Catching the culprits is hard, officers say: It often requires night patrols and undercover stings.

"Sturgeon poaching is not something that's done in the middle of the day when it's sunny," says Washington Department of Fish and Wildlife Sgt. Jeff Wickersham. "It's very hard to detect."

Detecting poachers has become a bigger part of wildlife police work in Washington and Oregon. Global sturgeon populations are collapsing — most notably in Russia, where caviar is known as black gold. That's fueling a market for illegal caviar and driving poachers to the Columbia River.