Chinese White Dolphin - Threats

The population of the Chinese white dolphins in the Pearl River Estuary (PRE) is very unique. Not only is it the largest one that remains along China’s coastline, it also inhabits one of the world’s most congested areas that has very heavy marine traffic and serious water pollution problems. The dolphins that inhabit these areas are under enormous pressure. Due to a series of development projects, they are facing severe man-made threats that have resulted in habitat loss and degradation.
Fishing Boat near Chek Lap Kok
© Adam Minu
Since the mid-90s, more than 1,400 hectares of sea area have been reclaimed in Hong Kong’s western waters. This is within the relatively small area inhabited by the dolphins. In addition to a direct loss of the dolphin’s habitats, reclamation has affected fishery resources, which subsequently leads to a decrease in food supply for the dolphins. The threats to our vulnerable marine ecosystem don’t end with reclamation. Additional threats include past, present and future works on dredging; dumping; and facilities installation. As well, the impacts from water and noise pollution, and an increase in vessel traffic, play a role in destroying the habitat.

Agriculture, Fisheries and Conservation Department (AFCD) has a Chinese white dolphin conservation programme and action plan. However, apart from conducting a long-term monitoring programme, progress is limited to implementing the conservation measures identified when plan was formulated back in 2000. For instance, although the Sha Chau and Lung Kwu Chau Marine Park, the so called “dolphin sanctuary,” is a key component of this conservation plan, its effectiveness may be limited as the area is not truly protected from development and habitat modification. The marine park should also provide increased feeding opportunities for the Chinese white dolphin population by allowing fish and other food stocks to increase. Commercial fishing under permit is still allowed within the marine park, however, so the dolphins are competing with fishermen for food. After all, at least three important habitats for the dolphins are not receiving any statutory protection.

The Chinese white dolphin population in Hong Kong and the PRE are specifically facing the following major threats:
1. Habitat Loss from Coastal Development
Chinese white dolphins typically feed in shallow coastal areas up to a depth rarely exceeding 10 metres. Extensive reclamation for many past, current and future projects such as the Hong Kong International Airport, Hong Kong-Zhuhai-Macao Bridge, and the third airport runway is physically reducing the recognized dolphin important habitats. This adds a stress upon the dolphin population, forcing them to move farther away, possibly towards less suitable habitats. Habitat loss from rampant coastal development directly results in the loss and disturbance of the Chinese white dolphin’s breeding, nursery and foraging grounds. Reclamation may also block or affect movement between important habitats.

2. Water Pollution
The amount of suspended solids in the water column elevates during the dredging process. An increase in suspended solids raises the risk of clogging fish gills. As well, it reduces growth rates and prevents egg and larval development. Fish and some crustaceans are known to be the major food source of dolphins; an increase in sediment will subsequently lower the amount of food available for the dolphins and threaten the food chain. The dredging works may also lower the dissolved oxygen concentration in the water column, causing death of the fish and also resulting in a reduction in the food source available to Chinese white dolphins.

The dumping work at the contaminated mud pits, namely the existing East Sha Chau facility and the future South Brothers facility, may also pose adverse impacts to the Chinese white dolphin habitats in the surrounding areas. Pollutants such as organochlorines and heavy metals from the contaminated mud will dissolve into the water column and accumulate in dolphins’ bodies, which are considered potentially health threatening for the Chinese white dolphin.

The Chinese white dolphin has also suffered from the regional water pollution of the PRE. However, the overall impacts of water pollution to dolphin are remained unclear and more research is required.

3. Underwater Noise Pollution
Dolphins rely on echolocation, which is similar to sonar, for hunting, communication and navigation. The dolphins listen to the reflected sound they produce and use this to locate their peers, fish and other objects. Underwater construction works sometimes involve techniques such as percussive piling (which will be used for constructing the foundation of wind turbines in south Lamma), which may interfere with the dolphins’ echolocation capability. In extreme cases, this will result in death for the affected dolphins.

The increasing marine traffic also poses threats of obscuring sounds and acoustic communication, also interfering with echolocation. High levels of boat noise can lead to injuries or disturbance, as manifested by changes in behaviour and use of acoustic signalling.

4. Vessel Collision
In Hong Kong, the waters have become more congested due to reclamation, and marine traffic is also getting busier. There are many high-speed ferries running between Hong Kong, Macau and other cites in the Pearl River area everyday. The marine traffic has increased in western waters, doubling from 1999 to 2009. The current high-speed ferry routes transverse the prime dolphin habitats around Lantau waters, increasing the risk of dolphins being hit and causing injuries. Scars and marks, possibly caused by the vessel propellers, can sometimes be observed on the fins or bodies of the Chinese white dolphin.

5. Over-fishing
In Hong Kong, there are no regulations in place to control fishing efforts or the available catch. A continued decline in fisheries resources have been observed. Local catch composition has changed from mainly large, slow-growing, high-value species, to small, fast-growing, low-value species. In additional to over-fishing, certain fishing practises are also not sustainable. For instance, the seabed is continually disturbed by bottom trawling. The decline in fisheries resources will cause reduction in food supply to the dolphins.
Chinese White Dolphin
© Alan Leung

Information About Stranded Dolphins

The cause of death for most of these individuals is largely unknown, although entanglements with fishing gear, injury from vessels and high pollution levels have been responsible for several deaths. The majority of deaths are of young or newborn dolphins.

Below is the number of Chinese white dolphins stranded between 2000-2009:

No. of Chinese White Dolphin strandings
2000 10
2001 8
2002 7
2003 14
2004 10
2005 13
2006 5
2007 17
2008 10
2009 8

Source: Agriculture, Fisheries and Conservation Department