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Hai der Woche: Schwarzspitzen-Riffhai — 16. October 2017

Hai der Woche: Schwarzspitzen-Riffhai

Der Schwarzspitzen-Riffhai (Carcharhinus melanopterus – abgeleitet von melas = schwarz und pteron = Flügel oder Flosse (siehe Pterosaurier)) ist ein weiterer Requiemhai, der in Korallenriffen lebt. Er bewohnt küstennahe Gewässer des tropischen und subtropischen Indo-Pazifik von Südafrika bis Hawaii (hat sogar das östliche Mittelmeer durch den menschengemachten Suez-Kanal besiedelt) und bevorzugt seichtere Gewässer als seine Kollegen Grauer Riffhai und Weißspitzen-Riffhai. Ihre Kinderstuben (die Weibchen sind vivipar und bringen lebende Junge zu Welt, nachdem sie diese mit Dotter und über eine Plazenta-Verbindung ernährt haben) können so flach sein, dass die Jungen mit ihrer Rückenflosse aus dem Wasser ragend schwimmen müssen und aussehen “wie eine Flotte von Mini-Segelbooten” (Zitat von hier).

An expanse of clear water and white sand, and several sharks swimming with their black-tipped dorsal fins protruding above the water
Carcharhinus melanopterus by Leon Brocard from London, UK – PIMG_2915, CC BY 2.0, Link

Nicht nur Junge bevorzugen es, aus Schutzgründen in Gruppen zu bleiben, auch erwachsene Schwarzspitzen-Riffhaie bilden stabile Gruppen für soziale Zwecke und zur Jagd. Ihre Beute sind Fische, Krustentiere, Weichtiere und Tintenfische, aber auch Land- und Seeschlangen und sogar Ratten und Vögel. Sie haben große Augen mit einer reflektierenden tapetum lucidum wie eine Katze, was andeutet, dass sie nachts exzellent jagen können.

Wegen ihres extrem kleinen Reviers und ihrer hohen Standort-Treue sind Schwarzspitzen-Riffhaie anfällig für die Zerstörung ihres Lebensraumes und Fischereidruck (nur als Beifang bei kommerziellen Fischereien, aber gezielt von Kleinfischern für ihr Fleisch, Leber-Öl und Flossen, und auch von Sportfischern und für den Aquarienhandel). Ihre kleinen Würfe (nur 2 bis 5 Junge) und lange Tragzeit (bis zu 16 Monate) sind auch keine Hilfe. Sie werden als “potentiell gefährdet” von der IUCN angesehen. Normalerweise sind sie scheu und trotz ihrer Größe (typischerweise bis zu 1,6 m) keine Gefahr für den Menschen, aber manchmal beißen sie die Beine oder Füße von Watern, die in ihren Bereich eindringen, oder von Speer-Fischern für ihren Fang.

Quellen: hier, hier und hier

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Shark of the week: Blacktip reef shark —

Shark of the week: Blacktip reef shark

The Blacktip reef shark (Carcharhinus melanopterus – derived from melas = black and pteron = wing or fin (see Pterosaurs)) is another requiem shark living in coral reefs. It inhabits nearshore waters of the tropical and subtropical Indo-Pacific from South Africa to Hawaii (even colonized the eastern Mediterranean Sea by way of the man-made Suez Canal) and prefers more shallow waters than its colleagues grey reef shark and whitetip reef shark. Their nursery grounds (females are viviparous and give birth to living young after feeding them from yolk and via placental connection) can be so shallow that the pups have to swim with their dorsal fins above the water looking “like a flotilla of tiny sailboats” (quote from here).

An expanse of clear water and white sand, and several sharks swimming with their black-tipped dorsal fins protruding above the water
Carcharhinus melanopterus by Leon Brocard from London, UK – PIMG_2915, CC BY 2.0, Link

Not only pups prefer to stay in groups for protection, but also adult Blacktip reef sharks form stabile groups for social purposes and hunting. Their prey are fishes, crustaceans, molluscs and squids, but also terrestrial and sea snakes and even rats and birds. They have got large eyes with a reflective tapetum lucidum like a cat, indicating that they can excellent hunt at night.

Due to their extremely small home ranges and strong site fidelity, Blacktip reef sharks are susceptible to habitat degradation and fishing pressure (only as bycatch by commercial fisheries, but targeted by artisanal fishermen for their meat, liver oil and fins, and also by recreational fishermen and for aquarium trade). Their small litter sizes (only 2 to 5 pups) and long gestation periods (up to 16 month) are no help, either. They are considered “near threatened” by the IUCN. They are normally timid and despite their size (typically up to 5.2 ft -1.6 m-) no danger to humans, but sometimes bite the legs or feet of waders encroaching into their space or spear fishers for their catch.

