The Stingrays of Hong Kong

I have just added a page about all the different species of ray that are found in Hong Kong. Here is a little preview on just the stingrays. Check out the full list of rays here.

The Stingrays of Hong Kong:


Round ribbontail Ray / Black-spotted stingray (Taeniura meyeni)

Round Ribbontail Ray (via WikiCommons)
Round Ribbontail Ray (via WikiCommons)
A bottom-dwelling inhabitant of lagoons, estuaries, and reefs, generally at a depth of 20–60 m (66–197 ft). Reaching 1.8 m (5.9 ft) across. Generally nocturnal, the round ribbontail ray can be solitary or gregarious, and is an active predator of small, benthic molluscs, crustaceans, and bony fishes. Although not aggressive, if provoked the round ribbontail ray will defend itself with its venomous tail spine. In Hong Kong, it is found mainly in the relatively clear southern and eastern waters, but it has also been found in the northern part of Lantau and in brackish water near the Pearl River estuary. It is also one of the species that has been found on Hong Kong’s artificial reefs. Check out Eric Keung’s spooky photo of a this stingray in Hong Kong waters.
Between July 2005 and June 2008 there were two cases of people being stung by stingrays in HK – fortunately with mild outcomes. The sting and its venom can cause bluish or greyish discoloration around the wound, disproportionate pain, muscle cramp, weakness, seizure, hypotension, cardiovascular toxicity, deep wounds and lacerations. In other words, stingrays are dangerous! Just watch from a distance and don’t touch!

Blue-Spotted Stingray (Neotrygon kuhlii)

Blue-Spotted Stingray, Papua New Guinea (via WikiCommons)
Blue-Spotted Stingray, Papua New Guinea (via WikiCommons)
The body is rhomboidal and green with blue spots with a maximum width estimated at 46.5 centimeters (18.3 in). The rays coloration is a warning for the highly poisonous barbs, thus few animals attempt to overpower this ray. In HK, they are more easily seen in summer in the shallow water along the coast, on coral reefs and in mangrove areas. Because of the venomous sting observers should not get too close or try to touch it!

Pale-edged stingray (Dasyatis zugei)

Pale-edged Stingray (via WikiCommons)
Pale-edged Stingray (via WikiCommons)
A bottom-dwelling ray most commonly found over sandy areas shallower than 100 m (330 ft) and in estuaries. It measures up to 29 cm (11 in) across, has a diamond-shaped pectoral fin disc, a long projecting snout, small eyes, and a whip-like tail. It is chocolate-brown above and white below and feeds mainly on small crustaceans and fishes. In HK it is mainly found in the western Pearl River estuary south of Lantau Island.

The Tai Po Whale of 1914 and the Taipo Whale of 2014

I found another ‘gem’ while looking through old HK newspapers:

A Whale Now!

A reader informs us that a whale 23 feet [7m] in length was seen in Tolo Harbour, near Taipo, on Sunday [11th of May 1914], and that the police, from a launch, fired three rounds at the mighty creature, which however disappeared.”

Taken from the Hong Kong Telegraph 13th of May 1914
Taken from the Hong Kong Telegraph 13th of May 1914
How strange to think that back then the first reaction on seeing a big whale, was to pull out a gun and shoot it!

It struck me as quite interesting, that Tolo Harbor near Taipo was also the site the stranding of a 42-foot (13m) Omura’s whale in March 2014 – almost exactly 100 years later!

Tolo Harbor is almost completely enclosed by land so any whale erring into it is bound to get confused, I think.

Extinct in hong Kong – the Maxima Clam (Tridacna maxima)- ?

The giant clam Tridacna gigas which can grow to 120 in width and 200 kg in weight is one of a group of clams called giant clams – the Tridacnids. Although T. gigas is the biggest of them, there are others which are still pretty huge by clam standards. One of these giant clam species, the Maxima clam Tridacna maxima, used to occur in Hong Kong. It grows to about 40 cm width, though typically is only around 20 cm in width. But consult the IUCN records for this clam species and you will see that although it occurs throughout the tropical and sub-topical waters of the Indian and western Pacific Oceans, the entry for Hong Kong sadly reads ‘regionally extinct’. When did that happen? Why did they vanish? These are the questions I wanted to find answers to.

