Popular Science, August 2011
The first isolated instances of conching were recorded in 2007 and 2009 among a small group of Shark Bay’s dolphins. But other dolphins seem to be observing that behavior and learning the method for themselves–in the last four months alone, researchers have documented the behavior six or seven times–marking a very rapid horizontal spread of behavior.
https://www.popsci.com/science/article/2011-08/clever-new-fishing-method-conching-catching-australias-bottlenose-dolphins