The Cove is a 2009 documentary film documenting the annual killing of more than 2,500 dolphins in a cove at Taiji, Wakayama in Japan. The film was directed by former National Geographic photographer Louis Psihoyos, and was filmed secretly during 2007 using underwater microphones and high-definition cameras disguised as rocks.
Considering they can't wield a knife or cleaver, dolphins make impressive butchers. Researchers in Australia recently observed a bottlenose performing a precise series of manoeuvres to kill, gut and bone a cuttlefish. The six-step procedure gets rid of the invertebrate's unappetising ink and hard-to-swallow cuttlebone.
When the bubbles [formed by cavitation] collapse, they produce a shockwave, which eats away the metal in propellers. To dolphins, it is painful. According to the researchers' calculations, within the top few metres of the water column, this happens when the dolphins reach 10 to 15 metres per second (36 to 54 kilometres per hour).
Tuna don't have this pain problem; their tails don't have nerve endings.