Thursday, 13 April 2017

How many dolphins are there in Hong Kong waters?



'Hong Kong population' of Chinese white dolphins re-defined
 
Date: April 11, 2017
Source: The University of Hong Kong

The latest study by researchers at the University of Hong Kong (HKU) delivered the first-ever comprehensive population assessment of the Chinese white dolphins that inhabit Hong Kong waters, and what they found differs from the common public belief. In fact "it differs very substantially from the estimates reported in Hong Kong for the past many years," said Dr. Leszek Karczmarski, Associate Professor at the Swire Institute of Marine Science and School of Biological Sciences, HKU, who has instigated and supervised this study. "Contrary to statements frequently repeated by various Hong Kong media, there is no such thing as 'Hong Kong dolphin population' " he added.

"The dolphins seen in Hong Kong waters represent an integral part of the Pearl River Estuary (PRE) population; they are not aware of the administrative border between Hong Kong and Mainland waters, frequently traverse these waters, and there are at least 368 dolphins that rely on Hong Kong waters as part of their home range," said Mr. Stephen Chan, a Ph.D. student in Dr. Karczmarski's Lab and the lead author of the study that was published in the peer-reviewed journal PLOS ONE.

How does it compare to the frequently advocated estimates of the apparently last remaining 60-something Hong Kong dolphins, reported by the dolphin monitoring program contracted annually by Hong Kong's Agriculture, Fisheries and Conservation Department (AFCD)?

Dr. Karczmarski explained: "There are several reasons for these considerable differences. The AFCD-funded monitoring program applies a sampling technique called line transect sampling which differs from photographic mark-recapture technique applied by the HKU team. These two techniques address a different albeit mutually relevant research question, and therefore the estimates they generate have different meanings, each with their own merits. While the line-transect approach estimates the number of animals that are present in the area at a given time, the mark-recapture analyses estimate the overall number of animals that use Hong Kong waters during the study period. The heart of the matter is how one interprets the results, and this is the part that has been highly problematic with the AFCD's data over past years."

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