According to news reports, two dolphins collided causing one to die from a fractured skull. Because there was no witness to the incident, the exact nature of the accident is uncertain.
While zoo officials have described the death as a "freak incident" dolphin experts point out the dangers of keeping dolphins in small, unnatural environments, that may make such accidents more likely. Other recent incidents include dolphins jumping out of tanks.
The criticism comes at a time when there is close scrutiny of the industry resulting from the recent deaths of two orca trainers at Loro Parque in the Canary Islands and at SeaWorld in Florida, the subject of a hearing next week involving SeaWorld and the US government's Occupational Health and Safety Administration.
For the full story: http://www.wired.com/wiredscience/2011/09/nea-dolphin-death/