vessel collisions have drawn many fish species such as Indo Pacific humpback dolphin, Irrawaddy dolphin, finless porpoise and many other whales in the Northern Hemisphere, researchers strongly believe that vessel collisions are still under-reported and available data is not revealing the true picture. Dinoflagellate toxin

14 Whales were washed after shearing near Massachusetts in the US in the year 1987. Investigations led by Charles Mayo at the Centre for Coastal Studies revealed that the whales died after consuming mackerel fish that contained dinoflagellate toxin called saxitoxin (STX). 

The toxin is usually produced by dinoflagellates and certain bacteria to protect themselves from overconsumption. It is also responsible for paralytic shellfish poisoning in humans. Since dinoflagellates are present in oceans worldwide, there are likely to be more instances of poisoning, which occur but are not investigated in sufficient detail.
Ameya Paleja: 
A Molecular Biologist by day and a blogger by night, I like to write about Genetics, Microbes and Future at my blog Coffee Table Science. I support the development of 'greener' sources of energy and believe that solar power is the answer to all our energy needs.