Marine Biologist John Calambokidis showed a series of slides and some video and one listed what they found including "50 gallons of undigested contents, mostly algae but 3.2 lbs were "human debris, including plastic bag material, fabrics (including a leg of sweatpants), fishing line, golf ball, duct tape and a juice pouch.
15 oz of the total debris were plastic bag pieces alone." He said this indicated that the whale had clearly been feeding in the waters in and near Puget Sound to have picked up this much debris.
Gray whales are filter feeders, scooping material from the sea floor that contains their prey, most commonly Krill, a shrimp-like marine invertebrate animal or in our waters near Camano Island as he pointed out, a species known as Ghost Shrimp. Whales have a structure called baleen "a dense seive like matt that will filter out anything passing through it," he said. They force their tongues against the roof of their mouths forcing the water out and swallowing what remains.