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.

Basics of Sharks

  • Sharks have roamed our seas for more than 400 million years, which means they inhabited the earth for nearly 200 million years before dinosaurs.
  • Sharks are fish with skeletons made of cartilage instead of bone, but sharks’ slow growth and late maturity mean they have more in common with sea turtles and marine mammals than bony fish such as flounder or tuna.
  • Sharks are a remarkably diverse group of fish. They range from less than a metre to 20 metres in length; they are found in most coastal regions but also in the deep ocean and even in fresh water. Some sharks lay eggs, but most give birth to live young. Most are top predators while a few feed on plankton. Sharks in turn are preyed upon by other sharks and sometimes killer whales.
  • The term ‘shark’ often refers not only to shark species but also to the closely related rays and skates, as well as the oft-overlooked chimaeras (rat, rabbit and elephant fish).Collectively these cartilaginous species are known as chondrichthyan fish (forming Class Chondrichthyes).

The Shark Trust

The Shark Trust was established in 1997 to study, protect, and manage the elasmobranch species found in UK waters and internationally. It is a member of the European Elasmobranch Association and works with other EEA organizations to counter the enormous fishing pressure that European shark and ray stocks are under.

The Shark Trust’s mandate includes:

  • Introducing effective management on a regional basis to regulate shark and ray fisheries and ensure that they are sustainable.

  • Reducing shark and ray bycatch and mortality in other fisheries.

  • Increasing research efforts on the biology of sharks and rays and their fisheries, including the promotion of a collaborative tag and release program.

  • Improving records of catches, landings, and international trade in species of sharks and rays.

  • Improving management of critical habitats, including nursery grounds, under threat.

  • Increasing the amount of information available to the public and decision makers.

The Shark Trust encourages scientists, divers, fishermen, anglers, and the general public to join the growing number of ST members that currently lend their support.

Your membership in The Shark Trust adds to the pressure that it is able to be put on governing and regulatory agencies, and helps spread awareness on the plight of sharks and rays in general.

Subscription to The Shark Trust carries no obligation on your part unless you wish it to. However, if you would like to help educate or raise funds your added contribution will be most welcome.

Shark Trust members receive the trust’s magazine/newsletter ‘Shark Focus’ 3 times per year. This is a glossy publication that chronicles the latest work of the trust and has articles on a variety of shark and ray subjects. Upon joining the trust you will also receive i.d. posters of British shark and ray species and other Shark Trust goodies.

The Shark Trust also hosts a highly informative website with sections on all aspects of sharks and rays. The site also contains a good image database of elasmobranch species and an active and well moderated forum for anyone wishing to talk sharks.

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.

Killing Sharks

Sharks have a great deal to fear from humans. Compared to the 10-15 people killed by sharks each year; over 100 million sharks perish at the hands of humans annually and many populations may face extinction. Sharks are killed for many reasons, including fear; food, sport, and ‘machismo’, but the great majority perish due to simple greed. Many shark products have commercial value, including: the flesh; the skin for high-quality leather; teeth and jaws for ornaments; liver oil for cosmetics, medicines, vitamin A, and skin-care products; and cartilage for false cancer ‘cures’. However; the product that drives the market are the fins. After drying, collagen fibers are extracted from them, cleaned, and processed to make ‘shark fin soup’. In spite of the fact that these fibers have little flavor or nutritional value, the soup is considered a delicacy, and may sell in the Orient for more than $100 ( £65) a bowl.

Over the years, shark fisheries have come and gone. In the early part of the century, sponge fishermen in Florida killed sharks to boil them down for their oil. The oil was then thrown on the ocean to smooth the surface of the water and make it easier to see the sponges from the boat. That ended when a plague killed off the sponges. In the 19405 to .19505 a number of shark fisheries sprang up to supply the market for vitamin A. That ended with the discovery of a method for its synthetic production. However; most shark fisheries, such as the one for dogfish sharks to supply the ‘fish and chips’ market in the UK, have ended only when the number of sharks dropped too low for the fishery to be sustained.

The explosive growth of the Chinese economy and rapid expansion of trade with the outside world during the 1985 and 1995 created an unprecedented situation. Suddenly there was an insatiable demand for shark fins of almost any size or type. Improvements in shipbuilding and navigational electronics meant that shark fishing boats could now go anywhere in the world, moving from one place to another as local shark populations were destroyed. The fins are now so much more valuable than the rest of the shark that the carcass is often discarded after the fins are removed, to save storage space on the boat. Often the fins are sliced off when the shark is still alive and the mutilated shark is dumped back into the water to die a slow and agonizing death.

Why should we be concerned about this situation? After all, wouldn’t the ocean be much safer without sharks? The answer is no. The chance of being attacked by a shark is already less than the chance of being struck by lightning. The real dangers for people in the water are drowning, exposure, and being struck by a boat. In the USA, for example, drowning incidents outnumber shark attacks by 1,000 to I. Without sharks, the whole experience of being in a natural ocean wilderness would be immeasurably reduced. It would be like being on the Serengeti with no lions or cheetahs. In losing the opportunity to view these magnificent and superbly-adapted predators in the wild, we are also losing part of our spiritual connection with nature.

But something else would be changed as well -the whole ecology of the ocean. Predators control the populations of their prey species in a beneficial way. They eliminate diseased and genetically defective individuals, and they stabilize population fluctuations. On land, when we have removed the natural predators of deer; for example, their populations have exploded until they overgrazed their food supply and died of starvation and disease. In the ocean we are not sure what all the consequences of removing the apex predators from the food pyramid might be. We do have one example, though. A shark fishery in Tasmania collapsed after two years of over fishing. Shortly afterwards, the fishery for spiny lobsters also collapsed and fishermen observed a lot of octopus in the area. Octopuses are both major predators of spiny lobster and an important food item for sharks. It seems that once the numbers of octopus were no longer controlled by the sharks, they became too numerous and decimated the lobsters. Economically, for those other than shark fishermen, it doesn’t make sense to allow sharks to be fished out, not only because of the possible damage to sustainable fisheries, but also because of the loss of earnings from divers coming to see sharks. Worldwide, shark-watching has become a multi-million dollar business.

Why do shark populations collapse so quickly when people begin fishing them? The answer lies in the life history of these animals. In many aspects, sharks are more similar to mammals such as whales, dolphins, or ourselves, than to other fish. Whereas most fish reach maturity in only a few years and produce thousands or millions of eggs per year; sharks take many years to reach maturity. Some species may not begin to reproduce until they are over 15 years old. Some species produce as few as two pups biannually, averaging only one offspring per year: So when a population is over fished, it may take many years to recover; or it may never recover: Some scientists believe that sharks should never be fished at all, that their biology is too fragile to withstand any exploitation. Perhaps sharks should have the total protection given to marine mammals in many countries. Unfortunately, sharks do not have big ‘fan clubs’ as dolphins do.

Although both are large predators with slow reproductive rates, sharks are handicapped, from a.: public relations perspective, by the fact that their mouths appear to be frowning, and that they must open their mouths to pass water over their gills, exposing their teeth. Dolphins, on the other hand, always appear to be smiling, because of the shape of their mouths. Since they breathe through the blowholes on top of their heads, they do not have to open their mouths and expose their formidable teeth in order to get oxygen. But even the dolphin’s smile may not protect it from the greed inspired by the high prices being offered by international buyers of shark fins. In a number of countries, fishermen are slaughtering dolphins to chop up for shark bait.

We should create save our sharks and dolphins lanyards to create awareness