save our blue planet

Let's save our blue planet by saving the ocean. Every little step counts.

Shark of the week: Winghead shark — 15. January 2018

Shark of the week: Winghead shark

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.

Eusphyra blochii X-ray.jpg
X-ray of Eusphyra blochii by Sandra Raredon/Smithsonian Institution –, Public Domain, Link

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 (ovoviviparous), 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).

Sources: here and here

Shark of the week: Scalloped hammerhead — 8. January 2018

Shark of the week: Scalloped hammerhead

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.

Hammerhead shark, Cocos Island, Costa Rica.jpg
Scalloped hammerhead by Barry PetersFlickr, CC BY 2.0, Link

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 ovoviviparous (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.

Sources: here, here and here

Shark of the week: Prickly dogfish — 1. January 2018

Shark of the week: Prickly dogfish

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.

Oxynotus bruniensis.jpg
A prickly dogfish (Oxynotus bruniensis) at the Rumble V submarine volcano (cropped version of original to focus more on the fish) by New Zealand-American Submarine Ring of Fire 2005 Exploration, NOAA Vents Program –, Gemeinfrei, Link

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.

Sources: here and here

Shark of the week: Sailfin roughshark — 25. December 2017

Shark of the week: Sailfin roughshark

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.

Oxynotus paradoxus.jpg
Oxynotus paradoxus by © Citron / , CC BY-SA 3.0, Link

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.

Sources: here and here

Shark of the week: Portuguese shark — 18. December 2017

Shark of the week: Portuguese shark

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.

A small, dark brown, heavy-bodied shark with large green eyes and small fins, lying on the ground next to a meterstick
Centroscymnus coelolepis by Jon Moore – Marine Fisheries Review 65(4), Public Domain, Link

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.

Sources: here, here and here How to talk to someone who doesn’t believe in climate change | Wie mit jemandem reden, der nicht an den Klimawandel glaubt — 16. December 2017 How to talk to someone who doesn’t believe in climate change | Wie mit jemandem reden, der nicht an den Klimawandel glaubt

Not every conversation with a climate denier has to lead to raised voices and hurt feelings. Here’s how to do it constructively. “Climate change has become one of the taboo topics — like sex, politics and religion — that doesn’t get talked about at the Thanksgiving table,” says Anthony Leiserowitz, director of the Yale Program…

Via How to talk to someone who doesn’t believe in climate change —

Shark of the week: Prickly shark — 11. December 2017

Shark of the week: Prickly shark

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.

Echinorhinus cookei head2
head of Echinorhinus cookei by D Ross Robertson [Public domain], via Wikimedia Commons
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).

Sources: here, here and here

Shark of the week: Shorttail nurse shark — 4. December 2017

Shark of the week: Shorttail nurse shark

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.

egg-case Pseudoginglymostoma brevicaudatum
Egg capsule of Pseudoginglymostoma brevicaudatum, © Chris Avila, Toronto Bentic Sharks, Canadian Marine Aquaculture, Toronto

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.

Sources:hereherehere and here

Shark of the week: Tawny nurse shark — 27. November 2017

Shark of the week: Tawny nurse shark

The Tawny nurse shark (Nebrius ferrugineus) is a docile shark of the family nurse sharks and lives in the Indian Ocean from the Red Sea to South Africa and India and in the western Pacific from Australia and Japan to South Sea islands. It inhabits shallow coastal waters in depths up to 230 ft – 70 m – on coral reefs. It is nocturnal and feeds from small fishes, corals, sea urchins, sea snakes, crustaceans and especially octopuses, which it sucks into its small mouth.

The female Tawny nurse shark is ovoviviparous. The embryos feed (after depleting their yolk sack) from big eggs (oophagy), they compete for food and maybe prey on weaker siblings (cannibalism) – in any case mostly only one out of 4 embryos per uterus survives. The pups are born at 16 to 31 in -40 to 80 cm- and grow up to 10 ft – 3.20 m- length. They mature at 8 ft 2 in – 250 cm – (males) and 7 ft 7 in to 9 ft 6 in – 230 to 290 cm – (females) and loose their spots on the white belly. Their color is yellowish brown (since their name).

Even if Tawny nurse sharks are mostly gentle and can be trained (it is said that on some South Sea islands children even ride them), they get wild and spit, grunt and bite when provoked or captured. That’s why they are targeted by recreational fishermen as big game fish. Except in Australia they are fished commercially for their meat, fins, skin and liver oil (partly using explosives or poisons) and caught for aquariums. Additionally they are harassed by divers and their habitat gets often destroyed. Therefore they are considered vulnerable worldwide by the IUCN.

Sources: here, here and here

shark of the week: Collared Carpetshark — 20. November 2017

shark of the week: Collared Carpetshark

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.

Sources:herehere and here