Thiruvananthapuram: Increasing number of deaths of marine mammals and stranding of endangered whale species along the Kerala coast in recent months, apparently due to collision with ships, has highlighted the need to develop appropriate mitigation measures, a study has said.
In the past few months there have been reports of at least a dozen deaths of marine mammals along the coast. In addition to that, four whales stranded in 2010 and this year were identified as Bryde`s whale, an endangered marine species, A Biju Kumar, Head of the Department of Aquatic Biology and Fisheries, Kerala University, said.
Marine mammal mortality due to fishing operations was identified as a major threat to their population and this was true with regard to death of dolphins and porpoises in Kerala coast, Kumar, who conducted a study on the issue, said.
However, he said many of the deaths and ship strikes on mammals were not properly documented and identified. The high number of reported whale strandings in the past few years seems to indicate that the frequency of these events have increased, he said.
While globally anthropogenic encroachments such as contaminants and intensive sound disturbances, which derange the natural behaviour of the whales, have been considered to be a cause, along the Indian coast the primary reason for the killings could be collision with ships, he said.
Several whales stranded were found with serious injuries, probably due to collision with propellers, he said.
"Ship strikes can significantly affect small populations of whales, and in areas where special caution is needed to avoid such events, measures to reduce the vessel speed may be beneficial," he said.
Although information suggests that collisions between ships and whales were more common than previously thought, no attempt has been made to compile information on frequency of such collisions, Kumar said.
There are about 30 species of marine mammals in Indian coastal waters, including whales, dolphins, one species of porpoise and a variety of sea cow, he said.
Several marine mammals are vulnerable or endangered as they were traded for meat, ivory and fur. Many species were protected from commercial use, yet they receive less attention than land mammals such as the tiger and lion, Kumar said.
"In the absence of any dedicated survey to assess the abundance of marine mammals in Indian waters, we have no indication of their numbers, notwithstanding their population trends".
Kumar said many fishermen use the cues from dolphins to catch fish, as they chase large shoals of fish.
"While the Indian Wildlife Protection Act of 1972 puts all marine mammals in Schedule I of the Act, very little has been done in ways to mitigate mortality," he said.
The lack of such information has hampered efforts to evaluate the significance of ship strikes on whale population and to develop appropriate mitigation measures.
For some small whale populations or population segments, ship collisions can pose a substantial threat. Massive injuries on stranded ship-struck whales suggest large vessels are the principal source of severe injuries to whales, he said.
In many cases the cause of death of stranded animals was not properly examined and only a thorough necropsy by experts would precisely identify the causes, he said.
"This will facilitate a more reliable investigation into mortality and provide greater ability to evaluate and alleviate the impact of anthropogenic interactions," Kumar added.