Keeping killer whales in captivity in marine parks to perform for human entertainment has been at the centre of a growing controversy for a long time.
Critics say the tourist attractions deprive these intelligent animals of normal behaviours such as hunting in groups and forming social bonds.
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Now California has become the first state to ban the practice.
A new measure would prohibit such performances and would also ban breeding the whales in captivity.
The move follows a public outcry sparked by the 2013 film Blackfish which cast a spotlight on the cruelty of keeping the orcas in captivity.
SeaWorld, which has parks in California, Florida and Texas, had already been moving in that direction.
It announced in March that it would no longer breed orcas and would stop making them do tricks.
The new California law makes sure this will actually happen.