KOCHI: The dwindling stocks of sardines along Kerala's coast have affected not only the livelihood of fishermen but also the Indian Ocean humpback dolphins, a species listed by the International Union for Conservation of Nature as endangered.These dolphins are usually sighted in bays, lagoons and estuaries. The decline of dolphin sightings in the Kochi estuaries has caused concern among green activists. According to them, around 60-80 dolphins could be sighted in the Kochi coastal waters per day three decades ago. But hardly 10 dolphins are seen nowadays.
Researcher Divya Panicker, who conducted a study on 'Indian Ocean humpback dolphins estuary use-patterns in Kochi harbour' said excessive human activity and industrial effluents flowing into the sea are threatening the existence of the species. The humpback dolphin lives close to the shore in waters up to about 20 metres deep.
One of the reasons for the falling numbers is the lack of food resources in the sea, said CMFRI principal scientist V Kripa. These mammals mainly feed on sardines, known as forage or prey fish. “The biological status of this species is distinct and it takes around 10 years to sexually mature. Since they are only a few in number, any threat can have a great impact. Therefore, they are considered endangered,” she said.
The rather declining mudbank formations due to over-fishing and mechanised trawling are affecting these mammals to a large extent. The temperature variations due to climate change and industrial pollution are some of the factors that hamper their existence. The decreasing trend of the salinity in the water is also a major concern.
“Mammals are more affected by sound pollution rather than water pollution, therefore studies must be conducted in those areas,” said Kripa.Sound pollution can disrupt their path and it leaves them losing their balance and get strangled on the way.The changes in the food chain are moreover affecting organic life beneath the waters. The eutrophication and increase in the amount of metallic or chemical contaminations in the backwaters is having an ill effect on these mammals, said CUSAT School of Marine Sciences head of department S Bijoy Nandan.
The destruction of mangroves is also affecting the native species of the regions. Clogging of canals with plastic and other waste are increasing at an alarming rate. The abundance of silt, copper and lead can lead to changes in the tropic structure.Dredging activities may cause navigation difficulties among the dolphin, which makes them drift from their path. There are no quotas fixed for dredging activities. Quotas must be made for dredging in order to reduce its impact on the species underneath. Marine Protected Areas must be recognised in the Cochin estuaries. The Ramsar Convention of 2002 has recognised the threat that the species undergo in the backwaters, but not much effort was taken by the state in doing the needful, said Nandan.
“The National Biodiversity Authority and state biodiversity authorities are becoming more political these days, which leads to all sorts of negligence from their part," he added.Kerala Matsya Thozhilai Aikya Vedi president Charles George said climatic changes and unregulated trawling practices are the reasons for the depletion of sardine stocks. "From the harbour to Thevara bridge, fishing activities have been restricted to protect dolphins. If there is a fall in dolphin sightings in these particular areas, then it is a red signal,” he said.