Something disquieting happened at SeaWorld marine parks this year. Numbers attending the group’s popular US centres between January and March dropped, from 3.5 million in 2013 to 3.05 million this year, a decline of 13%. Nor is it hard to guess the cause, say wildlife campaigners. They see a clear link between the attendance slide and the release last year of the documentary Blackfish, which told the story of SeaWorld trainer Dawn Brancheau who was killed by Tilikum, a bull orca.