Jan 15 2009 Whales overwintering in Bermuda Print
Written by Andrew Stevenson   

Today, at 3p.m. on January 15th, while looking casually over Grape Bay from our cottage, I spotted three humpback whales spouting about 300 yards off the breakers of Grape Bay Beach. They spouted once again and then disappeared. I picked my daughter up from school and drove to Coral Beach and searched unsuccessfully for them there. Then I drove to Williams Estate (Pokiok Estate) and after 15 minutes, at  4.15 p.m. saw a whale breach far out on the horizon, some miles away. A few minutes later two whales surfaced about fifty yards from the breakers almost on the shoreline. The second whale did a small tail lob and then they were gone. With the extensive views afforded from that vantage point and given the absolute calm conditions, I knew I would see them when they resurfaced. It was almost half an hour when the two whales surfaced again, only two hundred yards from where I had observed them before. They dived and disappeared. I waited 20 minutes, didn't see them resurface, and left around 5.20 p.m.

 

What were these whales doing? The water is shallow, some 70 feet deep there. Were they singing? Resting? Feeding? The previous two days we had strong gale force winds. Was there an upwelling close to shore with krill, pilchards? Looking at the surface of the water, there did seem to up an upwelling line running east-west.

 

I have received emails and spoken to fishermen who tell me they have seen whales out at Challenger (where there is a lot of baitfish and tuna), and on Sally Tuckers, on to the south-east along the South Shore over the Christmas period. It is far too early for whales to be migrating north. If these were whales migrating, they would be going south, but the humpbacks don't seem to bother coming close to our shores when they migrate south (when their bellies are full and there's no incentive for them to pass close by). I would guess that these whales are overwintering on the mid-ocean seamounts (of which Bermuda is only one of many, but the only one that rises above the surface of the water, providing us with an ideal platform to study the humpbacks).

 

The most extensive study of humpbacks took place here in the North Atlantic Ocean some years back. This three-year study revealed that while the male to female ratio of humpbacks is one-to-one in their northern feeding grounds, it is four-to-one in the southern breeding grounds in the Caribbean. Where are the females during the winter breeding season?

 

They must be on these mid-ocean seamounts. My guess is, if a female humpback whale is too young or too old to breed, there is no reason for them to go all the way down to the Caribbean where they have no access to food and are harassed by overzealous testosterone-laden males. I would surmise the young male humpbacks who are too small to compete with a larger male for a female's attention are still going to go down to the party down south in the hope that they might get lucky. Meanwhile the females hang around these mid-ocean seamounts and opportunistically feed off the krill and zooplankton and pilchards that rise with the upwelling currents that can occur on these seamounts.

 

Dr Hal Whitehead from the University of Dalhousie did a transect from Halifax to the Caribbean last February to find sperm whales. Every half hour he dropped a hydrophone overboard and on 45% of those occasions, some hundreds of miles to the east of Bermuda, he heard humpbacks singing. If if the humpbacks were singing, this means there were males around (unless the females sing, but no whale expert seems to think that is the case). Perhaps there are enough females overwintering on the mid-ocean seamounts that some of the males are remaining there too. This is probably an indication of a healthy humpback whale population because going through Bermuda's archives I have come across several references to humpbacks being in Bermuda waters during the winter, although the greater numbers were in the March to June period.

 

If the humpbacks are singing on the mid-ocean seamounts, wouldn't the orcas hear them and come down to attack them? Not if they are not young calves, and if they are grouped in larger social units.

 

I have just returned from Australia and New Zealand where I had useful discussions with Dr Rebecca Dunlop at the Cetacean Ecology and Acoustics Laboratory School of Veterinary Sciences at the University of Queensland, and Dr Greg Stone of the New England Aquarium. Both thought that my observations on humpback whale singing in Bermuda to be entirely plausible. Why do we hear humpbacks singing 24/7 here in Bermuda as late as May, long after the breeding season is over? My conclusion, based on observations, is that large males are aggregating whales into larger social units to run the gauntlet of orcas further to the north.

 

The three-year study of the North Atlantic humpback whales referred to above revealed that there was a general melee of whales in the breeding grounds down in the Caribbean. In other words there was no rhyme or reason for a whale to be in a certain location at any point in time. It's a big party scene with males chasing females trying to mate. However, the humpbacks do maintain site fidelity up north in their breeding grounds as any whale watch tour operator knows (typically they will recognise the same whales return year after year). So where do the whales gather into their loose social units that they form up north? Could it be the mid-ocean seamounts?

 

There is an incentive for the whales to gather into large social units mid-ocean before heading north. A quarter to a third of the North Atlantic humpback whales have bite marks on their flukes, pectoral or dorsal fins incurred when they were calves. By gathering into large social units of ten or more whales (see some of my underwater video footage on youtube) they are able to run the gauntlet of orcas up north. Interesting stuff and I hope this season to observe the same kind of activity. There aren't enough whales to observe around Bermuda to make this quantifiable data and therefore good science, but the observations if repeated, do provide an insight into the whales' lives and lead me to conclude that their social ties and responsibilities to each other are far stronger than we think.