Awareness that Sri Lanka is the top spot in the world for seeing and photographing Blue Whales began in May 2008. This hinged on the Anderson hypothesis that the Blue Whales undertook an East-West migration between the Arabian Sea off the Horn of Africa and the Bay of Bengal. I have likened it to a U –shaped migration. However, on a global scale it can be viewed as a horizontal movement or if at all as one with a very shallow U shape, as the whales curve around the South of Sri Lanka.
The migration is driven by the seasonal presence of food: the krill upon which the Blue Whales feed, is typically in the top 60 metres of water, but they could be feeding down to 300-400m. The strong winds of the south-west monsoon physically displace water away from the African coast. Water must well up from below to replace the water which has been pushed away. The up-welling created, brings up nutrients which lead to a blooming of phytoplankton which are in turn fed on by zooplankton such as krill and creates a food chain for other marine animals. The Blue Whales return to feed on this seasonal blooming of krill.
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Similarly, their journey to the Bay of Bengal would have been triggered by a seasonal blooming of krill which would have been triggered by upwellings created by the north-east monsoon. In other words, the Blue Whales go to the areas where the seasonally changing monsoon currents produce seasonally changing plankton bloom areas where the south-west or north-east monsoon has abated from.
Blue whales seem to be found most commonly along the continental slope, where the relatively shallow inshore waters of the continental shelf drop away steeply to the ocean depths. It is along this slope that local upwellings may occur and where plankton are often concentrated.
Where the continental shelf comes close to shore, it may also allow the whales to come closer to the nutrient flow from a land mass which will create a food chain close to shore. In Western Scotland, currents creating nutrient flows and food chains resulted in massive fish stocks close to shore, which led to a large fishing industry. We have a similar situation off the Kalpitiya Peninsula where it seems currents, nutrient flows and the proximity of the continental shelf has created a large Yellow-fin Tuna fishery close to shore.
Where there are fish, there is a food chain. We can therefore also find whales, whether they are baleen whales or toothed whales, feeding in their niche in the food chain, close to shore in Sri Lanka off Mirissa, the Kalpitiya Peninsula and Trincomalee. It is also my personal belief that deep water offers whales a higher degree of manoeuverability when facing predators. So the plankton rich deep waters close to the Sri Lankan shore provide both food and safety.
Which theory is correct: Resident or Migrant or both? The Anderson hypothesis which I publicized of an E-W migration (shallow U-shape, for graphical dramatization by me) seemed to run contrary to the alternative belief that the Blue Whales were present all year round. Neither Dr. Anderson nor I challenge the idea that some Blue Whales are present in Sri Lankan waters throughout the year. Data going back several decades suggest that this is so. It is also possible that such resident whales change (or migrate locally) from one coast line to another to be on the lee-ward side of any prevailing monsoon. However, where Dr. Anderson and I take a strong position is that the large majority of whales which are seen during the period November/December to April participate in a migration between the Arabian Sea and the Bay of Bengal as proposed by Dr. Anderson. I would emphasize once again this does not preclude resident Blue Whales also being seen by the whale watching boats.
It appears we are looking at two strategies used by the Blue Whales found around Sri Lanka: a smaller resident group and a larger seasonal influx of migratory Blue Whales. The fact that we have been observing directional movements eastwards around November/December to January and westwards around March to April seems to support the theory of the migrant Blue Whales. It also fits in with the seasonality of Blue Whale sightings and strandings in the Maldives. Also, if there was no migratory influx, then on calm days in the ‘off-season’ we should see Blue Whales with the same abundance/frequency as during the December to April season. But this is not the case.
However, there is some confusion that the theories “migrant versus resident” are mutually exclusive. Furthermore, some prefer to believe that almost all of the Blue Whales are present throughout the year. So much so that we were asked quite innocently whether an observation of 25 individual Blue Whales travelling together on November 5, 2010 may point to the presence of Blue Whales being sedentary around Sri Lanka. On the contrary, I think this is one of the most significant observations to support the Anderson hypothesis. I received emails on this sighting from several people. Realizing how significant this observation was, I asked naturalist Anoma Alagiyawadu who was on the boat, for more information. In particular I enquired if any directional movement had been observed.
