To sum up, Sri Lanka’s location, marine topography and double-monsoon weather system make it an unusually hospitable location for marine mammals of many species. Seven natural factors combine to produce an island ecology offering a wide variety of marine habitats, making Sri Lanka one of the best places in the world to see whales and dolphins as well as other marine mammal species:
A location at the southernmost extremity of a tapering continental landmass, with expansive, unbroken stretches of deep ocean separating the island from other landmasses to the west, south and east, renders it a transit point for migrating and itinerant cetaceans.
A ratio of inland surface-water-to-land area of 3ha/km², one of the world’s highest results in an unusually large annual surface water discharge to the sea, supplying ample resources for primary production. The marine food chain in Sri Lanka’s coastal and oceanic waters thus rests on an unusually broad and rich base.
The oceanographic impacts of the southwest monsoon are among the greatest produced by any terrestrial weather system, and its (largely beneficial) influence on marine life is enormous. Monsoon discharges from the Western Ghats in southern India carry rich source materials for food production into waters off the northern and western coasts of Sri Lanka, while the south and south-eastern coastal waters benefit similarly due to discharges from the Wet Zone of the island itself.
The mass transport of nutrient-rich water from the Bay of Bengal into Sri Lankan waters during the northeast monsoon, creates a second seasonal source of material for primary production, ensuring that food is abundant in these waters throughout the year. A narrow continental shelf, averaging 22km (12nm) in width and often pinching in close to the shore, renders the island’s plankton-rich coastal waters easily accessible to great whales and other deepwater species and makes Sri Lanka one of the best places in the world to observe cetaceans close to shore.
An unusually high prevalence of submarine canyons along the island’s coast provides abundant food resources by creating movements of pelagic water that contribute to the process of ‘nutrient cycling’.
The warm tropical seas around Sri Lanka, along with monsoon and tidal currents, cause vertical mixing of water layers in the multitude of channels and estuaries that line the island’s coasts – another effect believed to help create nutrient-rich conditions hospitable to marine life
Text by Howard Martenstyn, Out of the Blue