Teeth taken from bottlenose whales change scientists’ views of life cycles

HALIFAX — The walnut-sized teeth taken from northern bottlenose whales slaughtered in the 1960s and 70s are proving to be storehouses of knowledge that raise awareness about the fragile future of the endangered species.

Dalhousie University researcher Laura Feyrer found she and other researchers could only observe the elusive mammals from rare sightings far off the coast of Nova Scotia, when their distinctive bulbous foreheads and beak-like mouths occasionally emerged from their deep dives.

It wasn’t sufficient to properly observe the whales’ behaviour, or to enhance the scant knowledge of their life patterns. But Feyrer and her collaborators came up with a technique to probe the life stories of the whales through a box of teeth taken from the animals by whalers off the coast of Labrador and Iceland, and retained by scientists at the Norwegian Institute of Marine Research for future study.

Using a small drill, the researchers selectively extracted samples of the tooth’s dentin that is deposited in annual growth layers, like tree rings, indicating what the animals were eating when they were alive.

The results published this week in the journal PLOS ONE showed the whales were nursing an average of three to four years before breaking away from their mothers.

That meant the whales’ ability to reproduce was much slower than previously thought, altering scientific understanding of their vulnerability to human impacts on their population.

“Previous studies suggested that northern bottlenose whales weaned when calves were one year old, which was based on what whalers found in the stomach of one northern bottlenose whale calf,” said Feyrer, a doctoral candidate at Dalhousie’s marine biology department.

“What I was able to see from their stable isotope profiles of their teeth was ... on average, they were still nursing at age three. So that’s an extra two years more than what was previously used to build reproduction models.”

The lead author said this helps assess the species’ ability to rebound from disease, or mass stranding events that can occur due to mid-frequency sonar from naval ships.

She said this could means that naval forces or seismic research vessels probing for oil and gas can use this added knowledge to assess their potential impact on the whales.