An orca was born at Orlando's SeaWorld this weekend, heralding some good news for officials concerned about the mortality rate of the huge marine mammals kept at the Florida theme park.

A 25-year-old orca named Kalina was found dead Monday night, the fourth killer whale to die at SeaWorld Orlando in the past four months.

Marine biologists are trying to determine why the whale died, but the case has already raised the ire of animal rights activists.

Bryan Wilson, of the group People for the Ethical Treatment of Animals, told NBC News that the conditions under which Kalina was kept undoubtedly contributed to her death.

"She has an artificial diet … is living in chemically treated water in an environment that puts tremendous stress on their bodies," Wilson said.

He said wild orcas are used to roaming freely through vast areas of oceans, making even the huge tanks where they are kept at SeaWorld seem comparatively tiny.

"They are living in a tank that to you and I would be considered a bathtub."

The theme park has issued a statement denying that the whales died as a result of conditions at SeaWorld. "Animals in our care live and die as do those in the wild … We have no reason to believe their environment was a contributing factor."

SeaWorld said there have been 26 successful births in the last 25 years, and 17 of the 26 killer whales have been born alive in SeaWorld parks. Their oldest orca is Corky, a 43-year-old female at the San Diego SeaWorld.

SeaWorld says the four most recent deaths are unrelated, however they have not released necropsy reports into the causes of death.

The death of Kalina, the first orca born into captivity at a SeaWorld park, was undoubtedly a blow to the theme park's breeding program.

And she is only the latest in a recent string of killer whale deaths. In September, SeaWorld San Diego lost a 12-year-old male orca whale, Sumar. Pregnant female Taima died while giving birth to a stillborn calf at SeaWorld Orlando in June.

A total of 24 killer whales have died in captivity at the three SeaWorld resorts since 1985, ranging in age from less than one year to 30.

Not a single captive orca has lived past 30 years old. "That's not even middle-aged for wild orcas," said Naomi Rose, a marine mammal scientist for the Humane Society of the United States.

Killer whales can live to be between 60- and 80-years-old in the wild.

This has been a tragic year for SeaWorld. In February Tilly, an orca whale with 25 years in captivity grabbed trainer Dawn Brancheau's ponytail and dragged her underwater to her death.

SeaWorld was fined $75,000 by the United States Occupational Safety and Health Administration, however they have filed an appeal.

Rose said that the deaths are a signal that SeaWorld has failed in its attempts to keep and breed orcas in captivity. "It is difficult to escape the conclusion that a 45-year experiment has resulted in a spectacular failure," she said.

"SeaWorld has spent decades trying to convince the world that, contrary to all logic, such a creature belongs in small concrete tanks. The evidence has been mounting for at least 25 years that this is flatly untrue and the events of 2010 should be the final word."

With files from CTV's Paul Workman