When did it go ‘regionally extinct’?

The first entry I could find for the Maxima clam being regionally extinct in Hong Kong is 1983. Unfortunately that’s about all I could find. But at it has been gone from Hong Kong since at least 1983. Unless of course it has returned….its a slow-growing animal but has a very wide dispersal through free-floating larvae that live in the plankton – that’s why it occurs over such a wide geographical area spanning nearly a quarter of the planet! So theoretically, if conditions are right (see more below) and larvae are swept over Hong Kong or are purposely introduced by humans, the Maxima clam could reestablish itself in Hong Kong.  So the next question is why did it go extinct in Hong Kong in the first place?

a Maxima clam tucked into some hard coral (via WikiCommons)
a Maxima clam tucked into some hard coral (via WikiCommons)
What happened to the Maxima clam in Hong Kong?

Apart from the fact that the Maxima clam lived on coral reefs in Hong Kong waters, I can not find any more details of how big the population was, which exact areas in inhabited (obviously coral reefs, so that narrows it to Eastern and Southern Hong Kong waters) or whether it was harvested locally. It is however clear that Hong Kong used to be a big regional market for giant clam species in Asia. Giant clams were and still are a delicacy in Asia (mostly the meat big abductor muscle) and the shell was used for decoration (though not extensively). Even the UN Food and Agriculture Organization has no useful fisheries statistics for Tridacnids. So there is no information on how many – if any – were harvested from Hong Kong waters before they disappeared.  The maxima clam like all clams is a filter feeder which suck in water, filters out and swallows edible particles and then ejects the water out again. As such it is quite vulnerable to toxic substances in the water. In addition, it harbors symbiotic microscopic algae called zooxanthellae (zoo-oh-zan-the-lay) in its tissue. These absorb the clams waste  products like CO2 and photosynthesize turning them into sugars in the presence of sunlight and giving off oxygen for the clam.

When open, the bright blue, green or brown mantle of the clam is exposed and obscures the edges of the shell which have prominent distinctive furrows. The attractive colours of the mantle are the result of pigment cells, with a crystalline structure inside. These are thought to protect the clam from the effects of intense sunlight, or to bundle light to enhance photosynthesis of the zooxanthellae.


Maxima clams – one open showing the brightly colored mantle, the other closed and only identified by the zig-zag pattern of the shell valves. (via WikiCommons)

This is essentially what corals do, too, which is why they share the same habitat – coral reefs. And like most reef corals the maxima clam also gets most of its nutrients from its zooxanthellae . Coral reefs suffer enormous damage from smothering by sediment that washes into the sea from rivers and rainfall and from clouding of the water and smothering by excessive algal blooms. Both of these were and still are to some extent big problems for Hong Kong waters, whereas in the past this was not the case. Algal blooms and sediment runoff increased a lot as a result of the increase in human population in Hong Kong and as a result of rapid industrialization and the associated water pollution. This combined with harvesting seems to be the most likely reason for the disappearance of the Maxima clam from Hong Kong waters before 1983.

Will there ever be giant clams in Hong Kong again?

I hope so. Like I said earlier, if conditions are right, any of the wide-ranging planktonic larvae of the clam that stray into Hong Kong waters could settle and grow to adulthood. Failing that humans could also try to establish them by attaching cultured juveniles to appropriate spots on reefs – but this is more complicated and costly, although Singapore has attempted this with initial success using another giant clam species Tridacna squamosa. But the main criteria is suitable conditions for a population to establish and grow – in other words we need clean seas again. Hong Kong has improved a lot on this front up until very recently, when the increased coastal development in southern China started to create a lot of water pollution which somewhat diminishes the results. There is still a long way to go. But I would say that divers should keep an eye out. In fact, the ReefCheck 2015 recorder forms even have a section for giant clams (Tridacna sp.), so its not just me that is hopeful! You never know. you could be diving some coral reef in Sai Kung, Tung Ping Chau, Hoi Ha Wan or the Ninepin Islands and come across a maxima clam. It might be an old dead one stuck in a reef with just the wavy outline of the two shell valves (probably) or it could have the fat, bright blue or green mantle of a live clam – in which case 1) hooray for Hong Kong and 2) please report your finding to the AFCD and Reef Check!

