SAN DIEGO (Reuters) - SeaWorld said on Thursday it will stop breeding killer whales in captivity, bowing to years of pressure from animal rights activists, but the orcas already at its three parks will continue performing as they live out their remaining years.

Slideshow ( 5 images )

SeaWorld Entertainment Inc's SEAS.N decision came after it pledged in November to replace its signature "Shamu" killer whale shows in San Diego with modified presentations of the animals that focused on conservation.

“We don’t need all these theatrical ‘tricks,’” SeaWorld President Joel Manby said on a conference call with reporters. Manby said the parks will use birth control to halt reproduction among its killer whales, also known as orcas.

SeaWorld, which operates marine parks in San Diego, Orlando and San Antonio, has a total of 29 killers whales, including six on loan to a park in Spain. Five of them were captured in the wild, but it has not caught orcas at sea for almost 40 years.

The parks have been criticized for their treatment of the captive marine mammals, with some activists seeking an end to public exhibition of killer whales altogether.

The criticism intensified after three orcas died at SeaWorld San Antonio within a six-month span in 2015. In a statement responding to the deaths, the company said: “We have the highest standard of care for all animals at our parks.”

The life span of a killer whale in the wild is typically 30 years for males and 50 for females, with some females living as long as 100 years, according to the website of the National Oceanic and Atmospheric Administration. SeaWorld’s oldest killer whale, Corky, is a 51-year-old female.

SeaWorld, whose shares rose 8.2 percent on Thursday, also said it will scrap plans for a $100 million project called “Blue World” to enlarge its 7-million-gallon orca habitat at SeaWorld San Diego.

Some activists have called for SeaWorld to release its orcas into coastal sanctuaries, but the company says whales born or raised in captivity would likely die in the wild.

SeaWorld faced mounting criticism after the release of the 2013 documentary “Blackfish,” which depicted the captivity and public exhibition of killer whales as inherently cruel.

“The fact that SeaWorld is doing away with orca breeding marks truly meaningful change,” said Gabriela Cowperthwaite, director of “Blackfish.”

Animal rights group People for Ethical Treatment of Animals said SeaWorld had taken a step forward but renewed a call for the company to link its tanks to ocean sanctuaries.

Under the new plan the orcas will still be shown to visitors at set times, but viewing areas will be reconfigured to “reflect the natural world” with a program focusing on “orca enrichment, exercise and overall health,” according to the SeaWorld website.

SeaWorld also said it will partner with the Humane Society of the United States and had set aside $50 million to push for an end to commercial whaling and seal hunting as well as the killing of sharks for their fins over the next five years.