54 stingrays dead after habitat malfunction at Chicago’s Brookfield Zoo

Brookfield Zoo officials said all 54 stingrays in the zoo’s Stingray Bay habitat died Friday after oxygen levels dropped in the tank in which the animals lived.

The zoo’s Aqua Net System, an alarm that monitors temperature, ozone and oxygen levels, went off at about 1:45 p.m. Friday. A 24-hour manager was automatically alerted by the system through his phone and responded immediately to the exhibit, said Bill Zeigler, senior vice president of animal programs for the Chicago Zoological Society.

The manager was met at the tank by the zoo’s veterinary staff and the zoo’s animal care unit. The staff then noticed the stingrays were behaving oddly, and immediately began attending to the animals, working to get the tank’s oxygen levels back to normal, Zeigler said. They also closed the exhibit, escorting visitors from the area.

An air bubbler that releases pure oxygen was added to the holding pool, followed by submerged air pumps to create a fountain effect. Lastly, a large oxygen pump was placed in the pool. Oxygen levels were restored in about 20 minutes from the alarm sounding, Zeigler said.

Despite the staff’s efforts, four southern stingrays and 50 cow-nose rays died, according to a statement from the Chicago Zoological Society, which operates the zoo. All of the animals were born in captivity, said Zeigler.

The stingrays were in a saltwater shallow pool that allowed guests to touch and feed the animals, officials said. The oblong-shaped pool is about 80-by-26 feet long and three feet deep, said Zeigler.

Most of the 54 deaths occurred between 3 and 4:30 p.m. Friday afternoon, but several died later in the evening, zoo officials said.

“We are devastated by the tragic loss of these animals,” Zeigler, senior vice president of animal programs, said in a release. “Our staff did everything possible to try and save the animals, but the situation could not be reversed.”

Staff at the zoo are analyzing the life-support system to determine the cause of the malfunction.

“They are taking it apart piece by piece to see what went wrong,” said Zeigler.

The Chicago Zoological Society has decided to close the exhibit, which has been at the zoo since 2007, for the rest of the summer.

In 2008, the zoo lost 19 stingrays when a heater unit malfunctioned, spiking water temperatures up by about 10 degrees, but Zeigler said that loss doesn’t compare to the Friday deaths. In the 2008 incident, 14 rays, eights sharks and three horseshoe crabs survived.