Answer to mystery photo

UPDATE on the "what is this" photo below. Marie was the closest. This contraption IS indeed a large sling shot... for fishing! The river shown is the Columbia River Gorge. After my family stopped check out the Bonneville dam there was a pull out for people to fish. There was a man there with this crazy sling shot and a few other contraptions. He gave us a demonstration. He loads his weight and bait and shoots it out across the river! The white barrel relieves the tension (not sure how) off the fishing pole, otherwise it would snap. Amazing! It was really something to watch. Man was a big kid at heart :)