A toxin has been determined to be the cause of death for two beluga whales at the Vancouver Aquarium. The aquarium says a five-month investigation in the deaths determined that the toxin was likely introduced by food, water or through human interference. But the probe did not identify the exact substance responsible for the deaths of 21-year-old Qila and her mother, 30-year-old Aurora, in November. The aquarium says it’s taking steps to protect the remaining animals at the aquarium by enhancing food screening, overhauling its water treatment systems and upgrading its security monitoring.