A leading animal welfare charity claims that a polar bear "died from a broken heart" after her best friend of 20 years was shipped away from SeaWorld San Diego to Pittsburgh Zoo.

People for the Ethical Treatment of Animals (Peta) made the claims yesterday following the death of Szenja, a 21-year-old polar bear born in captivity and living in SeaWorld's Wild Arctic exhibit since the 1990s.

She lived alongside Snowflake in the enclosure for around 20 years and the two females developed a deep friendship. Recently Snowflake was sent to Pittsburgh Zoo in an attempt to breed her.

Now Szenja has died and Peta say the causes of death are abundantly clear.

"Szenja died of a broken heart, Peta believes. After losing her companion of 20 years when SeaWorld shipped Snowflake to the Pittsburgh Zoo in order to breed more miserable polar bears, Szenja did what anyone would do when they lose all hope, she gave up," said Peta Vice President Tracy Remain.

"This should be a wake-up call to SeaWorld: stop breeding and shipping animals around, close the animal exhibits, and retire the animals to sanctuaries. Until it does, this ship will keep sinking," Remain added, as reported in the Times of San Diego.

Polar bear
A polar bear looks out at visitors from his cage at San Diego's SeaWorld, 07 October 2007. Polar bears living in captivity are believed to suffer depression GABRIEL BOUYS / AFP / Getty Images

It is reported that Szenja lost her appetite in the days after Snowflake's departure but her death still came as a shock to SeaWorld staff.

Al Garver, SeaWorld's vice president of zoological operations said: "Szenja not only touched the hearts of those who have cared for her over the last two decades, but also the millions of guests who had a chance to see her in person.

"We're proud to have been a part of her life and to know that she inspired people from around the world to want to protect polar bears in the wild."

Polar bears can only expect to live until they are about 18 in the wild whereas those in captivity, such as Szenja, often live into their late 20s.

SeaWorld San Diego was previously criticised for mobilising employees to pose as animal rights activists to spy on its critics.