Why the uncommon Sailfin roughshark is graced with the scientific name Oxynotus paradoxus may only be known to monsieur Frade who has been founded this name in 1929. I don’t know why this species of roughsharks should be sorted into the category of paradoxical biological species.
Like all roughsharks, the Sailfin roughshark has got rough skin with large denticles, looks like a fleet of sailboats, lives in the deep sea (at depths between 869 and 2,362 ft – 265 and 720 m -) and is ovoviviparous. The pups are born at 9.8 in – 25 cm – length and grow up to at most 3.9 ft – 1.2 m – long.
Living in the eastern North-Atlantic from Scotland to Senegal, the Sailfin roughshark, like all deepwater species, is a (albeit rare) bycatch of offshore trawling fleets. Since it is poorly known, the IUCN considers its status as data deficient.
Sharks of the family sleeper sharks are bad ass: they like it cold (like the Greenland shark) as well as hot (like the Pacific sleeper shark). But one of them also likes it deep: the Portuguese Shark (Centroscymnus coelolepis) is the record holder for greatest depth attained by any shark. It usually inhabits depths below 1,300 ft -400 m-, but has been caught as deep as 12,057 ft -3,675 m. It is special in other aspects, too. It has very large dermal denticles shaped like scales of bony fish, and its eyes are well adapted to deep sea conditions: large and green due to a reflective layer named tapetum lucidum (like cat eyes), its cells are optimized for detecting movement and bioluminescence.
The Portuguese shark can be found worldwide, but patchily, in several distinct population in the Atlantic and Mediterranean Sea, Pacific and Indian Ocean. It is on average 3.3 ft – 1.0 m – long and ovoviviparous with an average number of 12 pups after one year of gestation (due to the vast extend of the deep sea, it seems that copulation trigger ovulation).
There is depth segregation by size and sex; since pregnant females are found in shallower water of the deep sea, they are more at risk by fishing pressure. It is targeted for the squalene in its liver (22 to 49% by weight) and its meat, but mostly taken as bycatch by bottom trawlers. Thus the IUCN considers the Portuguese shark as Near Threatened and even Endangered in European waters, despite a zero Total Allowable Catch since 2010, because even if discarded, as deep sea species the survival rate is likely to be low. It seems that a separate sub-population in the Mediterranean Sea is secure because it occurs at depths that are outside of the scope of existing fisheries, additionally there has been a ban on deepwater fisheries operations below depths of 3,300 ft – 1,000 m – since 2005.
Like its sister species, the Necklace carpetshark, the Ginger carpetshark or Sparsely spotted carpetshark (parascyllium sparsimaculatum) lives solely off Australia. But, unlike every other species of the family collared carpet sharks, it is a deep sea species. Its depth range seems to be 669 to 804 ft – 204 to 245 m. It was first described in 2002 and only known from 3 specimens, all found in an extreme small range off western Australia.
It is assumed that the Ginger carpet shark is, like all other collared carpet sharks, oviparous (that means female sharks lay eggs).
After introducing dangerous sharks, here a harmless one.
But hold on! The teeth look dangerous, doesn’t they? But this rare, medium sized shark is indeed considered harmless (not that little means automatically harmless, look at the cookiecutter shark), despite its name: knifetooth dogfish.
The knifetooth dogfish (Scymnodon ringens) lives in the deep sea in the Eastern Atlantic and Southwest Pacific and is up to 3.6 ft – 1.1 m – long. It looks, with the exception of its teeth, like a relative of the pocket shark or the ninja lanternshark, but it is actually a species of sleeper sharks (like the Greenland shark). It is used for dried or salted meat and fishmeal.
Teeth must be really something distinctive, since there is a sleeper shark called sparsetooth dogfish, too.
Did you know that the skin of the seal shark (Dalatias licha) has been made into an expensive leather called shagreen and used in Europe for book binding, sword hilts, luggage and jewelry since the 17th century?
The skin is dark brown (that’s why the seal shark is called Schokoladenhai -schokolade shark- in German) with small and flat dermal denticles. Reaching usually 4.6 ft -1.4 m – in length, the seal shark is with its large teeth and strong bite a powerful predator, but can also take bites out of larger prey, just like its little cousin, the cookiecutter shark (although its lips are not modified to be suctorial).
Like all sharks of the family kitefin sharks, the seal shark is a deep sea shark with a slow growth and small reproductive rates. Females give birth to 6 – 8 living young after a gestation period of two years. The embryos hatch inside one of the two functional uteruses (not divided into compartments) and are sustained by yolk (ovovivipary). In between pregnancies the females may have a year of rest. The young are born at a length of 12 to 18 in -30 to 45 cm- and mature at 2.53 to 3.97 ft – 77 to 121 cm- (males) and 3.84 to 5.22 ft – 117 to 159 cm – (females).
The seal shark (also known as kitefin shark) is caught commercially for its liver oil (especially its squalene) and skin (see above) as well as for meat (in Europe and Japan, but also Australia due to the relaxation of regulations regarding seafood mercury content) and fish meal, but also as bycatch in deepwater longline, bottom trawl and gillnet fisheries. Once discarded overboard, deepwater sharks rarely survive. This causes the seal shark to be considered Near Threatened globally and Endangered in European waters. Due to its habitat near the bottom of the sea the seal shark is no danger to humans, but bites occasionally into underwater fiberoptic cables.