24th of June 1957 – 11-foot Manta Ray Caught Off Big Wave Bay

History and nature appreciation don’t normally go hand in hand, but they should, because unless you know what used to live in Hong Kong waters, you don’t know what constitutes ‘good condition’ of the marine environment. So I love looking through old papers and spotting the ‘monsters’ of long ago.

And here is one the China Mail reported on its front page on 24th of June 1957:


Chinese fisherman caught a 11-foot (3.35 m) Manta ray at Big Wave Bay yesterday afternoon. This was reported this morning by a Colony resident, Mr A S Dower. Mr Dower said there were two junks lying off the beach an it appeared that the Manta was caught from one of these. At about 7.15 p.m. , as the beach began to clear, the fisherman rowed a sampan to shore towing the ray behind. Then they beached the ray. Mr Dower said that when he left soon after it was still there. The catching of the ray was the climax of an exciting afternoon. The shark bell sounded four or five times. “It seemed to be dinging all afternoon”, one swimmer said. “I am not sure they were all sharks. I saw a fin once a good way out but I’m not sure it was a shark or a Manta.The Manta has a small fin – I noticed it when it was brought to shore,” he said. Big Wave Bay was crowded yesterday afternoon. Two rows of tents lined the beach and during the afternoon they were fully occupied. But the surf was flat. A porpoise was also reported to have been caught at Big Wave Bay last night.

So, 3.35 m wide Manta rays and porpoises at Big Wave Bay in 1957. We still have the finless porpoise (Neophocaena phocaenoides) in HK, but I have never heard of anyone seeing or catching a Manta ray in my living memory. Nur according to other sources villagers in eastern waters caught manta rays in the 1960’s using the oil from the liver to light lamps and the gills as medicine. Manta rays are oceanic species and not really costal dwellers, so I suspect they would only pass through HK much like great whales, tuna and many shark in the summer months. According to the Agriculture, Fisheries and Conservation Department the species Manta birostris has been reported from HK waters and they can grow up to 8 m in width!

It’s my hope that someday some HK diver is going to post an amazing video online – like the one below from Bali (WikiCommons)- of Manta rays swimming through Hong Kong waters. And this is not an unrealistic hope either! The Thames river and estuary was delcared ‘biologically extinct’ in the 50’s but recovered following environmental protection legislation and efforts to rehabilitate it, and now it has dolphins, salmon, seals and even the occasional whale…right up to central London. And similar things have happened in other formerly polluted waterways near major cities. As long as we don’t cause species to go extinct (in the case of Mantas by eating too much of their gills and killing them as bycatch etc), there is always hope they will someday come back.

Sea Spiders, Chinese Takeaways and Taxonomical Humor

Sea spiders? Sounds like a B-movie horror story: ‘Sharkrantula”, maybe? Not at all. Sea spiders is the common name for pycnogonids (pik-noh-go-nids) which are a type of marine arthropod (joint-legged animal) which includes crustaceans like crabs, lobsters, shrimp and prawns, but also insects. But pycnos have actually got more in common with horseshoe crabs and spiders in terms of anatomy, so the name sea spiders is not too far from the truth.

