Pacific Whale Watch Association

Wed, 12/03/2008 - 17:22
Robert Barron, The Daily News
Published: Tuesday, December 02, 2008

Scientists monitor population but aren't too alarmed by deaths

The loss of seven killer whales in the southern Strait of Georgia sounds worse than it is, says Dr. John Ford.

Ford, a marine biologist at Nanaimo's Pacific Biological Station, said it's "certainly not a good thing" that the salmon-eating population of the area has seen a decline in its numbers from 90 to 83, but the deaths were spread over a two-year time period and most were from natural causes. "If all the deaths occurred in just one year, such high mortality would be cause for concern in a population of whales that has such low numbers," Ford said on Monday.

"Two of the seven were old females past their average life expectancy (Lummi, estimated to be 98, and Ankh, 58) and two others were newborn calves which typically have about a 45% chance of dying in their first year."

However, Ford said two deaths (Splash, 33, and Blossom, 36) are a concern because they were females in their reproductive prime. The seventh whale, six-year-old Aurora, is missing and considered dead.

"A population with such low numbers need as many females breeders as they can get," he said. "The numbers of chinook salmon (the main food for resident whales) are down in the strait this year and there may be a connection with these deaths."

Ford said resident killer whale populations in the Strait of Georgia have decreased in the past when chinook salmon were scarce, but rebounded when chinook became more abundant.

He said it's estimated that chinook populations in the strait are expected to "increase slightly" next year and marine biologists will be closely monitoring the southern resident killer whale population to see if their numbers dwindle any further.

"The northern resident killer whales in the strait are doing well, with about 250 whales, but they are still considered threatened so we're keeping a close eye on them as well," Ford said.

Ford said the population of meat-eating transient killer whales, which have a range around Vancouver Island and as far north as Alaska, is also strong at more than 250.

"They've been coming into the Strait of Georgia more and more over the past two decades as the population of harbour seals in the strait has increased tenfold (to about 39,000) since the bounty on seals was discontinued in the 1960s," he said.

"They are especially numerous in August and September which is pupping season for the seals."