The classification of shark species can be difficult. Sometimes juvenile and adult specimen of one species are considered different species (Zebra Shark). And sometimes a species is considered equal to another (the sister species birdbeak shark), but the same species found in another place (off Madeira) get its own name, until 3 years later both are deemed the same, new species – the rough longnose dogfish (Deania hystricosa).
The rough longnose dogfish is a medium sized (up to 43 in -110 cm- long) deep sea shark and has been found in the Eastern central and southeast Atlantic around Madeira, the Canary Islands, Namibia and South Africa and the Northwest Pacific around Japan and New Zealand (so far). The species belongs to the family gulper sharks and has got grooved spines in front of both dorsal fins and rough, pitchfork-shaped dermal denticles. It is ovoviviparous with probably around 12 pups per litter. It is taken by deepwater longline fisheries off Madeira and the Canary Islands for its meat and liver oil and as bycatch by bottom trawl fisheries elsewhere.
Did you know that a little deep sea shark (classified as “Vulnerable”) is – due to the big portion of high-quality squalene in its liver oil – considered as “the Rolls-Royce of squalene-producing sharks” and targeted purposefully (whether legal or illegal doesn’t seem to matter)? Beside the here mentioned use of squalene in expencive cosmetics and dubious health capsules -where other squalene sources could easily be used instead – is it a (according to GSK without alternative) ingredient to medical products, too, like the flu vaccine adjuvant AS03. I don’t want to discuss the whole purpose of vaccines, or adjuvants, or the in Europe highly controversial pig flu vaccine of 2009, either – but it is to lament that many Gulper sharks (Centrophorus granulosus) were sacrificed pointlessly, since millions of swiftly produced and paid vaccine doses had to be destroyed later. And that in the case of a shark with the probably lowest reproductive rate of all sharks.
Female gulper sharks reach maturity at 14 and can live between 54 and 70 years long. Since they are pregnant with only one pup for 2 years and take long breaks in between, they typically have only between 2 and 10 pups in their lifetime. They are ovoviviparous and feed the embryo with yolk and unfertilised and also fertilised eggs (oophagy). The egg cell of the gulper shark reaches one of the largest cellular sizes described for any animal, weighing between 143 and 370 grams.
Living in the Atlantic, Pacific and Indian Oceans as well as the Mediterranean Sea, the Gulper shark is caught on longlines and by trawling (together with various other marine animals as bycatch). It is a highly migrating species and forms schools.
Like other sharks of the family gulper sharks (Centrophoridae), the Longsnout dogshark is a deepwater shark and ovoviviparous. It has got a extremely long snout (hence the name), and lives in the Atlantic and Indian Oceans and in the South Pacific at depths between 490 and 4460 ft -150 and 1360 m- (but usually between 1310 and 2690 ft -400 and 820 m). Since it only grows to about 45 in -115 cm – it is a rather little shark.
Did you know that there is a shark named Dorian Grey? The Deania calcea has got other strange names, too: Birdbeak dogfish, Platypus Shark, Shovelnose Spiny Dogfish and Brier Shark. Some of them I can understand, but others not.
Do they mean the literary character Dorian Gray (with an a instead of an e)? I hope they don’t compare his picture to the image of this shark – what I know of the story indicates that it looked much more gruesome than this little shark. Its face looks a little like the head of a platypus or the beak of a bird, maybe a shovel, but a thicket (brier)?
Names aside, the birdbeak dogfish is a deep water dogfish living in the Pacific Ocean around Japan, southern Australia, New Zealand, and Chile, and in the Atlantic Ocean from Iceland south to the Cape of Good Hope. It has got a very long, narrow snout and pitchfork-like denticles.
Maturing at 17 years (males) and 25 years (females), it has a longevity of about 35 years and reaches up to 48 in -122 cm- length. The female is ovoviviparous with up to 12 pups per litter.
Usually a mid-slope shark (at depths between 239 ft and 4757 ft -73 and 1,450 m-) on the outer continental and insular shelves, birdbeak dogfish seems to migrate vertically and can be found on the upper slopes, too. Since its liver is high in squalene (about 70% by weight), it is targeted for its liver oil and flesh. Catches in Australia have been increasing in the last few years with relaxation of mercury laws and fishers turning to non-quota species. In 2002 regulations in the South East Trawl fishery in Australia prohibit the landings of livers of all sharks unless the accompanying carcass is also landed.
In the family of lantern sharks there are many little-known sharks (the deep sea holds many secrets). One of them is the Bareskin dogfish or Jelly shark (Centroscyllium kamoharai).
This shark species was first named in 1966 and has been found rarely since then. Living in a depth range of 1,600 ft to 4,000 ft -500 m to 1.2 km- in the western Pacific, it is a small shark: mature at 15 in – 40 cm- and a maximum length of 23 in -60 cm. The IUCN considers the Jelly shark like other deepwater dogfishes as highly vulnerable to bycatch, but doesn’t has enough data yet. Since in the meantime monster boats are catching indiscriminately giant amounts of deepwater fish for fish meal every day, there is a risk that enough data may come to late.
The one distinct feature of the Bareskin dogfish are its sparse denticles. I don’t want to expose you to the few images of this shark I found (trust me), so I post an image of normally denticled shark skin instead. This shark doesn’t seem to need that, maybe because it doesn’t swim fast.