June 7, 2010

Commercial Whaling May Break Up Social Groups

A new finding raises the possibility that commercial whaling may have taken a role breaking apart social groups of whales.

Dr. Christian Ramp and colleagues of the Mingan Island Cetacean Study group based in St. Lambert, Canada have been studying whales since 1997 in the Gulf of St. Lawrence.

The scientists are recording the movements of baleen whales including blue, fin, minke and humpback whales, adding to a set of data that stretch back 30 years.

The team found that individual female humpbacks reunite each summer to feed and swim alongside one another in the Gulf of Lawrence, off Canada.

Baleen whales, the largest of all whales, possess huge baleen plates in their mouths, which they use to filter out small prey such as krill and plankton from the water.

The researchers can spot which individual whales appear from one year to the next by using photographic identification techniques.

They found that the same humpback whales reunite each year.

Individual humpbacks somehow find each other again in the open ocean each summer after spending the rest of the year apart migrating and breeding.

The longest recorded friendships lasted six years and always occurred between similar-aged females, and never between females and males.

"I was very surprised by the prolonged duration," Dr Ramp told the BBC.

"I was expecting stable associations within one season, not beyond. I was particularly surprised by the fact that only females form these bonds, especially females of similar age."

The researchers have been puzzled by the discovery.

"In toothed whales, you find strong bonds in killer whales, between entire families, and sperm whales between females and juveniles. They basically stay together all their life. There are also strong associations in bottlenose dolphins," Ramp told BBC.

But "as far as we know, baleen whales are regarded as less social than toothed whales."

In Alaska, there is some evidence that humpbacks form stable groups to feed on herring, and female right whales are thought to be more gregarious than males.

However, baleen whales have not been known to reestablish bonds between individuals from one year to the next, until now.

Forming these bonds clearly benefited the female humpbacks, as those that had the most stable and long-lasting associations gave birth to the most calves.

Ramp and his colleagues suspect that the whales form bonds to improve their feeding efficiency every year.

"Staying together for a prolonged period of time requires a constant effort. That means that they feed together, but likely also rest together. So an individual is adapting its behavior to another one."
It is also a mystery of how the whales find each other every summer.

"It's an excellent question and I would like to know the answer," says Ramp.

"Where do they meet, and how do they recognize each other?"

He believes the whales use sound to find and recognize one another.

Studies on blue and fin whales suggest that these species do not form such friendships.

However, the discovery that humpbacks do provides further implications.

Ramp speculates that humpbacks associating with one another may have made it easier for them to be caught in the past by commercial whalers, although there is no evidence yet to support this

However, if this were the case, it would mean that whaling may have removed social groups of humpbacks, and their preference to form friendships with other whales.

"Maybe the social traits are re-evolving due to rebounding populations, or they are completely different to the ones before, due to changes in the environment."


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