Lolita, an orca held captive for more than half a century at the Miami Seaquarium, has died at the estimated age of 57 from suspected kidney disease.

Also known as Tokitae or Toki, she was believed to have been the world’s second-oldest killer whale.

Her death on Friday came as her caregivers were making preparations for her to return to the ocean in the near future.

The Seaquarium posted a statement saying the whale had “started exhibiting serious signs of discomfort” over the last two days, for which they said she had been treated “immediately and aggressively”.

They went on: “Despite receiving the best possible medical care, she passed away Friday afternoon from what is believed to be a renal condition.”

Staff went on to call her “an inspiration” and a “beautiful spirit,” highlighting the Lummi Nation (a Native American tribe based in Washington state) who they said “considered her family”.

The theme park also shared a short video on social media showing her performing tricks in her pool and interacting with her keepers.

A life in captivity

Lolita had spent decades performing for Miami crowds after being captured in the summer of 1970, when she was around four years old, during a period of deadly orca roundups.

An orca believed to be her mother, Ocean Sun, who is now in her 90s, continues to swim free with other members of their clan in the waters between Washington state and Canada.

Animal rights activists have since spent years fighting to have Lolita – who weighs 5,000lbs (2,267kg) – freed from captivity, where she lived in a tank that was 80ft by 35ft (24 metres by 11 metres) and 20ft (6 metres) deep.

She retired from performing last spring as a condition of the park’s new exhibitor’s licence with the US Department of Agriculture and had not been publicly displayed since.

Earlier this year the park’s relatively new owner, The Dolphin Company, and the non-profit Friends of Toki announced a plan to move her to a natural sea pen in the Pacific Northwest, with the financial backing of Indianapolis Colts owner Jim Irsay.

‘I am heartbroken’

Responding to her death, Mr Irsay said: “I am heartbroken that Toki has left us.

“Her story captured my heart, just as it did millions of others. I was honoured to be part of the team working to return her to her indigenous home, and I take solace in knowing that we significantly improved her living conditions this past year.

“Her spirit and grace have touched so many. Rest in peace, dear Toki.”

President of The Dolphin Company, Eduardo Albor, wrote on social media: “Not a single effort we made to give Lolita an opportunity was a waste of time & money. My heart is truly broken.

“Lolita captured me since 1st day. Love at first sight. Thank you for making [me] believe in what we do. The care team led by Mike Partica and Dr. Reiderson are true heroes.”

Tony Hillaire, the chairman of the Lummi Nation – who have spent years working to secure Toki’s release and to return to her home waters – said: “The Lummi Nation is saddened by the news that our beloved Orca relative has passed away at the estimated age of 57 years old.

“Our hearts are with all those impacted by this news; our hearts are with her family.

“We stand in solidarity with our Lummi members who poured their hearts and souls into bringing Sk’aliCh’elh-tenaut [Toki’s name in the Lummi language] home.”

In recent months, new upgrades had been installed to better filter the orca’s pool and regulate her water temperature.

Despite Lolita’s freedom being in sight, there would have still been hurdles to overcome, with federal and state regulators still needing to approve plans to move her, which could have taken months or years.