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Chinese White Dolphin

Hong Kong scientists lock horns over dolphin population size, with new HKU study finding larger numbers

Leading expert says the latest data could lead the government to underestimate threat of human activities

PUBLISHED : Friday, 31 March, 2017, 10:09pm
UPDATED : Friday, 31 March, 2017, 11:25pm

A new study by the University of Hong Kong has found that at least 368 Chinese white dolphins rely on the city’s waters as part of their home range – a larger number than previously estimated.

But the scientist who has been the city’s authority on monitoring of the endangered species has warned against over focusing on the research, when forming policy.

The study, published in peer-reviewed journal PLOS ONE, was conducted between 2010 and 2014, and co-authored by Stephen Chan, a PhD student, and Dr Leszek Karczmarski, associate professor at the Swire Institute of Marine Science and School of Biological Sciences.

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Chan noted that the dolphins in Hong Kong waters represented an integral part of the Pearl River estuary population.

In 2015, 65 Chinese white dolphins were estimated to be in Hong Kong waters, while the figures from 2010 to 2014 were between 73 and 88, according to reports by the Agriculture, Fisheries and Conservation Department.

Dr Karczmarski said that the far lower numbers recorded by the department was because it took estimates of animal populations that were present in the area at a given time, while his team looked at the overall number of animals in Hong Kong waters throughout the study period.

The authors said the department’s technique could only sample “a portion of the population range”.

Chan added: “For example, counting every person in Hong Kong on any particular day does not represent the population of Hong Kong, because there are lots of tourists, visitors and even residents travelling in and out.”

But Dr Samuel Hung Ka-yiu, chairman of the Hong Kong Dolphin Conservation Society – which conducts the monitoring reports for the department – said his team surveyed each area 40 to 50 times, and therefore their data was accurate.

Dr Hung said his study could identify annual trends, which was not presented in the HKU paper.

“This could, for example, give us an idea of the effect of the Hong Kong–Zhuhai–Macau bridge on dolphins,” he said.

The scientist added that the HKU technique might overestimate dolphin numbers as animals that only came to Hong Kong once a year were also recorded.

Dr Hung warned: “The HKU study could cause the Development Bureau to view the issue of dwindling dolphin numbers lightly.”

A spokeswoman from the Agriculture, Fisheries and Conservation Department said it focuses on monitoring changes in dolphin numbers. She also said the department’s technique could be used to estimate the average number of dolphin appearances at a particular time.

Environmentalists have been vocal in their concerns over the effect on dolphin numbers brought about by projects like the Hong Kong–Zhuhai–Macau bridge and a third airport runway.