Ocean Park mystified by sudden death of six hammerhead sharks
Nearly half of the hammerhead population falls victim to unidentified disease within hours
Six hammerhead sharks at Ocean Park died one by one in just seven hours yesterday because of a disease the park has not identified.
The remaining eight sharks "were also at risk", the park said, and its staff would continue to closely monitor them, segregating them and administering treatment if the need arose.
The dead sharks were first found "swimming abnormally" in the Grand Aquarium in the morning yesterday. They had shown no signs of illness before then, a spokeswoman said. Staff then moved them to a different area for treatment and observation, but from about 11am the sharks - all females weighing 45kg to 60kg - died one by one, until the last one perished at about 6pm.
The park's chief veterinarian Paolo Martelli said the park was experiencing high morbidity - the rate of incidence of a disease - with rapid mortality in the hammerhead shark population.
"We are now performing necropsies to better understand the cause of death," Martelli said, in a statement from the park issued yesterday evening.
The six dead sharks - all about five years old - were among the 15 hammerheads introduced from Japan in late 2010.
The park said that one had died already due to its inability to adjust to a new environment when it was moved into the Grand Aquarium in January 2011 from the old aquarium. But the other 14 "had doubled their weight and grown healthy over the past three years".
Ocean Park's spokeswoman said it had reported the death to the Agriculture, Fisheries and Conservation Department immediately. A spokeswoman for the department said it would follow up with the park on the matter.
According to Nimal Fernando, senior veterinarian at the park: "Dolphins can't really commit suicide. The mental ability to make a decision to kill yourself is beyond a dolphin's reasoning capability."
Samuel Hung Ka-yiu, a marine conservationist, said the dead fish were scalloped hammerhead sharks, which were listed as an endangered species by the International Union for Conservation of Nature.
"We'd warned the park not to introduce endangered species into its captive environment, no matter whether they are blue fin tuna or hammerhead sharks," Hung said. "I hope the park will learn a lesson from such a saddening loss."
Hung believes that the eight remaining hammerhead sharks are "in great danger", since the others died so suddenly. In June 2008, a sturgeon died at the park soon after being bitten by a barracuda kept in the same tank. Another sturgeon died six months later because of an infection induced by the poorly maintained tank water.