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Environment | Flora and Fauna

Puget Sound Orcas' Latest Problem: Inbreeding

An Orca off Puget Sound's San Juan Islands

An Orca off Puget Sound’s San Juan Islands

Ashley Ahearn

Add this to the list of problems for Puget Sound’s orcas: instead of mating with outsider whales, they’re hooking up within their own pods.

The result? So much inbreeding that their genetic diversity could be diminishing, further jeopardizing their ability to survive.

That’s one of the conclusions of a new report in the Journal of Heredity. The National Oceanic and Atmospheric Administration weighed in on the report Thursday.

“One implication of this inbreeding behavior is a significant reduction in the genetic diversity of what is already a perilously small population of animals,” the agency said in a statement.

Orcas in Puget Sound were placed on the federal endangered species list in 2005. That population numbers 85 animals. Researchers have been looking for clues to understand why the three pods in this group of whales have not grown in population despite recovery efforts and protection. Officials say stress in the heavily boat-trafficked waters and toxins are contributing to their challenges. Now, a lack of genetic diversity is being added to the list of problems.

The new research analyzed 78 Puget Sound orcas for what NOAA calls “DNA fingerprints,” and inferred the paternity for 15 mother-calf pairs. The study found no evidence that these whales mate outside their population, but clear evidence that they do sometimes mate with members of their own pod.

These whales are known to visit the waters of British Columbia and have been found as far south as Monterey Bay, Calif. A separate group of orcas also visit the waters of Washington state as part of a range that extends north to Alaska. But, according to the new report, the two populations are distinct and do not socialize. Inter-pod mating has never been detected between these northern and southern groups.

Michael Ford, lead author of the study, said he and his colleagues are particularly worried about the lack of genetic diversity.

It puts the group of whales “at risk of genetically deteriorating further from a potential increase in inbreeding or harmful mutations,” said Ford, a scientist with NOAA’s Northwest Fisheries Science Center in Seattle.

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