Sources: here, here and here

National Geographic: study about plastic waste| Studie über Plastik-Abfall — 7. October 2017

National Geographic: study about plastic waste| Studie über Plastik-Abfall

Mass production of plastics, which began just six decades ago, has accelerated so rapidly that it has created 8.3 billion metric tons … 6.3 billion metric tons has become plastic waste. (Half of all plastic manufactured becomes trash in less than a year)… Of that, only nine percent has been recycled.

via http://news.nationalgeographic.com/2017/07/plastic-produced-recycling-waste-ocean-trash-debris-environment/

And this recycling can make matters even worse: In China fleece are made of disposable water bottles from Germany (as part of the recycling quota) and sold back to Germany, where they pollute the waste water and lastly the sea with micro fibers (microbeads) due to cleaning and still end up as waste, but already broken down in small particles (instead of after 450 years like the original water bottle).
Waste minimisation instead of recycling, I say!


Die Massenproduktion von Kunststoff, die erst vor 6 Jahrzehnten begann, hat sich so rasant beschleunigt, dass sie 8,3 Milliarden metrische Tonnen erschaffen hat… 6,3 Milliarden metrische Tonnen davon sind zu Müll geworden (Die Hälfte alles hergestellten Kunststoffs wird innerhalb von weniger als einem Jahr zu Abfall)…Davon sind nur 9 Prozent recycled worden.

via http://news.nationalgeographic.com/2017/07/plastic-produced-recycling-waste-ocean-trash-debris-environment/

Und dieses Recycling kann alles noch schlimmer machen: In China werden aus Einweg-Wasserflaschen aus Deutschland (als Teil der Recycling-Quote) Fleece hergestellt und wieder nach Deutschland zurück verkauft, wo sie das Abwasser und letztlich das Meer mit Mikro-Fasern (Mikroplastik) beim Waschen verschmutzen und doch wieder als Abfall enden, aber schon in kleine Teilchen zersetzt (anstatt nach 450 Jahren wie die originale Wasserflasche).
Müllvermeidung anstelle von Recycling, sage ich!

ideas.ted.com: Vertical ocean farms that can feed us and help our seas| Vertikale Meeresfarmen, die uns ernähren können und unseren Meeren helfen — 30. July 2017

ideas.ted.com: Vertical ocean farms that can feed us and help our seas| Vertikale Meeresfarmen, die uns ernähren können und unseren Meeren helfen

Bren Smith wants to create thousands of decent jobs, transform how we harvest food from the oceans, and blunt the effects of climate change and marine degradation — all at the same time. His big idea: small-scale marine farms.

see Vertical ocean farms that can feed us and help our seas — ideas.ted.com


Bren Smith will tausende von ehrlichen Jobs schaffen, verändern wie wir Nahrung aus dem Meer holen, und die Effekte von Klimawandel und Meereszerstörung abmildern- alles zur gleichen Zeit. Seine große Idee: kleine Meeres-Farmen.

Siehe Vertical ocean farms that can feed us and help our seas — ideas.ted.com

Shark of the week: Whitetip Reef shark — 26. June 2017

Shark of the week: Whitetip Reef shark

Another case of mysterious naming is the Whitetip Reef shark (Triaenodon obesus). Not the English name, which is quite apt due to its white tips on dorsal and caudal fins and its exclusive habitat, but the Latin one is untrue: this slender shark is far from obese. On the contrary, as nocturnal hunter it can detect its prey by electroreception (using its ampullae of Lorenzini) and smell (with unique tubular nasal flaps) and follows it into their resting crevices (well adapted to this hunting practice due to its tough skin, sleek build, blunt snout and ridges to protect its eyes), and some sharks “actually squirm into a hole in one side of a coral head and exit through an opening on the other”.

Three gray sharks lying beside each other on the sea bottom.
By Dorothy from USA – sharks, CC BY 2.0, Link

The Whitetip Reef shark is gregarious (sometimes even hunts in groups) and can be seen resting in groups on the bottom or in caves during daytime. It doesn’t need to swim to breathe, unlike other requiem sharks. Not to be confused with the other Whitetip requiem shark (the Oceanic Whitetip), the smaller Whitetip Reef shark (up to 5.6 ft -1.7 m- long) isn’t dangerous to humans. Sadly, as opportunistic feeder it learnt to associate the sounds of boats and spearfishing with food – the curious shark can become bold and agitated and sometimes bites while trying to steal the fish.

Like all requiem sharks, the Whitetip Reef shark is ovoviviparous: every two years 2 to 3 living young are born at a length of 20 to 24 in -52 to 60 cm. There is a case of Parthenogenesis (asexually reproduction) in Whitetip reef sharks. They grow slowly, mature at about 3.4 feet -1.05 m- and live up to 25 years.

