Image copyright AP Image caption The new tanks will be twice the size as the current ones, which animal rights groups say are too small

US marine theme park SeaWorld has announced it is to build a bigger tank for its killer whales, amid criticism of its treatment of the animals.

But the Florida company said that the plans were not in response to last year's documentary film "Blackfish".

The film suggested that captivity and SeaWorld's treatment provoked violent behaviour in the killer whales.

The high profile death of a trainer in front of a live audience in 2010 sparked worldwide outrage.

SeaWorld CEO Jim Atchinson said in a statement on Friday that the new tank, to be completed by 2018, would "transform how visitors experience killer whales".

Image copyright AP Image caption The 2013 film 'Blackfish' argued that whales in captivity become traumatised and turn violent

"Our guests will be able to walk alongside the whales as if they were at the shore, watch them interact at the depths found in the ocean, or a bird's eye view from above."

The new tank will be almost twice the size of its current orca tank, with 10 million gallons of water and a new depth of 50 feet (15m), and will include larger viewing points for visitors.

But Peta (People for the Ethical Treatment of Animals) criticised the plans, calling them a "desperate move".

"A bigger prison is still a prison," it said in a statement.

The animal rights group warned that nothing but moving the orcas to seaside sanctuaries to feel and experience the ocean again and hear their families would "save the company", which has seen its profits slump in the past year since it went public.

Image copyright AP Image caption Dawn Brancheau was killed by the whale 'Tilikum', whilst performing in a show at SeaWorld in 2010

Peta filed a lawsuit against SeaWorld in 2012 and named five killer whales as plaintiffs, arguing that they deserved the same constitutional protection from slavery as humans.

Dawn Brancheau, 40, who had more than 16 years of experience in killer whale shows was killed whilst performing with "Tilikum".

She died from drowning and traumatic injuries after the whale bit and dragged her underwater in front of an audience.