Won't somebody please think of the porpoises???

This post marks the introduction of a new theme here at standing-room-only: Impacts on Marine Ecology.

The 263 islands forming Hong Kong boast an incredible 733km of coastline leading to the expanse of the South China Sea. This setting provides an multitude of habitats for various marine fauna. WWF Hong Kong provides a great synopsis of marine biodiversity across the islands.

Perhaps the most noteworthy members of HK's marine ecology are the Chinese White Dolphin (Sousa chinensis) and the Finless Porpoise (Neophocaena phocaenoides). Whilst a total of 16 Cetacea species (Wikipedia) have been recorded in Hong Kong waters the White Dolphin and Finless Porpoise are the only members of this group that are spotted with enough frequency to be considered local species (Jefferson et al, 2009).

The Finless Porpoise, courtesy of the WWF.

• The Finless Porpoise is highly distinctive due to it lack of a dorsal fin (bet you didn't see that coming?), a unique trait amongst porpoises.

A distribution study carried out by Jefferson et al, 2002 observed that in the Hong Kong area the porpoises are limited to the southern and south-eastern waters and appear to traverse this area on a seasonal basis. It is thought that the porpoises' aversion to freshwater prevents their movement from straying further west where the freshwater outflow from the Pearl River Delta has a stronger influence on local salinity levels.  The study also notes that coastal areas with seasonally increased freshwater input (Southern Lantau island for example) cause the populations to avoid the area until salinity levels are recovered.

Between 1995 and 2000 the same study recorded that the abundance of the mammals in the HK area varied seasonally from approximately 55 observed members in autumn to over 150 in spring-time. It is thought that this fluctuation is caused by porpoise groups moving north-east into Chinese waters during the summer.

Chinese white dolphin, courtesy of actionasia.com

• The Chinese White Dolphin (also known as the Indo-Pacific Humpback Dolphin) has a light pink skin, a result of blood vessels close to the skin surface that are used to regulate the internal temperature of the mammal.

The White Dolphin appear to be the antithesis of the Finless Porpoise in regards to preferred habitat: they are present across all of Hong Kong's western waters and are rarely observed in HK's central-southern or south-eastern waters. The dolphin population is also known to extend north from western Hong Kong, following the freshwater influence of the Pearl River Estuary (Jefferson et al, 2009).

Further studies by the, now ubiquitous, Jefferson and Hung, 2004 recorded that although dolphin numbers in, and adjacent to, Hong Kong waters varied between 103 in spring to 193 in autumn, these variations were not reflected in the overall population. This suggests that, unlike the Finless Porpoise, the White Dolphin is a year round resident of HK waters.

The two species are known to coincide in just one area: the Soko Islands. Which may account for the recent government proposed plans to create a new marine park in the vicinity (Hong Kong Government, 2014).

Soko Islands (image courtesy of South China Morning Post). Read article here.

It is widely accepted that Hong Kong's marine ecology has suffered massive deterioration and is potentially on the verge of collapse (WWF website). The impact of large scale development across Hong Kong and China is negatively affecting, and in some cases completely obliterating the habitat for Cetaceans. Join me next time when we take a look at these impacts and how they are affecting the marine ecology.

Can't get enough Porpoises!