Shark’s Electroreception

Like many fish sharks also have another sense, a sixth sense, which we don’t know much about. They are able to detect tiny electrical impulses in the water. As all animals produce some electrical signals this can be very useful! They can detect movement in the water from hundreds of meters away. They can pick up electrical signals generated by their prey, making it possible to feel other animal movements.

This sixth sense is made possible thanks to electro-receptive organs called Ampullae of Lorenzini. These were discovered only recently. The Ampullae are jelly-filled pores. These pores are located all around their heads with a greater concentration around their snouts and are connected to the brain through nerve endings. Basically, these ampullae are electrical field-sensing devices. Every living creature produces an electrical field which sharks can detect.

Strangely enough, a shark will sometimes attack a metal object. This is because, in salty seawater, metal gives off electric signals, which confuse the shark into thinking it is prey. This means a shark cannot only detect its prey but a diver or potential hunters without seeing them.

Shark is a kind of fish that is protected. You can find them on  places like sea world. They take care sharks, of course unlike birds, dogs, cats or goldfish, sharks have special needs. Got interested with shark and other fish? Well you should, because fish are fantastic animals and you can have them as your pets.

Sharks are different with other fishes

  • Sharks and rays do not have true bones like other fishes. They have cartilage instead which is lighter and much more elastic and allows them to bend in very tight circles.

  • Sharks do not have swim bladders. A swim bladder is a gas filled sack inside the body of bony fishes that allows them to stay still without sinking. Sharks compensate by having a very big liver that is filled with oil. Even so, sharks sink unless they keep swimming forward. The exception is the Sandtiger Shark which swallows air to make itself more buoyant.

  • A shark’s upper jaw is not fused to its skull like most animals. When a shark bites a large object, it is able to move its upper and lower jaw forward in order to take a bigger bite.

  • Unlike other fishes, sharks are able to replace their teeth constantly. New teeth grow from the inner surface of the jaw and rotate forward when the old teeth get worn out or lost during feeding.

  • Sharks and rays do not reproduce like other fishes. Most fish release clouds of sperm and eggs into the water column where they mix together. The fertilized eggs then float around until the fish larvae hatch and form schools of tiny fish. Male sharks have two organs called claspers attached to their anal fins. They insert one of these into the female shark’s cloaca (the entrance to the uterus) to transfer sperm (just like in mammals). Some sharks and rays incubate the eggs in their uteruses until the baby sharks are ready to be born. Other sharks and rays (i.e. skates) lay eggs and attach them to the reef.

  • Sharks have between 5 and 7 gill slits on each side of their body in front of their pectoral fins. Bony fishes only have one pair. Having many exposed gill slits probably helps transfer more oxygen into their blood faster which allows them to swim very fast when they need to.

  • Most shark’s skin is covered in small denticles instead of scales. Denticles are a lot like teeth. They have dentine in the centre and enamel on the surface. This makes shark’s skin very tough and abrasive like sandpaper. The shape and position of some shark’s denticles also helps reduce friction so that they can slip through the water easier.

  • Sharks have an extra sense that is able to detect tiny electric fields. They can use this to find food that is buried or to search for animals to eat in the dark or in turbid water.

  • Sharks and rays make up the sub-class of fishes called elasmobranches. This sub-class is part of a class of cartilaginous fishes called Chondrichthyes which also includes chimaeras (ratfishes).

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Shark Finning

Finning is called as the cruel cutting off the fins of the sharks. Often the sharks are still alive at this time. The trunk of the shark (dead or alive) is then thrown as redundant ballast over board. The shark fins constitute only approx. 14% of the total weight of a shark but bring in on the international market substantially more than shark meat. The fins are used exclusively for shark fish fin soup. Finning is cruelly however lucrative; for a kilo of shark fins in Asia an average over 100 US Dollar is paid.

Hong Kong and the mainland China dominate the world-wide shark fin market to 50%. Statistics from Taiwan, Singapore

and Hong Kong point a growth like an explosion of the trade with shark fins. Already 1999 according to official data of the customs authorities of Hong Kong 6954 tons of shark fins were released for the re-export. The number of exported fins might have increased by a multiple since then. They predominantly go to Taiwan, Singapore, Malaysia, Korea and China. Taiwan ranks at place five in the world-wide shark fin trade. It maintains the world-wide largest fishing fleet, which fishes primarily in international waters, far away from the own territorial waters.

Shark Products

Over 100 million sharks are killed annually. Partly because of their fins for shark fish fin soup, as bycatch in up to 40 miles long drift nets of enormous fishing fleets, for medically completely ineffective cartilage powder or by the destruction of their habitats.

You will find shark products often at unexpected places as in restaurants, snack bars or supermarkets. Shark meat is offered also under various other names as Smoked Rock Salmon, Smoked Dogfish, a component of Fish & Chips or Imitation Crab Meat (Surimi). Also the worldwide protected and extremely threatened whale shark is on the Asian market (mainly Taiwan and Japan) still offered as Tofu Shark.

Besides the British the Germans consume most spiny dogfish. They produce the so-called “Schillerlocken” out of the sharks belly. The British use the spiny dogfish for “Fish & Chips “. This kind of shark is strongly overfished and its existence in the Northeast Atlantic decreased in the last 40 years by 90 percent.

Principal customers for shark fins are mainly eastern cultures in which shark fin soup represents a cultural meal. It is a remarkable fact that a shark fin, which consists to 90% out of cartilage, is extensively tasteless and only after days of boiling up in a broth becomes soft and gets the taste of the broth. Today shark fin soup is a status symbol because of the strongly risen prices within the last few years.

We can find shark products also in dog fodder, fish flour and even in fertilizers. From shark skin leather products such as purses, shoes or clock bracelets are produced.

