Even now, the vast oceans hold many secrets. The Harlequin Catshark (Ctenacis fehlmanni) is a really poorly-known species of finback catsharks (Proscyllidae or false catsharks). Only few specimen have been found, the first (holotype) around 1960 off Somalia.
The only 18 in -46 cm- long female shark held one thin-walled, large egg-case in each uterus, but experts don’t agree upon if this species is ovoviviparous (that means the young hatch out of these egg cases inside their mother and are born alive) or oviparous (lay egg cases). The family Proscyllidae consists of species with both modes of reproduction.
Since no deep-sea trawling fisheries take place off Somalia, this deep-sea species is considered “Least concern”.
Many shark species are victims of increasing fishing pressure, even if they are not targeted themselves: as bycatch. That is a big problem if they are endemic to only a small range or show only a low fecundity – the African ribbontail catshark (Eridacnis sinuans) is both.
Living solely in deep waters off Mozambique (and between this island and the coasts of South Africa and Tanzania), fortunately only part of its range is subject to intensive bottom trawl fisheries. At least for now.
Sharks of the family Proscylliidae, also called false catsharks, look a lot like catsharks, but their first dorsal fin starts as soon as their pectoral fins end.
Being not quite as small as its sister species, the pygmy ribbontail catshark, female African ribbontail catsharks of about 14 in – 35 cm – length give birth to 2 (one from each uterus), between 6 and 6.7 in – 15 and 17 cm – long living pups (ovoviviparous).
As mentioned last week, the Broadfin shark had been categorized as Endangered by the IUCN. But this happened before its sister species, the Borneo Broadfin shark (Lamiopsis tephrodes), has been again considered as separate species due to biomolecular analyses. Discovered in 1905 (instead of 1839, where he wasn’t even alive) by zoologist Henry Fowler, it had soon been equalized with the Broadfin shark.
Reaching only 4.3 ft – 1.30 m -, the Borneo Broadfin shark lives solely off Borneo. Due to fishing pressure in this waters and 2 separate species, the IUCN should maybe revise its classification.
Another species of requiem sharks is the Broadfin shark (Lamiopsis temminckii). Living solely in shallow waters off India, China and Southeast Asia, it suffers greatly from habitat destruction, overfishing and water pollution. The IUCN considers this species as endangered.
Like almost all other requiem sharks, the Broadfin shark is viviparous. 4 to 8 embryos feed at first from yolk and later via a placental connection. After about 8 month they are born at 15 to 23 in -40 to 60 cm- length. Maximal length is 5.5 ft – 1.7 m.
Here the third shark of the triplet: the Blackspot shark (Carcharhinus sealei). Often confused with the whitecheek shark and until 2012 equated with Coates’s shark, it is also a rather small requiem shark, reaching a maximal length of 37 in -95 cm. After a gestation of about 9 month, only one or two pups of 13 to 17 in – 33 to 45 cm – length are born alive (viviparous).
The Blackspot sharks is even more widespread as the Whitecheek shark and not only inhabits shallow waters off northern and western Australia, but coastal waters all over the Indo-Pacific Ocean from South Africa and Madagascar over India to Indonesia. Despite living in intensively fished waters and often caught for its meat, it is only considered Near Threatened by the IUCN. If there where enough data, it may be very well meet the criteria of Vulnerable.
The classification of sharks is difficult. That’s true in particular for the species of requiem sharks that all looks quite alike. The Coates’s shark (Carcharhinus coatesi), named after the ichthyologist George Coates, was discovered in 1939, but had been equated with the Blackspot shark (Carcharhinus sealei) since 1982. As recently as 2012 they have been adjudged as 2 different species, after all.
The Whitecheek shark (Carcharhinus dussumieri) is a different species, too, but is synonymous with Coates’s shark in the source of my picture, that’s why it could be false.
The Coates’s shark is a small shark. Born alive (viviparous) at a length of 15 to 16 in – 38 to 40 cm -, it grows to at most 2.89 ft – 88 cm. It inhabits the surface to a depth of 404 ft – 123 m – off northern Australia.