Whitetip Reef sharks live in coral reefs all around the world. They are homebodies and famous for their site fidelity. That means that dangers to their coral reef due to climate change, overheating and pollution have a deep impact on the shark population, too, in addition to commercial and recreational fisheries. They are considered as Near Threatened by the IUCN. Conservation measures like marine protected areas (MPA) seems to help, but only if they are completely no-entry. On the Great Barrier Reef, populations of Whitetip Reef sharks in fishing zones have been reduced by 80% relative to no-entry zones. However, populations in no-take zones, where boats are allowed but fishing prohibited, exhibit levels of depletion comparable to fishing zones, most likely due to poaching (IUU). Demographic models indicate that these depleted populations will continue to decline by 6.6–8.3% per year without additional conservation measures.

Sources: here, here and here

Shark of the week: Nurse shark — 27. February 2017

Shark of the week: Nurse shark

Did you know that the Nurse shark (Ginglymostoma cirratum) has the lowest metabolism of all sharks? It needs only 18% of the energy of the agile shortfin mako shark – while swimming. If it swims at all. It is nocturnal and spends the days lazily in its resting sites, together and sometimes on top of many other Nurse sharks.

 

Living in shallow coastal tropical and sub-tropical waters, nurse sharks are bottom-dwelling with two fleshy barbels on the lower jaw (chemosensory organs to help find prey hidden in the sediments). Or they form with their bodies fake caves for prey. These are then sucked in like with a vacuum cleaner. Due to their frugal life they don’t eat much – caught sharks more often that not didn’t have anything in their stomach.

Nurse sharks are brownish in color and reach 7 ft to 10 ft -2.2 to 3 m-, while females are longer than males. They are ovoviviparous, giving birth to 21–29 living young every two years. Like with dogs, scientists found DNA from up to 4 fathers in one litter. Nurse sharks frequent the same nursery and mating areas and resting sites nearby their whole lives (called strong site fidelity), makes them homebodies. They are shy and docile and despite their size no danger to humans, but when provoked, they can bite and are difficult to detach due to the suction.

It seems that the pacific subpopulation of the nurse shark is a species of its own (called Pacific nurse shark), restricting the nurse shark to Atlantic waters only (thus its new name Atlantic nurse shark). Since it doesn’t migrate I wouldn’t be surprised if the Eastern Atlantic subpopulation turns out to be a separate species, too. By the IUCN the Western Atlantic subpopulation is considered as Near Threatened, even as Vulnerable off South America. It is reported locally extinct in some areas off Brazil. Nurse sharks are hunted for their liver oil, fins, flesh and skin and juveniles also for private and commercial aquariums (despite their maximum size). When caught accidentally as bycatch, post-release survivorship is high. Habitat destruction endangers their nurseries and requires additional protective maesures (like in the Florida Keys).

Sources: here, here and here

Shark of the week: Bluegrey carpetshark — 30. January 2017

Shark of the week: Bluegrey carpetshark

Like its sister species, the blind shark, the bluegrey carpetshark or Colclough’s Shark (Brachaelurus colcloughi) shuts its lower eyelids when taken out of the water. Found solely off eastern Australia, it is a rare nocturnal species of the family brachaeluridae (blind sharks).

The bluegrey carpetshark is a stout little shark (up to 30 in -76 cm- long) with long barbels and large spiracles behind its large eyes. While adults are grayish to golden brown above and white below, juvenile sharks have a striking pattern of large black markings on a white background.

As shown in the video, bluegrey carpetsharks are caught for private aquariums, but also sometimes as bycatch in trawl, gillnet and tunnel net fisheries or as game fish by recreational anglers. Due to ist rarity (only 50 specimen have been encountered yet) and small habitat it is particularly vulnerable to urban development pressure, too (like the Port of Brisbane in Moreton Bay).

Moreton Bay Marine Park in Queensland and Cape Byron Marine Park in New South Wales try to preserve this species, but it is considered “Vulnerable”.

Sources: here and here

Shark of the week: Bull Shark — 5. December 2016

Shark of the week: Bull Shark

It is well-known that sharks live in saltwater. Sure, there is such a strange thing as a river shark (like the Ganges shark) that seems to tolerate only fresh water (but, as has been proved, can migrate through saltwater, too). But all other sharks live solely in the ocean or in brackish nursing grounds to protect their young, right? Sadly this is wrong.

Because there is the Bull shark (Carcharhinus leucas). Even if their nursery habitats are in brackish water, older Bull sharks can tolerate high salinity as well as zero salinity, which enables them to live worldwide in coastal areas of tropical to subtropical oceans as well as in rivers and lakes.


