Chicago’s Brookfield Zoo is trying to figure out what may have caused a drop in oxygen that killed four Southern stingrays and 50 Cownose stingrays last Friday. Emergency notifications from the system that monitors oxygen and ozone levels went out around 1:45pm on Friday and a manager was onsite within minutes. The rays were located in a shallow touch pond style pool so immediate efforts were made to increase the oxygen levels with the use of oxygen pumps and submersible air lines. The senior vice president of animal programs for the Chicago Zoological Society that operates the zoo comments: “We are devastated by the tragic loss of these animals. Our staff did everything possible to try and save the animals, but the situation could not be reversed.” Each stingray loss on Friday was bred in captivity yet the exhibit has encountered equipment failures in the past resulting in the loss of rays. “We had a malfunction of a different type back in 2008. It was a water temperature increase, and the exhibit temperature increased by about 10 degrees, and we lost about 16 stingrays in that,” added spokeswoman Sondra Katzen. Read more here.