He has very sharply observed that the whales were single (these would be adult males) or in pairs (mother and calf), although moving together. Whether it is millions of Wildebeest bunched up on the Mara migration or 300 elephants on a one kilometre quadrat during ‘The Gathering’ at Minneriya, animals still keep to their basic social units. In the case of Blue Whales it would be a lone male or a mother with a calf. It should be borne in mind that Blue Whales can communicate across hundreds or even over a thousand kilometres using infra sounds. Therefore, Blue Whales a few kilometres apart, may in their spatial terms, be as close as humans are when walking together a few feet apart. As a result, I had thought we may not see a physically close together concentration of Blue Whales as was observed on November 5. I did on one occasion see at least 8 simultaneous Blue Whale spouts in April 2008. Others on the boat guessed there could be anything from 15 to 20 Blue Whales. I could only be sure that there were at least 8, but I knew the number was probably much more. I suspect that was a group on the return migration.
Anoma Alagiyawadu was on his 234th whale watching trip, more than any other person in Sri Lanka except the (Mirissa Water Sports) MWS crew. He is a trained naturalist observer. His claim of 25 individual Blue Whales travelling together is a safe observation. He is a trained observer able to distinguish ‘sightings’ from ‘individuals’. But be aware that many claims of 20 plus Blue Whale sightings in a single session usually relate to multiple sightings of 4-5 Blue Whales. Alagiyawadu also commented that there were almost certainly many more travelling together on that day.
Anoma Alagiyawadu’s remarkable sailing began as usual at 7.30 a.m. from the fishery harbour at Mirissa in the South of Sri Lanka, close to Dondra Head, the island’s southern-most point. At 10.05 a.m., they found a Bryde’s Whale around 12.42 nautical miles from Mirissa. He writes, “When we were coming back to Mirissa, it was very windy. At 10.40 a.m. at a distance we spotted a few blows. We thought they were Sperm Whales”. Alagiyawadu says they thought they were Sperm Whales at a distance because the strong wind was keeping the blows short and probably slanted like that of a Sperm Whale and not tall and straight as with a Blue Whale. I also suspect because there appeared to be at least a few clustered together, sub-consciously, Sperm Whales rather than the Blue Whales seemed the right conclusion.
He continues to say, “Ten minutes later we recognized they were Blue Whales. We could not believe we were seeing such a large group of Blue Whales. They were travelling West to East. The current in the water was also running West to East. They were moving a little bit fast, doing shallow dives, and looked like they were travelling on the surface. We were 8.86 nautical miles from Mirissa with the water temperature at 83.20F. All the whales were travelling close to each other, but either individually or in pairs. I counted 25 around me, but definitely there were more, I am sure of that.”
Wow! You can imagine how I felt reading this. The timing of the observation does raise questions. Were they unusually early this year and if so why? Or is it that the migration starts earlier than the December-January period which I had publicized earlier in several previous articles? In November 2008, between the 7th and 30th, Blue Whales sightings were reported on whale watching sailings. On November 30, 2008, Alagiyawadu reported what were potentially 9 different Blue Whales at four observation points. Dr. Anderson commented in the Sri Lanka Wildife eNewsletter (September – November 2008) that there was a time when he thought that the whales began to move past Sri Lanka in November but the data from the Maldives had not supported it. It is possible that the migrant whales may be arriving earlier than the December-January period. Perhaps we have been missing the massed arrival in previous years because the seas have been rough or there has not been much appetite to go out. This is possible but more data is needed. Alagiyawadu, myself and others have sailed in October and November, but more data is required than the few sailings so far to be able to draw conclusions. Sightings and nil sightings are equally important and the data for the over 200 sailings are available on www.jetwingeco.com.
I suspect that as with some species of birds, the photographic records of whales, will show that Sri Lanka has both resident and migratory individuals. I also suspect that in the years to come, a large body of the data will come from pictures posted on to public sites on the internet such as Flickr and Facebook. The automatic GPS encoding on future compact cameras will give rise to a wealth of data to individually identify Blue Whales and their movements. A Facebook or Flickr account acting as a portal for uploading images taken on commercial whale watching sailings will provide a wealth of data to tracking the movement of Blue Whales. Interested land lubbers could become amateur marine biologists.
Next week: Is whale watching better at Mirissa or Trincomalee?
Wildlife expert Gehan de Silva Wijeyeratne can be found on Facebook and www.flickr.com. |
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