(CNN) -- The film "Blackfish" compellingly describes many of the reasons why keeping orcas in captivity is -- and always has been -- a bad idea.
The main premise of the film is that these large, intelligent, social predators are dangerous to their trainers. But orcas are also directly harmed by being confined in concrete tanks and the science is growing to support this common sense conclusion.
The latest data show that orcas are more than three times as likely to die at any age in captivity as they are in the wild. This translates into a shorter life span and is probably the result of several factors. First, orcas in captivity are out of shape; they are the equivalent of couch potatoes, as the largest orca tank in the world is less than one ten-thousandth of one percent (0.0001%) the size of the smallest home range of wild orcas.
Second, they are in artificial and often incompatible social groups. This contributes to chronic stress, which can depress the immune system and leave captive orcas susceptible to infections they would normally fight off in the wild.
Third, they often break their teeth chewing compulsively on metal gates. These broken teeth, even drilled and cleaned regularly by irrigation, are clear routes for bacteria to enter the bloodstream. These are the obvious factors; there are almost certainly others contributing to the elevated mortality seen in captivity.
These factors boil down simply to this: Captivity kills orcas.
Yes, they may survive for years entertaining audiences, but eventually the stressors of captivity catch up to them. Very few captive orcas make it to midlife (approximately 30 years for males and 45 for females) and not one out of more than 200 held in captivity has ever come close to old age (60 for males, 80 for females). Most captive orcas die while they are still very young by wild orca standards.
There is a win/win solution to both the trainer safety and orca welfare dilemmas facing marine theme parks around the world, including SeaWorld in the United States.
These facilities can work with experts around the world to create sanctuaries where captive orcas can be rehabilitated and retired. These sanctuaries would be sea pens or netted-off bays or coves, in temperate to cold water natural habitat. They would offer the animals respite from performing and the constant exposure to a parade of strangers (an entirely unnatural situation for a species whose social groupings are based on family ties and stability -- "strangers" essentially do not exist in orca society). Incompatible animals would not be forced to cohabit the same enclosures and family groups would be preserved.
Show business trainers would no longer be necessary. Expert caretakers would continue to train retired whales for veterinary procedures, but would not get in the water and would remain at a safe distance (this is known in zoo parlance as "protected contact"). And the degree to which they interact directly with the whales would be each whale's choice.
A fundamental premise of these sanctuaries, however, is that eventually they would empty. Breeding would not be allowed and captive orcas would no longer exist within the next few decades.