Migration Through Sri Lankan Water

Wednesday, November 11th, 2020 | Blog

Experts disagree on where and by what routes whales arrive and depart the water around Sri Lanka. Reliable migration data on cetaceans in the Indian Ocean is thin Many hypotheses have been and continue to be proposed in various publications The information given below is based on the latest studies and data; however, it must be stressed that none of the possible cetacean migrations hypothesized or discussed herein can be confirmed without further information becoming available.

The first question concerns what types of habitat the waters off Sri Lanka offer migrating cetaceans. Should our waters be classified as breeding or grounds? Observations and records to date support both hypotheses, but the weight of evidence leans more heavily towards Sri Lankan waters being used as a feeding area. The available data, however, is very species-dependent. The topic is discussed in detail in a separate volume (Sri Lanka Marine Mammal Research and Conservation 1560-2018: Volume I, Martenstyn 2018), in which information is given for each species and the various possibilities are discussed.

Cetaceans may enter or depart Sri Lankan waters from known habitats such as the northern Arabian Sea (Gulf of Oman), the Laccadive Sea around the Chagos-Laccadive Ridge, off the coast of East Africa (Somalia), the Bay of Bengal around the Ninety East Ridge, off western Australia and even the Antarctic, which is a recognized summer feeding zone for migratory cetaceans such as blue, fin, sei, humpback and e whales.

It appears is the majority of blue whales in Sri Lankan waters leave the eastern coasts of the island towards the end of April and the southern coasts in May. Acoustic recordings indicate that three distinct subpopulations of blue whales may occur in Sri Lankan waters. Do these data suggest that most blue whales seen in these waters from October to April are pygmy blue whales? Humpbacks have been recorded migrating over distances of more than 8,000km (4,300nm), so their migratory destinations could be as far away as the Southern Ocean – or as near as the Gulf of Oman, where a population of humpbacks is thought to be resident.
Sperm whales appear in large numbers in the Gulf of Mannar to partake of the annual squid feast during the first inter monsoonal period (March-April). They seem to arrive from the south. Between the end of the same period and mid-May, other sperm whales vanish from their usual haunts off the east coast of Sri Lanka, migrating to a destination as yet undiscovered. Whether there is any connection between these mysterious movements is, for the moment, unknown.

The answers to these, and many other questions on the migrations and movements of cetaceans, must await the results of studies yet to be conducted. In the meantime, the comings and goings of these awe-inspiring mammals remain an intriguing mystery.

Text by Howard Martenstyn, Out of the Blue