A female adult Southern resident killer whale and her three-and-a-half-year-old calf are rapidly declining in health in what appears to be a troubling situation for the creatures.

Southern resident orcas are on the brink of extinction, while killer whales to the north are growing in numbers. The contrast exposes what’s killing Puget Sound’s orcas.

The biggest challenges for whales is the buildup of toxic chemicals in their bodies and the shrinking runs of Chinook salmon, their primary prey.

One whale-watched said it appeared to be a mother orca with a large dorsal fin and three to four young orcas.