save our blue planet

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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
Pew: Cartoon crash course about ocean terminologies — 23. August 2016
6 amazing plastic bans from around the world – and Germany? — 11. August 2016

6 amazing plastic bans from around the world – and Germany?

Good news! Plastics bans across the world have been hitting the headlines lately.From the US to India and Morocco, governing bodies are taking control of the plastic pollution problem, bringing in either complete bans on plastic, or bans on specific forms like polystyrene.

Source: 6 amazing plastic bans from around the world

In Europe, we try to reduce the plastic waste, too, to protect the ocean from waste pollution. Especially the colorful plastic shopping bags the cashier throws at you for free. Every European uses 200 of them each year, most of them only once. But since the EU leaves it to their members how to do it, Germany uses its standard methods: personal commitment of the firms (freiwillige Selbstverpflichtung, that means they make a non-binding promise of their own to prevent a law) and money. Instead of banning these bags, the customer can use them further but in some markets he has to buy them first. Many markets offer canvas shopping bags, too, but they are more expensive. Guess what will happen?

I’m afraid it will end like with plastic bottles: instead of banning single-serving water bottles Germany put a deposit on them, just like on reusable PET bottles. And what happened? The quota of reusable water bottles decreased, of course. Many customers don’t differentiate between the two and use the lightweight single-serving bottle rather that the heavier reusable bottle, since it is all the same anyway.

Take the pledge and use no plastic shopping bags anymore – with time it becomes second nature to take your own bag with you (even if you have to interrupt the cashier in its routine to prevent getting another bag). And be proud about yourself for every disposible bag you don’t have used.

Every step counts.

No oil from the US Arctic? – Greenpeace International — 29. July 2016

No oil from the US Arctic? – Greenpeace International

via Don’t look now, but there was just a mass exodus of oil companies from the US Arctic | Greenpeace International

Only Shell didn’t gave up yet, but since cleaning Arctic oil-spills is impossible due to the climatic conditions and the U.S. government estimated the runtime risk of a large oil spill as 75%, I hope they change their mind, too. But is it in the face of such opinions a realistic hope?

Greenpeace about microbeads | Greenpeace über Mikroperlen — 23. July 2016

Greenpeace about microbeads | Greenpeace über Mikroperlen

Did you know that microbeads are used in cosmetics not only to exfoliate (which I can comprehend, even if they should use other, natural particles), but also simply for color and texture? Manufacturers seem to think that customers like their liquid soap, shower gel or shampoo smooth and thick (viscid), even if it has got no cleaning benefit and only environmental drawbacks. We use a special, ph-neutral liquid soap together with a reusable foam soap dispenser and it works fabulously. Sadly, my daughter likes glitter in her pink shower gel (girls 😉 ), I don’t know how to make that myself.

Greenpeace addresses the problem of microplastic in cosmetics here more detailed than I did and also describes the loopholes manufacturers use to deceive us. Unfortunately, the mentioned guide to avoid cosmetics in question seems to work only in UK and Australia.


Wusstest Du, dass Mikroperlen in Kosmetik nicht nur zum Peelen benutzt werden (was ich nachvollziehen kann, auch wenn sie andere, natürliche Partikel benutzen sollten), sondern auch einfach für die Farbgebung und Textur? Die Hersteller scheinen zu denken, dass der Kunde seine Flüssigseife, Duschgel oder Shampoo glatt und zähflüssig mag, auch wenn das keinerlei Reinigungs-Nutzen sondern nur Umwelt-Nachteile hat. Wir nutzen eine spezielle, ph-neutrale Flüssigseife zusammen mit einem nachfüllbaren Schaum-Seifenspender und es geht wunderbar. Leider mag meine Tochter Glitter in ihrem pinken Duschgel (Mädchen 😉 ), Ich weiß nicht, wie ich das selbst machen kann.

Greenpeace spricht das Problem von Mikroplastik in Kosmetikprodukten hier detaillierter an als ich es getan habe, und beschreibt auch die Hintertürchen, die die Hersteller nutzen um uns zu täuschen. Hier auch etwas dazu auf Deutsch. Bedauerlicherweise scheint der erwähnte Leitfaden zum Vermeiden von fragwürdiger Kosmetik nur in Großbritannien und Australien zu gelten.

Shark of the week: pigeye shark — 6. June 2016

Shark of the week: pigeye shark

Did you know that nearly every reef fish can contain toxins produced by dinoflagellates that cause food poisoning called Ciguatera? The toxins cannot be identified by odor, taste or appearance, are transferable sexually, by breast milk and across the placenta and cannot be eliminated by cooking, freezing, salting, drying, smoking, marinating or waiting. The higher up in the food chain, the more toxin the fish contains (by accumulation and biotransformation), which explains that a pigeye shark caused an outbreak of Ciguatera in Madagascar with 500 victims and a death toll of 20 percent in November 1993. Normally this disease causes only neurological or gastrointestinal problems, sometimes recurring or persisting for months or even years (with a death toll up to 2 percent), but shark as a large predator is obviously deadlier. Exported reef fish (supposedly also farm-raised salmon from Chile), unusual fish migration as well as tourism accounts for cases outside the tropics or subtropics, often resulting in insufficient treatment due to unknown and therefore misjudged symptoms (sometimes misdiagnosed as multiple sclerosis). Annually 20 000 to 50 000 people worldwide are suffering from this disease (which is surely an underestimate because of missed diagnoses and underreporting).

The pigeye shark is a species of requiem shark that lives in the tropical and subtropical marine waters of Eurasia, Africa and Oceania and is up to 8.2 ft -2.5 m- long.

Carcharhinus amboinensis ranong.jpg
By Tassapon KRAJANGDARA on www.fishbase.us, CC BY 3.0

The pigeye shark is viviparous, and after the developing embryo depletes its supply of yolk it is sustained to term by its mother through a placental connection formed from the empty yolk sac. After a gestation period of 9 to 12 months the female gives birth to 3 to 13 pups, using sheltered habitats as nurseries. The pigeye shark is a top predator, and it’s size and teeth make it potentially dangerous, though it has not been known to attack humans – if you don’t eat it.

Sources: herehere and here