SEATTLE (AP) — Efforts to find a sick young orca from a critically endangered population of killer whales in the Pacific Northwest came up empty Thursday, and a scientist who tracks the animals declared her dead — though federal authorities said they'd keep looking.

The grim news means scientists believe just 74 whales remain in a group that has failed to reproduce successfully in the past three years. The orcas have struggled with pollution, boat noise and, most severely, a dearth of their preferred prey, chinook salmon, because of dams, habitat loss and overfishing.

"We're watching a populat...