One of many shark species in Australian waters is the Creek whaler (Carcharhinus fitzroyensis). Inhabiting shallow waters off northern Australia, it can also be found in estuaries (first in the Fitzroy river estuary, thus the scientific name). Like almost all requiem sharks female Creek whaler are viviparous, that means the depleted yolk sac changes into a placental connection. Every year, up to 7 pups are born in special nursery areas. Newborns are between 14 and 20 in -between 35 and 50 cm- long and grow up to about 4.3 ft – 1.3 m.
Creek whaler pose no danger to humans and are only a minor part of shark catches off Australia (as bycatch). The IUCN considers them as least concern (but this classification from 2003 may be now in need of updating).
In 2013, after genetic analysis on 54 young sharks found off South Carolina (in the U. S.), a new species of hammerhead sharks has been established: the Carolina hammerhead shark (Sphyrna gilberti).
There are very few pictures of this new species, but it seems to look like a little Scalloped hammerhead. At least, the examinated pups had been smaller than ones from the Scalloped hammerhead.
Another difference is that it has got 10 fewer vertebrae than a typical scalloped hammerhead, a fact that has been noted as early as 1967 by Ichthyologist Carter R. Gilbert. Though he considered it an anormal scalloped hammerhead, it already could have been very well a specimen oft this new species. That’s why it is now named after him.
Did you know that hammerhead sharks did not gradually develop such a large hammer, as it had been believed for decades? Genetic tests showed the opposite. Sharks with giant cephalofoil (hammer) like the Winghead shark, where it is as wide as up to 50% of the shark’s total length, are the primary species, from with later evolved species with a smaller hammer. The benefits of the hammer have to exceed the hindrance of its deformity by far.
The Winghead shark (Eusphyra blochii) forms its own genus within the family hammerhead sharks and has been named after the German naturalist Marcus Elieser Bloch, who described it for the first time in 1785. It is a slender shark (hence the additional name Slender hammerhead shark) and has got not only particularly protruding hammer wings (which are at birth folded back along the body and unfold only later on) but extremely long nostrils, too. After a gestation period of 8 to 11 months, where approximately 11 embryos have got each their own compartment inside the uterus and are nourished by yolk and later by a placental connection (viviparous), they are born at a length of 13 to 19 in – 32 to 47 cm. They are slow growing and reach up to 6.2 ft – 1.9 m – at length and 21 years of age.
The Winghead shark lives in coastal tropical waters of the Indio-West Pacific. Due to the high fishing pressure for its fins and meat and the degradation of its habitat in these areas, the IUCN has been classified it as endangered since 2016 (prior to that it was only considered near threatened, but it is absent from several areas by now).
Sharks do have special healing abilities. They often get wounds (due to mating rituals, combat, collisions with reef substrate or fishing gear) which, however, heal remarkably quickly. A part in it is the fact that dermal-denticles are teeth and are continually replaced like real teeth. Thus wounds are quickly covered with temporary, larger denticles, and the resulting scar become invisible by normal shaped denticles within 6 month.
An example of this was found in Scalloped hammerhead sharks (Sphyrna lewini). This species of Hammerhead sharks (also known as bronze, kidney-headed, or southern hammerhead sharks) lives all over the world offshore in warm and tropical waters near the surface, partly in large schools. This and the fact that there are several distinct sub-populations makes this species highly susceptible to fishing pressure. They are caught commercially for their meat and skin, but manly their fins, often illegally (IUU), as bycatch or as big game fish by recreational fishermen. That’s why they are worldwide considered endangered by the IUCN.
Scalloped hammerheads are up to 14 ft – 4.3 m – long (but on average only up to 8.2 ft – 2.5 m – as female and 5.9 ft – 1.8 m – as male). They are viviparous (once the yolk sack is depleted it converts into a placental connection) and give birth after 9 to 12 month in specific, shallow nursery areas to up to 40 living young. The pups grow slowly and often fall prey to larger sharks, what explains the relative large litter size.