34 Stingrays Die At Calgary Zoo

Calgary — As nine surviving stingrays, some covered with black blotches – a telltale sign of stress – slowly swam around a temporary holding tank at the Calgary Zoo yesterday, officials were scrambling to determine what wiped out 34 others in a matter of hours.

The cownose stingray exhibit, which opened in February and allows visitors to touch and feed the fish in their 10,000 gallon tank, is closed as staff await test results on water, food and tissue samples from the dead rays.

But the circumstances are so mysterious, so sudden and so unusual that zookeepers aren't ruling out foul play.

“It's hard to speculate, but certainly you have to look at was something introduced through the water lines? Was something introduced into the pool? Did someone put something in there?” said Doug Whiteside, a zoo veterinarian who performed necropsies on the rays and found irritants in their gills, which suggests something toxic might have been in the water.

“I don't think there is anything innocent that would be able to kill that many rays in a tank of that size,” he added.

In-house tests showed that the water was within “normal” parameters. But it could take up to two months for toxicology results.

The baby rays, which are about the size of a dinner plate and weigh one kilogram – but can grow to more than 10 times that size – were healthy, eating and swimming normally in the 25 C water on Sunday morning.

At 1 p.m., three hours after the exhibit opened to the public, they started losing their appetite. At 3 p.m., the colour of some of the rays had changed. Water testing was done, but the results were not suspicious. Then, some began swimming erratically. By 4:20 p.m., the ray keeper noticed several creatures in “extreme distress” and, 10 minutes later, several were floating dead in the pool.

That's when the exhibit was closed and the remaining rays were quickly moved to holding tanks with oxygenated water in order to increase the flow of oxygen through their gills.

By 5:30 p.m., 26 rays were dead. The remaining 17 appeared to be in stable condition, but by early yesterday morning, eight more had died and the survivors were in guarded condition.

Cathy Gaviller, the zoo's director of conservation, research and education, said there was no mechanical failure in the life-support system of the tank, which maintains water filtration, temperature and chemistry levels.

Last year, 21 stingrays died at the Fresno Chaffee Zoo in California when a power failure caused systems to malfunction, which in turn dramatically altered the water in their tank.

In Calgary, as in many other zoos and aquariums across North America, visitors are allowed to place their hands in the pool to touch the rays, which, despite their name, pose no threat to visitors because their tale barbs have been trimmed.

Signs and staff members asks patrons to wash their hands before placing them in the tank– but they are not required to – and they are told to remove watches, rings or any metal, although some people don't.

Officials said yesterday they don't think hand cream, nail polish or contact with jewellery is to blame, but that the introduction of even a tiny amount of toxin might be. There are surveillance cameras around the exhibit, but they don't monitor the entire tank area and staff didn't report seeing anything suspicious on Sunday.