Sameera Madusanka Randage’s research while affiliated with University of Ruhuna and other places

Surveys were conducted off the southern coast of Sri Lanka in 2014 and 2015 to investigate the distribution patterns of blue whales (Balaenoptera musculus spp.) 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 3268km of visual survey effort was conducted on 35 survey days along north-south transects between 5° 28’ N and 5° 53’ N. These data were used to model patterns of whale density. The highest densities of blue whales were observed in the current shipping lanes, peaking at an average of 0.1 individuals km-2 along the westbound shipping lane. Automatic Identification System transmissions received by satellite were used to estimate shipping density. Between 80o 30’E and 81oE, the peak mean shipping density in the westbound lane of the Traffic Separation Scheme was 1090 km-1year-1 and in the eastbound lane 810 km-1year-1. 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. For example, data from this study would suggest risk could be reduced by 95% if shipping were to transit 15 nm further south than currently.

A population of blue whales is resident off the southern coast of Sri Lanka and has been observed year-round by the crew of a whalewatching vessel, Raja & the Whales, a few miles south of Mirissa Harbour. Over the course of three years (1 December 2009 to 30 November 2012), a total of 485 blue whale sightings were reported with an average of 4.56 individuals observed per sighting. This number does not represent the total number of individuals seen because repeat sightings were highly probable. Calves were observed during the northeast monsoon. Sightings were confined to an area of about 200 n.miles that is bisected by a heavily trafficked shipping lane. Much of this area is characterised by submarine canyons and sloping bathymetry, which contributes to monsoonal seasons of high productivity and upwelling suitable for feeding whales. While the numbers of injuries and fatalities due to ship strikes are not known, four dead blue whales were observed along the southern coast over the course of five months (1 January to 31 May 2014). It is of great urgency to understand the identity and size of this population, reduce ship strikes and address all issues threatening this population in order to arrive at possible mitigation measures for its protection.