Monday, 3 November 2014

Blue Whales and Ships off Sri Lanka

Nearly a year ago we were off the southern tip of Sri Lanka to see Blue Whales. The chance of seeing the largest living animal that has ever lived was too good to be missed and the reliability of a sighting in the right season from the boats that are based at Mirissa was said to be extremely high. I am pleased to say that report was correct and if sea conditions are good then whales, as the photographs show, will be seen.

                                     AJP Photographs

Heading out from Mirissa to the sea of Dondra Head to the east where the continental shelf ends, one is not slow to realise that as well as spotting whales one is also spotting ships heading west—a steady stream of very large container ships. It also does not take long to realise that the Blue Whales are living in that shipping channel. The odd traumatic meeting of very large mammal and very large ship seemed inevitable. Indeed, I find there are reports of an increased number of blue whale strandings in recent years with some carcasses showing blunt force trauma. However, strandings in Sri Lanka would be an underestimate of any fatalities since during the north-east monsoon bodies would be carried away from that coast. The key question, of course, is whether fatalities or injuries from collisions with ships are having an effect on the size of the population and its ability to recover from exploitation in the past.

The whales really are in the shipping lanes                                                                                 AJP Photographs

Recently, I came across a new paper presented at the International Whaling Commission’s Annual Meeting of the Scientific Committee, held in May 2014, that set out to investigate this problem. The survey work was done between February and April 2014 (the report for the meeting must have been prepared with commendable despatch).  The abstract of the paper, Preliminary results of surveys to investigate overlap between shipping and Blue Whale distribution off southern Sri Lanka, says it all:

Surveys were conducted off the southern coast of Sri Lanka during February to April 2014 in order to investigate the distribution patterns of blue whales (Balaenoptera musculus) in relation to current shipping lanes and further offshore. There have been several reported ship strikes of blue whales in this area and the IWC Scientific Committee has recognised the potential for ship strikes to have population level impacts on blue whales in the northern Indian Ocean. A total of 1413km of visual survey effort was conducted on 16 survey days along north south transects between 5° 28’ N and 5° 53’ N. The highest densities of blue whales were observed in the current shipping lanes, peaking at an average of 0.12 individuals km-2 in the westbound shipping lane. These high densities of whales combined with one of the busiest shipping routes in the world suggest a severe risk of ship strikes. Previous data on blue whale distribution and coastal upwellings indicate consistent and predictable patterns of whale distribution, suggesting there is considerable potential for effective measures to keep ships and whales apart. 

This is one of the figures from the report showing the sightings along the transects as well as the shipping lanes (westbound to the north and eastbound to the south).

The next map shows a cut-down Figure 8 of the report. It plots the sightings of Blue Whales by the whale-watching boat Raja & The Whales (used for the survey; the Captain is a co-author) in 2013 and 2014. On that I have superimposed my camera GPS data for our sightings on two days in November 2013. No wonder we seemed close to the westbound shipping.

The question then arises of course as to whether the data showing a clear coincidence of whales, ships and whale-watching boats will have any effect in either moving the channels to the south or in introducing speed restrictions which appear to be effective in preventing collisions with whales. A related but pertinent question is will development of the new Chinese-funded port at Hambantota, along the coast to the east from Dondra Head, have any effect on the density and route of traffic through the water frequented by the whales?

AJP Photographs
The following is the video footage of Blue Whales, Orcas, Bryde's Whales and Spinner Dolphins I took on 25 and 26 November 2013. It can also be seen directly on YouTube here and here.