Shark liver oil is frequently a component of the well-known cod-liver oil. In the health sector shark cartilage powders is marketed as fit making food additive although shark cartilages contains absolutely no fit making or other wholesome ingredients.

Most problematic is the marketing of shark cartilage as an anti-cancer means. The publication “Cancer Research” published in December 2004 confirms that shark cartilage preparations showed absolutely no effect against cancer.

However in the gel sector (food/pharmacy) shark collagen has few market chances although particularly Spain tries to penetrate into the market with shark collagen. Spain, one of the world largest shark fin producer, has 2002 forbidden to bring only the fins of sharks ashore. According to law the whole shark bodies must be brought now ashore. This leads now ridiculous-proves to the fact that out of the bodies the completely ineffective cartilage powder is made perforce.

In the cosmetics sector from shark cartilage won collagen is used for anti-fold creams and other preparations. Collagen from sharks is free of BSE and more kosher which makes it interesting for the Arab and Israeli markets.

A STING IN THE TALE FOR SHARKS AND RAYS

Expert findings show sharks and rays are now amongst Europe’s most threatened animals as more are added to the IUCN Red List of Threatened Species

Gland, Switzerland, 20 February 2006 (IUCN)  The number of species of sharks and rays on the IUCN Red List of Threatened Species will increase based on the findings of a three-day expert workshop, hosted by the Joint Nature Conservation Committee (JNCC), that examined the conservation status of the species in the Northeast Atlantic and Mediterranean waters.

The workshop confirms the widely-accepted notion that slow-growing sharks and rays are exceptionally vulnerable to over-fishing, and that deep-water species are being depleted at an alarming rate. Some formerly important commercial species are now so rare that they are no longer being sought by fishermen, but their risk of extinction is still rising because of continued incidental capture in fisheries for more abundant species. This situation is exacerbated by the lack of shark fisheries management in European waters.

“Sharks and rays are amongst the most threatened animal groups in the UK today. I welcome the development of a Red List baseline, against which to monitor the hoped-for changes in their status that should arise from increased awareness of their plight,” said Dr Malcolm Vincent, JNCC’s Director of Science.

Nearly 100 species of sharks and rays were evaluated against the IUCN Red List Categories and Criteria. Categories range from Extinct to Least Concern and Data Deficient. Species deemed Vulnerable, Endangered or Critically Endangered are considered threatened with extinction and are added to the global IUCN Red List of Threatened Species. The IUCN Shark Specialist Group, which convened the meeting, will compile these assessments for a regional report that will include recommendations for conservation action.

Proposed additions to the Red List include three species of angel sharks, two species of skates, and several species of deep-water sharks, all of which are considered Critically Endangered in the region, as well as two species of coastal ray, now considered Endangered. The species found to be at lowest risk were generally small and fast-growing coastal species, like cuckoo ray and lesser-spotted catshark, and very deep ocean species that are still beyond the reach of today’s fishing fleets.

Angel sharks, formerly abundant large coastal sharks, were once a common sight in fish markets, but have largely vanished, almost unnoticed, from the European seas that are their world stronghold.

Now officially declared extinct in the North Sea by the International Council for the Exploration of the Sea (fisheries advisers to European countries), the angel shark was nominated in 2001 for strict legal protection in British waters, but we are still waiting for government action on this proposal, said Sarah Fowler, Co-Chair of the Shark Specialist Group. Workshop participants emphasised the urgency of protecting this, and many other imperilled species.

Three species of deep-water sharks, taken as incidental catch in fisheries and increasingly targeted for their meat and rich liver oil, were assessed as threatened. A population decline of 80-95% prompted a Critically Endangered classification for the region’s deep-water gulper shark.

These exceptionally slow-growing sharks are simply not biologically equipped to withstand such intense fishing pressure, said Tom Blasdale, Marine Species Adviser at the JNCC. We welcome recent European Union action to manage deep-water gillnet fisheries, but similar measures are still urgently needed to protect deep-water sharks taken by trawls and longlines.

The shortfin mako shark, a favourite target of commercial and recreational fishermen around the world, was proposed as Vulnerable in the Northeast Atlantic and Critically Endangered in the Mediterranean Sea.

This wide-ranging species is increasingly the target of fisheries and yet lacks any type of protective measures in this region, warned Alen Soldo of the Institute of Oceanography and Fisheries in Croatia. Of particular concern are mako sharks in the Mediterranean, where our findings revealed ongoing fishing pressure well beyond the reproductive capacity of the species.

In contrast to similar workshops held in North America, South Africa, and Australia, the workshop yielded little if any good news, due largely to the lack of shark and ray conservation measures in this region. Protection is granted by just a handful of European countries for the three largest species (basking shark, devil ray, and great white shark). The few European shark and ray quotas in place are routinely set far in excess of actual catches and therefore do not limit fishing pressure. They also cover only part of these stocks. Scientists advice for zero catch of many depleted shark and ray species has been ignored. There are no international limits on shark catch, even as fisheries for wide-ranging shark species (such as mako and blue sharks) expand and evidence of their declines mounts.

Scientists from government agencies, universities, and private institutions participated in the workshop including authors of published papers on shark and skate population status and experts who develop advice on shark quotas for European and international fisheries of the Northeast Atlantic. Experts from England, Scotland, Ireland, Italy, Spain, Portugal, Croatia, Russia, Sweden, Canada, and the USA took part.

The IUCN Red List of Threatened Species is the world’s most authoritative guide to the status of biological diversity. The workshop was the eighth in a global series to assess all of the world’s shark and ray species and develop regional conservation priorities. Resulting Red List proposals are preliminary until accepted by the global Shark Specialist Group network.

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