Calipallenid pycnogonid via Flickr
Pycnogonid can be beautifully colorful

The occur in seas all over the world from tropical reefs to frozen polar seas and from shallow water to depths of over 7,000 m. Most are tiny although some deep-sea species can grow to 90 cm. Pycnogonids have extremely reduced bodies in which the abdomen has almost disappeared, while the legs are long and clawed. Muscles are in some cases reduced to a single cell! They can even breathe and absorb food through their skin. As you can imagine their dietary needs are therefore very small. And yet they are predators that prey on corals and worms. The head has a long proboscis with an unusual mouth at the end and several simple eyes on a tube-like stalk. The head also has a pair of claws and a pair of attachments on which the eggs can be carried. All in all, it can be very hard to tell just which end of a pycnogonid is the head!

You might think so what? Spiders are creepy and yucky and iffy. But marine biologists love pycnos – they are just so strange and fascinating biologically.

Two pycnos mating. You could be forgiven for thinking it was just one. Now tell me which end is the head???

But what has all this got to do with Chinese takeaways And taxonomical jokes?

Earlier this year I received the sad news that the head of the department I used to work in the Natural History Museum in London passed away. Roger Bamber (tribute by Dr. Tammy Horton) was a legend of a man and also an expert on pycnogonids – a pycnogonid taxonomist. Unlike the more familiar taxidermist (who stuffs and preserves dead animals), a taxonomist is an expert on the certain groups of animals or plants and decides what is and is not a new species – but come to think of it and they also work with dead animals and need to preserve them…sometimes they stuff them too…but its much more complex and tricky, I promise. There is a difference honestly!

Anyway, one of Hong Kong’s pycnos (there at least 6 species locally) was discovered by Roger. Tanystylum sinoabductus was identified in Hong Kong’s only marine reserve at Cape D’Aguilar where the Swire Institute of Marine Science is located. (Note: a marine reserve, unlike a marine park, does not allow any sort of anchorage or fishing, so its is completely protected – except for water pollution of course.) This particular pycno was found in exposed mussel beds. But at only roughly 1/2 a mm in size you will only see it with a magnifying glass and only recognize it under a microscope.

And now the for long awaited joke: the species is part of the genus Tanystylum, but the specific (species) name that Roger chose – sinoabductus -is the taxonomical joke. Sino in latin means chinese (duh!), and abductus – if you have not already guessed it – means ‘taken away’, thus sinoabductus is the “Chinese takeaway’. OMG, I hear you say. What an unfunny joke! You have to understand there is not much opportunity for humor in science (except in the pub after the work) and marine biologists spend a long time in the lab staring down a microscope or hours pouring data on a computer and reading and writing scientific papers any chance to get away with even a bit of humor is appreciated!
A typical chinese takeaway restaurant in the UK – and also the inspiration for the name of a pycnogonid sea spider…taxonomical humor.

And just in case anybody in this era of social justice warriors and political correctness thinks that this species name could be racist: the other reason for the name is that the type species – that is the 1 animal that was selected as typical of the species and which represents the ‘gold standard’ for that species – now resides in the National Museum of Wales in Cardiff, UK. Thus this Chinese sea spider species was in fact ‘taken away’ to a noted museum for that group of animal (which is standard practice as well, so no accusations of kidnapping or robbery please!).

Never ask a pycnogonid taxonomist for a Chinese takeaway. Bon appetite!

Painted Sweetlips and quiz!

A good post from fellow HK undersea blogger ‘green blue sea’ about the lovely sweet lips fish of HK.

green blue sea ∙ 蔚藍碧海

A strong contender for the ‘fish with the sexiest name’ award, the sweetlips are a big family of around 140 species, many of which are very pretty. If you’ve ever dived much in tropical reefs you will probably recognise these fairly large and unmistakeable spotted or stripey fish. They do indeed have big lips, and big doe eyes as well, giving them a bit of a dopey look. Here are some I spotted in the Philippines:

Left: Lined Sweetlips at Tubbataha Reefs; Right: Ribbon Sweetlips at Kerikite Island (and spot the odd one out — it’s a Painted Sweetlips)

In Hong Kong waters we have a few resident species of sweetlips. They are shyer and less flashy than the tropical species and a 2013 fish survey concluded that three out of the four local species they recorded were either ‘uncommon’ or ‘rare’. The one common species which local divers are most likely to…

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