Taxonomy:

Both species belong to the Order Cetacea, but finless porpoise is categorized in the family “ Phocoenoide ” (True porpoise), while Chinese white dolphins in the family “ Delphinidae ” (Ocean dolphin).

Appearance:

Finless porpoise mother-and-calf pair - they are both gray

Porpoises are generally smaller, and finless porpoise is no exception. At birth finless porpoise is only around 70 cm long. And their length reaches 1.8 m at most in adult stage. On the other hand, Chinese white dolphin calf is around 1 m long at birth, and they can reach around 2.6 m in adult stage.

Besides, finless porpoise in Hong Kong does not have a stunning colourful life cycle as the Chinese white dolphin does. Finless porpoise calf is generally in light gray, and its colour darkens with age.

Dorsal fin / Beak:

As the name implies, “finless” porpoise has no dorsal fin. Instead, rows of denticles can be observed on their back. Chinese white dolphin does bear a prominent dorsal fin. Also, the finless porpoise does not possess a protruding beak, while, the Chinese white dolphin has a long and slender beak.

On the left is a stranded finless porpoise. It does not have a dorsal fin but only rows of denticles on its back. And it does not possess a protruding beak. On the right are the Chinese white dolphins, which have prominent dorsal fin and protruding beak.

Tooth:

As these two species belong to two different families in classification, their teeth are a lot different from each other. Teeth of finless porpoise are small and are spate-shaped; while teeth of Chinese white dolphins are large and sharper. Scientists believe this is related to their different feeding habit.

Upper row: tooth cross section of a Chinese white dolphin; Lower row: tooth cross section of a finless porpose

Behaviour:

Most members of porpoises are rather elusive, finless porpoise is no exception. They seldom surface, and disappear when there is any approaching vessel. On the contrary, Chinese white dolphin is much more playful. They perform lots of aerial behaviour on water surface, and approach vessels sometimes.

Can Finless porpoise still be divided into several types?

Yes. Nowadays cetacean experts worldwide are aware that there are three subspecies of finless porpoise ( Neophocaena phocaenoides ), including phocaenoides -type, asiaeorientalis -type and sunameri -type.

The main feature of phocaenoides -type finless porpoises is that they bear more than 10 rows of denticles on their back, making them called “wide-ridge type” as well. Those finless porpoises along Indian Ocean and in Hong Kong belong to this type. The other two types have only few denticle rows, making a prominent ridge, so they are referred to as “narrow-ridge type”. Those porpoises in Yangtze River, mainland China and Matzu in Taiwan belong to the asiaeorientalis -type, while those in Japan and South Korea belong to the sunameri -type (whose body colour is paler).

On the left is the "wide-ridge type" finless porpoise (phocaenoides)；On the right is the "narrow-ridge type" finless porpoise (asiaeorientalis), which comes from Yangtze River, China

Due to the differences in morphology among these types of porpoises, scientists considered them different subspecies. However, their taxonomy has to be confirmed later by more detailed genetic studies.

Where do the finless porpoises in Hong Kong live?

Purple dots on the map are where researchers have sighted the finless porpoises in the past years

Although finless porpoise and Chinese white dolphin are neighbours in Hong Kong , but their distribution is quite different. Finless porpoise are mainly distributed in waters off southern and eastern Hong Kong , so they rarely meet those Chinese white dolphins, which inhabit waters off western Hong Kong . It is believed that the distribution of the two species is related to their ecology. Finless porpoise prefer living in oceanic waters, while Chinese white dolphins like to dwell in estuaries.

In addition, there is some seasonal variation in distribution of finless porpoise in Hong Kong . In winter and spring months (from December through May), finless porpoise mostly occur in waters off southern Hong Kong, including south Lantau (from Fan Lau to Pui O), Soko Islands, Cheung Chau, Lamma Island and south Hong Kong Island. In summer and autumn months (from June through November), finless porpoise shifts offshore (to mainland Chinese waters). Some occur in east Hong Kong , including waters around Po Toi, Ninepin Islands and Sai Kung.

Do finless porpoises and Chinese white dolphins meet in Hong Kong ?

Both finless porpoise and Chinese white dolphin are indigenous residents of Hong Kong . However, one can tell that they seldom see each other from their distribution. Finless porpoise never occurs in west Hong Kong , and Chinese white dolphin is hardly ever spotted in east and southeast Hong Kong .

The red and blue dots on the map represent where researchers have sighted the Chinese white dolphin and the finless porpoise respectively in Hong Kong and nearby waters in the past years

But according to the distribution map of both species below, you may find that both species use waters off southern Lantau. Actually, their distribution never overlaps in temporal scale. Finless porpoise leaves south Lantau by wet season (around summer and fall). At this time, Chinese white dolphin enters south Lantau; while by dry season (around winter and spring), when finless porpoise returns to south Hong Kong, Chinese white dolphin vanishes.

