Strike out for blue whales

Fifteen miles off the southern coast of Sri Lanka lies one of the world’s busiest shipping lanes. Ship strikes are a leading cause of whale deaths around the world. Any size or type of vessel may be involved in a collision, but risk of injury or fatality appears to correlate with vessel speed and mass.

Fifteen miles off the southern coast of Sri Lanka lies one of the world’s busiest shipping lanes. These waters are also home to the blue whale, indeed some commentators are starting to venture the opinion that Sri Lanka may be the best place in the world to view this gentle giant, the largest creature ever to inhabit our planet. Decimated by whaling last century, probably only 10,000 - 25,000 blue whales remain worldwide and the species is classified as endangered.

Blue whales congregate to feed off Mirissa, close to the Traffic Separation Scheme (TSS) south of Dondra Head which sees numerous ships transiting the area at high speed, day and night.  Sadly, ships and whales do not make good bedfellows: last year, five blue whales and two sperm whales washed ashore dead with massive propeller cuts and this spring, a further two blue whales were fatally struck by ships within a ten-day period. The true death toll is likely to be much higher and some experts suggest that only 10% of carcasses are ever retrieved. Non-fatal strikes are also a concern and strike injuries can result in the death of the whale even some years after the actual collision.

Ship strikes are a leading cause of whale deaths around the world. Any size or type of vessel may be involved in a collision, but risk of injury or fatality appears to correlate with vessel speed and mass.

So what can be done? Tools such as propeller guards, posting look-outs, use of acoustic detection systems and relocating a TSS have all been promising, but are not without their drawbacks. At the current time, research [1] suggests that the best method of reducing severe injury or death to large whales is to slow vessels in the vicinity of whales to 10 knots or less.

WDC, therefore, urges all efforts to increase vigilance of bridge crews and voluntarily reduce speed when transitting the TSS south of Dondra Head. The message is simple: slow down and save whales!

[1] Vessel collisions with whales: The probability of lethal injury based on vessel speed." Angelina SM Vanderlaan, A.S.M. and C. T. Taggart. (2007) MARINE MAMMAL SCIENCE, 23(1): 144–156.