Marine Mammal Stranding: Myth, Mystery and Facts
05 Sep, 2017 · 5355
Dr Vijay Sakhuja analyses the phenomenon of increasing numbers and incidents of marine mammals getting stranded ashore or washing aground in India
The stranding of marine mammals along India’s east coast astride the Bay of Bengal and west coast overlooking the Arabian Sea has been a recurring phenomenon. In 2016, 80 short-finned pilot whales were found stranded on the sand along the east coast. The largest stranding on the east coast took place off the Tuticorin coast in 1973 when 147 whales were found on the beach.
In August 2017, 18 feet long whale shark with a circumference of 10 feet and weighing nearly 3.5 tons washed up on Pamban beach in Tamil Nadu. The necropsy revealed a plastic spoon in the whale shark's digestive system. The state wildlife authorities cautioned that plastic waste was harming the marine eco-system and that marine species are unable to differentiate between floating plastic and prey. Unlike the Pamban stranding, the 47-foot whale discovered on the beaches of Ratnagiri district on the west coast in 2016 was successfully rescued and pulled into deeper waters.
However, there have been at least 16 and 20 incidents of whale mortality along the west coast in 2015 and 2016 respectively. These figures are alarming given that between 2001 and 2014, whale deaths never exceeded four.
Myth and Mystery
Stranding of marine animals along sea shores is not a new phenomenon. It happens across the globe on a regular basis but been part of myth as also an issue of mystery. Mammal stranding has baffled humankind since ancient times. Aristotle noted that it is not known why they run aground but asserted that “this happens when the fancy takes them and without any apparent reason.” The myth associated with the stranding of mammals is in the belief that Romans thought ‘stranding was a whale’s punishment for offending Neptune, the god of the seas’.
However, with advancements in science, it is now known that there are a number of natural conditions including the movement of tectonic plates underwater resulting in shifts in magnetic field causing disorientation among marine animals. Also, man made circumstances result in mass stranding, even ‘suicides’, and these arise from marine pollution, use of Sonars by navies, presence of plastics in the oceans, and other commercial activities including offshore infrastructure activities.
Facts: Marine Litter and Underwater Noise
There are at least two important reasons that can be attributed to the stranding of marine mammals along the shores. First, the growing menace of plastics in the oceans and seas has been identified as one of the important causes affecting health of marine life at sea as also the marine ecosystem. Over the past seven decades, plastic has emerged as a cheap and lightweight material for the packaging, auto parts and domestic durables industries. The annual global production of plastics is pegged at 300 million tons, and half of it is ‘single use’. Ironically, ‘disposable’ lifestyle habits and practices, poor plastic waste management and disposal techniques, lack of awareness among the public, and absence of serious policies on plastic use by governments including weak implementation mechanisms have resulted in nearly 8 million tons of plastic dumped annually into the oceans. Nearly 60 to 90 per cent of marine litter is plastic-based in the form of straws, plastic bags, fishing gear, food and beverage containers, bottles, and large pieces of plastic made auto parts, making these are the most common forms of plastic pollution in the oceans.
Evidence exists of presence of plastic in mammals amid fears that over 50 per cent of sea turtles have consumed plastic. A necropsy of the sperm whale that beached and got stranded on Germany’s North Sea coast in 2016 found fishing gear and an engine cover inside the stomach. Scientists believe, among many other causes for stranding of the sperm whales, the ingested marine litter, can potentially “cause physical damage to their digestive systems” and “may eventually give the animals the sensation of being full and reduce their instinct to feed, leading to malnutrition.”
Second, marine noise generated by shipping and fishing trawlers, offshore exploration, laying of pipes and fiber optic cables as also use of Sonar by warships results in casualties in marine mammals. A recent study by the Indian Maritime Foundation, titled 'Impact of Maritime Security Policies on Marine Ecosystem' has observed that underwater noise in excess of “120dB can cause discomfort to these [marine] species, more than 170dB can cause serious internal injuries, bleeding and even hemorrhages, and noise beyond 200dB can cause instant death.”
Powerful Sonar transmissions can potentially lead to internal bleeding in mammals causing damage to ear and brain tissues, resulting in disorientation or death of mammals. There is also a belief that whales may even misunderstand Sonar waves as an attacker, and cause panic driving them towards shores.
In the US, in 2016, the Ninth US Circuit Court of Appeals in California observed that a 2012 regulation that allowed the US Navy to use low-frequency active sonar for training and testing violates the Marine Mammal Protection Act. The National Marine Fisheries Service (NMFS) has now announced stringent regulations on Sonar transmission and prohibits pulses of 180dB or more by the US Navy within 14 miles of any coastline, or within 0.6 miles of marine sensitive areas.
There is little doubt that marine litter in the form of plastics, and pollution due to human activity, are causing enormous damage to marine mammal and the marine ecosystem. While the global focus is on managing plastic pollution on land, marine litter can affect the food chain of the marine habitat as also human beings. It takes thousands of years for plastics to decay and toxins from the plastics have now begun to enter the human food chain and threatening health.
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