At least five dolphins, including a rare Chinese white dolphin, died during the Lunar New Year period.

It is feared they were hit by motorboats as they had injuries on their heads and necks.

Cetacean Virtopsy Lab, a dolphin concern group, posted on its Facebook page about five dolphins that had been found stranded between last Saturday and Monday. They were a white dolphin and four finless porpoises.

Autopsy scans found food remains in the dolphins, showing they were not starved to death. However, they showed multiple fractures.

One finless porpoise was almost cut in half and it is believed that the fatal wound was made by a boat propeller.

Last Saturday an adult Chinese white dolphin was found stranded at Mo To Chau. The 2.5-meter female was at least 10 years old, with signs of choking, bone fractures and serious bone dislocation.

The lab said the survival of adult dolphins is critical for the species. The death of an adult female is a great loss to the endangered species' population growth.

The lab also said there were only three to four stranded cetaceans discovered in January and February in the past three years. However, more than 10 dead dolphins have been discovered in the same period this year.

Samuel Hung Ka-yiu, founder and chairman of the Hong Kong Dolphin Conservation Society, said high-speed boats have always been a big threat to dolphins and some of the aquatic mammals might be hit by propellers and chopped into pieces without being discovered.

He said he had urged the government to launch a speed restriction on boats around dolphin habitats or even ban them from entering the area.

"But the Marine Department has never considered our concerns," he said. "I hope these tragic events show them we need to change our policies in order to protect our dolphins."

Hung said dolphin concern groups found only one new-born Chinese white dolphin last year.

The death of an adult female dolphin is a massive loss as she could have been a mother, he said.

jane.cheung@singtaonewscorp.com