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).
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).
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.
My first shark of the week in 2018 is the Prickly dogfish.
First discovered as a cadaver on a beach on Bruny Island off southeastern Tasmania, hence the name Oxynotus bruniensis, this species of the family Roughsharks can be found over the outer continental or insular shelf in southern Australia and throughout New Zealand.
With a prominent “humpback” and extremely rough skin, the Prickly dogfish looks a little different than other Roughsharks, but the shape and the “sailfins” can not be mistaken for something else. It is ovoviviparous with around 7 pups being born at 9.4 in – 24 cm – long. It reaches up to 30 in – 75 cm – in length.
Living in a typical depth range of between 1,150 and 2,130 ft – 350 and 650 m -, the Prickly dogfish is prone to be caught as bycatch by trawlers.
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.
The Prickly shark (Echinorhinus cookei), looking like the big brother of the Ninja lanternshark, is thankfully not as irritable as its name suggests. On the contrary, despite its size of up to 13.1 ft -4 m- it is rather shy around humans.
The Prickly shark, as well as its brother Echinorhinus brucus from the family Bramble sharks or Echinorhinidae, is known for its thorn-like denticles. Thus its scientific name Echinorhinus, which is greek for echinos = hedgehog or sea urchin and rhinos = nose. It inhabits deeper coastal waters of the Pacific ocean from California and Hawaii to Chile and China to New Zealand and stays as a homebody in a rather small home range of 0.85 sq mi -2.2 km2. It likes it rather cool and stays by day in depths of up to 4900 ft -1500 m-, but migrates at night upwards near the surface.
Prickly sharks are not targeted directly (its meat isn’t tasty), but are often victims of bycatch of deepwater trawl fisheries to sate our increasing need for fish meal (used for aquaculture and pig, chicken and even cow husbandry). Therefore they are considered as near threatened by the IUCN, even though a female has been found with up to 114 embryos (they are ovoviviparous).
The Shorttail nurse shark (Pseudoginglymostoma brevicaudatum) has got a very long scientific name. This is due to the fact, that, since 1986, it hasn’t been sorted into the genus Ginglymostoma like Pacific nurse shark and Nurse shark but has been named as false (pseudo-) nurse shark.
As the name implies, this nurse shark has got an extreme short tail. It is also the smallest shark of its family with up to 2.46 ft – 75 cm – length. Unlike the Tawny nurse shark, who is in fact ovoviparous, but whose egg cases pile up in captivity and are unfertilized ejected, the Shorttail nurse shark lays indeed eggs (oviparous), out of which after around 5 month young hatch, proven by the successful breeding in Amsterdam’s zoo since 2006.
Living on coral reefs off east-Africa and Madagascar in distinct sub-populations, the Shorttail nurse shark is considered “vulnerable” due to high fishing pressure (it is taken as bycatch and for its fins, meat and skin) and habitat destruction. It has been caught for aquaria, too, which could be supplied now as well from breeding programmes.
Did you know that there are sharks with chameleon traits? They are able, to a certain degree, to change their color to hide. One of them (even if it is not observable in this viedeo) is the Collared carpetshark (Parascyllium collare), namesake of its entire family.
Just like last weeks Ginger carpetshark, the Collared carpetshark lives off Australia, more precisely in depths of 180 to 420 ft – 55 to 128 m – near the floor of rocky reefs on the continental shelf off eastern Australia. It is common, but only poorly known. Its maximum length is only 2.79 ft – 85 cm- and females are oviparous.
Collared carpetsharks are not targeted, but often taken as bycatch since they reside in some areas of heavy trawling effort. Then they are mostly discarded (if not, they are later used as bait) and survive this, therefore they are considered least concern. They also benefit from areas with few fishing pressure.
Another example to prove the Plate tectonics, anyone? Well, the Smalltail shark (Carcharhinus porosus – named after really big pores behind its eyes) was considered, until 2011, to live in coastal waters on both sides of the Isthmus of Panama: in the western Atlantic Ocean from the northern Gulf of Mexico to southern Brazil as well as in the eastern Pacific from from the Gulf of California south to Peru. A momentous mistake that seems to continue until now (see IUCN Red list and homepage of the Florida Museum). In fact, its sister species Pacific smalltail shark (Carcharhinus cerdale) can be found in the eastern Pacific, and the Smalltail shark lives only in the western Atlantic part. Both had been separated around 2.8 million years ago and developed into different species (just like the Whitenose shark and the Blacknose shark a proof of evolution, as well).
This small (generally only up to 3.6 ft -1.1 m- long) requiem shark is slow growing and viviparous with two to nine young every two years after an approximately 12-month gestation period. It can be found near the bottom of coastal waters and estuaries and forms large aggregations segregated by sex.
Along the northern Brazilian coast, where some of its nursery areas are, the Smalltail shark is the most common shark, and in Trinidad the most economically important shark (under the name puppy shark). Fishing pressure as bycatch as well as targeted (for its meat, fins, cartilage and liver oil) caused a significant decline in numbers, resulting in an ICUN-classification as vulnerable in Brazil, where mostly juveniles have been caught, but only data deficient overall. Since its habitat is much more narrow as previously assumed (see above), the IUCN should revise that urgently (in my opinion).