SEATTLE -- When Dr. Sam Wasser and his University of Washington team want to find orca poop, they follow the nose of a black lab named Tucker.

Tucker can smell it from miles away and, through body language in the bow of a boat, guide them to the floating orca waste. Once they have that, the team follows the hormones to some surprising conclusions.

Southern resident orcas almost exclusively eat Chinook salmon. Wasser said stress hormones measured in the poop at times when there are plenty of Chinook in the San Juans show the orcas are calm.

When Chinook numbers drop, the orcas' stress goes up, and, says Wasser, it goes up much higher than when the orcas are surrounded by whale watching boats.

He cautions the boats can add to the stress when the orca are already hungry, but in his words, It's definitely the fish that are driving the bus when it comes to stressed-out salmon.

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