(Video S3 of a pregnant bull shark from Brunnschweiler J, Baensch H (2011). “Seasonal and Long-Term Changes in Relative Abundance of Bull Sharks from a Tourist Shark Feeding Site in Fiji“. PLOS ONE. DOI:10.1371/journal.pone.0016597. PMID 21346792. PMC: 3029404., CC by 2.5 )

Bull sharks are able to retain salt through their kidneys, liver, gills and a special gland near their tail (requiring a greatly increased production of highly dilute urine and is energetically very demanding). That’s the reason they survive and even thrive in fresh water as much upstream as 2,360 miles -3,800 kilometres- up the Mississippi River or 2,610 miles -4,200 kilometres- up the Amazon River. There is even a population of Bull sharks in the Lake Nicaragua in Central America, seemingly separate, but tagging showed that they wander between the lake and the Caribbean Sea back and forth, conquering 8 rapids on the way. Since a flood in the 1990s even a golf course lake in Queensland, Australia is the home to several bull sharks.

The Bull shark is a stout species with small eyes and a blunt snout (thus the name) and an average length of 7.9 ft – 2.4 m- (female) and 7.4 ft -2.25 m- (male), but there is a single record of a pregnant female specimen of 13 ft -4 m- in an African river. Their age of maturity seems to be varying according to geographic location, up to 14-15 years for males and 18 years for females. Bull sharks are ovoviviparous, like other requiem sharks.

Being opportunistic feeders, Bull sharks eat everything from bony fish and other sharks (even young Bull sharks), to turtles, birds, dolphins and terrestrial mammals like dogs and hippos, but also carcasses and (in case of Indian rivers) bodies. They have to (as mentioned above) in order to survive in fresh water with its zero salinity and significantly greater negative buoyancy. In the ocean their metabolism can slow down.

Based on their habitat, Bull sharks come in frequent contact with humans. In the clear waters of the Bahamas, for example, divers regularly interact with crowds of bull sharks without problems. Some researchers speculate that this non-threatening behavior may be because the sharks can clearly see people and recognize that they are not a typical food source. In murkier waters, however, incidents happen, and humans get bitten and sometimes die. Some Bull sharks being territorial and having virtually no tolerance for provocation doesn’t help matters, either.

Due to its habitat, but also its size, strength and teeth, the Bull shark has been considered by many experts to be the most dangerous shark in the world. If there is such a thing as a Man eater shark it would be the Bull shark and not the White shark. The latter may not in fact be responsible for many of the attacks pinned on the species (including the famous 1916 shark attacks in New Jersey that may have served as inspiration for Jaws), but the Bull shark with its nearly identical dentition. It’s amazing that we don’t have more incidents, and it just reconfirms that they really aren’t interested in us and usually an attack is a mistake.

The Bull shark is caught as bycatch in longline-fisheries, but more often targeted in small artisanal fisheries because of its abundance in nearshore environments and rivers for its meat, fins and skin. Additionally, it is a popular game fish. Due to pollution of their habitat in shallow costal waters, rivers and lakes, and overfishing of their nursery grounds, Bull sharks numbers have significantly declined.

Sources: herehere, here and here

Shark of the week: Ganges shark — 31. October 2016

Shark of the week: Ganges shark

Sharks live in every ocean. Some like it hot (like the pacific sleeper shark), others adapted to freezing temperatures (like the greenland shark). Some doesn’t mind fluctuating saline levels (like the pyjama shark). But did you know that there are river sharks? That are sharks living solely in freshwater. One of them is the Ganges shark (Glyphis gangeticus).

FMIB 45519 Carcharinus gangeticus.jpeg
Ganges shark von Edgar Ravenswood Waite – Waite, Edgar R. (1921) Illustrated Catalogue of the Fishes of South Australia, Adelaide, Australia: G. Hassell & Son, Gemeinfrei, Link

This species of requiem shark lives in Indian rivers and has been accused to be a “man-eater”. But it has been most likely confused with bull sharks, since its slender teeth imply that its prey are rather small fish. It is a up to 6.6 ft – 2 m – long grey to brownish shark with minute, upward tilted eyes.

Pollution and utilization of its habitat and fishing pressure are dangers to the extremely rare Ganges shark. It is considered Critically endangered.

Recent genetic tests show that river sharks from Borneo (Borneo river shark) and Myanmar (Irrawaddy river shark) are the same species as the Ganges shark. Two recent gene flow events in the central Indo-Pacific (between Myanmar and India and Pakistan and Java) and a third, older event that resulted in the colonization of Australian rivers, prove that river sharks can migrate through saltwater. Perhaps all river sharks can live in the ocean, but choose to seek shelter for themselves and their young in rivers.

Sources: here and here

What seafood to eat | Welchen Fisch essen -Outside Online — 14. September 2016