So why do they seem to avoid each other? Are they foes to each other? In fact, to date there have been evidence showing that they are evading each other. Instead, scientists leave their distribution is related to their feeding habit. In wet season, the freshwater outflow from the Pearl River into estuary is stronger, and more regions are influenced by the outflow (including south Lantau). So, Chinese white dolphins will follow their estuarine prey to south Lantau, while finless porpoise, being oceanic, avoids areas influenced by freshwater outflow. In dry season, south Lantau is less influenced by freshwater outflow, so Chinese white dolphin leaves, while finless porpoise comes in for breeding and calving.

How many finless porpoises are there in Hong Kong ?

During 1998-2000, a two-year-and-a-half survey for finless porpoise has been carried out. It is estimated that there are around 217 finless porpoises dwelling in Hong Kong and nearby regions. However, this figure has not been updated ever since, so we have no idea if there is any increase or decline in the porpoise abundance in recent years. Actually, only few field surveys have been carried out on porpoises in Hong Kong and South China. Therefore, not much can be done about their conservation.

Life cycle of a porpoise

Newborn calf of finless porpoise is very small, which is around 70 cm long. They can be 1.8 m long at adult age. The porpoises do not exhibit dramatic colour change throughout their life cycle. Newborn calf is usually in light gray, and their body colour darkens with age.

On the left is a finless porpoise calf, which is in light gray: on the right is an adult finless porpoise, which is in darker gray

Male porpoises become sexually mature when they are 4-5 years old, while females become so 5-6 years old. Since then they can start to mate and breed. They usually breed in winters, echoing the fact that number of porpoise in Hong Kong reaches the highest in winter and spring. Researchers hence speculate that porpoises in Hong Kong breed and nurse their young in inshore waters in south Hong Kong at winter and spring time.

Some research results show that growth rate of finless porpoise is the highest in the first few years after birth, which slows down afterwards. Finless porpoise is generally 20-30 years old, while the oldest animal recorded so far is 33 years old.

Where else can we find finless porpoise besides Hong Kong ?

Finless porpoise's diet

Food remains found in a finless porpoise's stomach , including shrimp and squid.

After analyzing stomach contents of those stranded porpoises in Hong Kong , researchers found that finless porpoises like to feed on a wide variety of fish species, numbering over 20 species, which include anchovies and cardinalfishes. Other than fish, porpoises prefer cephalopods (e.g. squid) and crustaceans (e.g. prawns) as well. This is quite different to Chinese white dolphin, which seems not like cephalopods and crustaceans.

Finless porpoises in Hong Kong are now facing a number of survival threats:

Sham Wan of Lamma Island is one of the finless porpoises' habitat ranges

Habitat degradation:

As coastal development in Hong Kong becomes rapid in the last few years, finless porpoises living in remote areas are eventually affected. In the next few years, it is very much likely that a Liquefied Natural Gas (LNG)Terminal will be established on Soko Islands , which are located south of Lantau Island . Reclamation and construction involved in this project pose potential threat to the porpoises which resides in South Lantau in winter to spring. Also, in the future an offshore wind farm may be established in waters around Ninepin Islands and Lamma Island, which may affect those finless porpoises living nearby.

This porpoise, which is found with fishing net rope scar, is a victim of fishery bycatch.

Fishery Bycatch:

In the past, scars caused by fishing net entanglement have been observed on some porpoise carcasses in Hong Kong . Some carcasses are even found with the fishing net, implying that fishery bycatch is a potential threat to the porpoises.

Vessel strike:

South Hong Kong is the main shipping channel for the high-speed ferries traversing Hong Kong and Macau . As in winter and spring more finless porpoises move to south Hong Kong , it is probably that they can be hit or even killed by vessel collision.

Water pollution:

The impact of pollutants in seawater imposed on the finless porpoises should not be overlooked. It has been found that specimens from finless porpoise carcasses in Hong Kong contain high level of organo-chlorinated compounds (e.g. PCB and DDT) and heavy metal (e.g. mercury). It is believed that these contaminants will negatively affect their health.

Conservation status of finless porpoise worldwide

Those finless porpoises at Matzu Islands, Taiwan are much threatened by gillnet entanglement.

Up to date, the species finless porpoise has been categorized as “ Data Deficient ” by the IUCN Red List of Threatened Species. This means that data for judging if this species is threatened is not sufficient. However, one of the subspecies of finless porpoise - asiaeorientalis -type, has been classified as “ Endangered ”, as the major habitat for this subspecies, Yangtze River, has been severely degraded, making number of porpoises in that area plummeting.

In addition, the CITES has listed finless porpoise in Appendix I, which means international commercial trade of finless porpoise is prohibited. Also, finless porpoise is legally protected in some range areas, such as Hong Kong, mainland China, part of the Inland Sea of Japan and Taiwan. However, the implementation of the legislation is generally weak, offering only limited protection to the species.

Overall, the finless porpoise is in no immediate danger of global extinction as they are widely distributed in the world. But several populations are probably threatened, including those in Yangtze River and the Inland Sea of Japan. Some others have probably been lost before they could be documented.