54 stingrays die at Chicago-area zoo after tank snafu

And just like that, they were gone.

All 54 of a Chicago-area zoo's stingrays died Friday after oxygen levels dropped in the animals' tank. Officials from Brookfield Zoo said staff responded to an alarm set off by the zoo's Aqua Net System, which monitors temperature, ozone and oxygen levels. Veterinarians arrived at the scene, and staff took the animals to the zoo's animal care unit in an attempt to save them.

"We are devastated by the tragic loss of these animals," said Bill Zeigler, senior vice president of animal programs for the Chicago Zoological Society, which operates the zoo, in a press release on Sunday. "Our staff did everything possible to try and save the animals, but the situation could not be reversed."

Four southern stingrays and 50 cow-nose rays died in the incident and they were all born in captivity, according to Zeigler. He said several pumps were placed in the pool to fix oxygen levels, which were restored after 20 minutes after the alarm rang.

Despite the fix, the stingrays still died.

Zoo officials are still investigating the cause for the malfunction.

The exhibit, called Stingray Bay, will be closed for the remainder of its summer season, according to the zoo's Facebook page. The venue opened in 2007.

The exhibit allows visitors to interact with the stingrays by touching or feeding them. More than 200,000 people visited the exhibit last year.

Zeigler told USA TODAY the staff will decide whether or not to open another stingray exhibit next summer after assessing the cause of the accident. He said the staff is deconstructing the exhibit, collecting sand from filters and testing water quality on parts of the system, among other measures, to determine the cause.

This isn't the first time the zoo's stingray exhibit faced hardship. In 2008, 16 stingrays died after a malfunction in the pool's heating and cooling system.

Brittany Peet, deputy director of captive animal law enforcement for People for the Ethical Treatment of Animals (PETA), told the Chicago Tribune these interactive exhibits are "death traps."

"At this point, 70 animals have died at the Brookfield Zoo as a result of malfunctions with their tank and it's time for them to close down their tank for good," she told the Sun-Times. "Their lives are worth more than the cheap thrill of touching one of the these animals."

Zeigler said in 2008, the accident only took the lives of a portion of the stingray population. The event Sunday was a bit more dramatic, as it wiped out the whole group.

Commentators on the zoo's Facebook announcement said it is the zoo's responsibility to ensure animals are safe at all times.

"However with this being the second system failure in a handful of years I'm wondering if the zoo should give the stingrays a more permanent habitat in the zoo and abandon the touch exhibit," wrote Michelle Diane.

Others were more understanding of the incident, and offered their condolences.

"My heart is with every employee of the zoo; this is such a tragic loss of life, and I will continue to support the zoo and their beautiful animals," wrote Rachel Scott.

Zeigler said the zoo has received mostly positive comments from patrons of the zoo and Facebook fans.

"Our staff is still hurting after the incident," Zeigler said. "So far, the community has been very supportive."