Scientists Trace Origin Of Shark’s Electric Sense
The dark markings indicate gene expression in the electrosensory organs in the head of an shark.
Gainsville, Florida (Feb 6 2006 18:53 EST) Sharks are known for their almost uncanny ability to detect electrical signals while hunting and navigating.
Now researchers have traced the origin of those electrosensory powers to the same type of embryonic cells that gives rise to many head and facial features in humans.
The discovery, reported by University of Florida scientists in the current edition of Evolution & Development, identifies neural crest cells, which are common in vertebrate development, as a source of sharks’ electrical ESP.
It also fortifies the idea that before our early ancestors emerged from the sea, they too had the ability to detect electric fields.
“Sharks have a network of electrosensory cells that allows them to hunt by detecting electrical signals generated by prey,” said Martin Cohn, a developmental biologist with the departments of zoology and anatomy and cell biology, and the UF Genetics Institute. “That doesn’t mean they can only detect electric fish. They can sense electricity generated by a muscle twitch, even if it’s the weak signal of a flounder buried under sand.”
Likewise, sharks are widely thought to use the Earth’s magnetic field for navigation, enabling them to swim in precise paths across large expanses of featureless ocean, Cohn said.
“If you think of this in the big picture of evolution of sensory systems, such as olfaction, hearing, vision and touch, this shows sharks took a pre-existing genetic program and used it to build yet another type of sensory system,” Cohn said.
UF and University of Louisiana researchers analyzed electroreceptor development in the embryos of the lesser spotted catshark, an animal that is largely motionless during the day and hunts at night, mainly in the seagrass beds of the eastern Atlantic Ocean.
Using molecular tests, scientists found two independent genetic markers of neural crest cells in the animal’s electricity-sensing organs. Analysis shows these cells migrate from the brain and travel into the developing shark’s head, creating the framework for the electrosensory system – a previously unknown function of a much-studied group of cells, according to Renata Freitas, a doctoral candidate in UF’s zoology department and first author of the paper.
The process mirrors the development of the lateral line that allows fish to mechanically sense their environment, and organs of the inner ear that enable people to keep their balance. But scientists suspect as human ancestors emerged from the sea, they discarded their lateral lines as well as their ability to sense electrical fields.
“Our fishy ancestors had the anatomy for it,” said James Albert, a former UF biologist who is now at the University of Louisiana. “You can imagine how valuable this system would be if you were aquatic, because water is so conductive. But it doesn’t work on land – air doesn’t conduct electricity as well. When it happens, it’s called a lightning bolt and you don’t need special receptors to sense it.”
All primitive animals with backbones could sense electricity, according to Michael Coates, an associate professor of organismal biology and anatomy at the University of Chicago. Mammals, reptiles and birds lost the sense over time, as did most fish alive today.
But in sharks and a few other species, such as sturgeons and lampreys, electrosensory capability endured.
“Most fish you see today have large eyes,” Coates said. “But sharks are predators that do not particularly rely on vision. If you see a hammerhead shark searching for flatfish, it moves its head back and forth, almost as if it were using a metal detector. Knowing that the electrosensory system may have developed with involvement of neural crest cells is valuable for people trying to reconstruct vertebrate evolution. It gives us further indication of how all of the various sensory systems come on line.”
But the idea that the neural crest truly is the source of the electrosensory system will raise eyebrows, scientists say.
“It’s a very interesting paper for two reasons,” said Glenn Northcutt, a distinguished professor of neuroscience at the University of California, San Diego, and a leading expert in vertebrate neurobiology. “For the first time, someone has shown which molecules may be responsible for guiding the development of the receptors of the lateral line system. I think this will hold true and is a very important finding. But I’m skeptical about the claim the neural crest gives rise to electroreceptors. It still requires a definitive experiment, where the developing neural crest cells are marked with dye, the embryo develops and the dye clearly shows up in the electroreceptors.”
Dye tests are a classical way of mapping cell movements during development, and have been used to explore the origins of limbs and brain cells. In the current research, scientists used genetic markers to trace neural crest cells.
Filed under Save Sharks · Tagged with ability, action, aim, air, amp, anal, Analysis, anatomy, animal, Atlantic, author, balance, biologist, biology, bolt, bone, brain, Build, California, candidate, capability, car, catshark, cell, Chicago, claim, Class, Co, crest, day, department, detector, Development, developmental, developmental biologist, discovery, Don, Dye, ear, earth, eastern Atlantic Ocean, edition, electric fish, electrical field, electrical signals, electricity, electroreceptor, electrosensory, embryo, embryonic cells, environment, ESP, EST, Evolution, experiment, expert, expression, eye, fact, Feb, field, fin, finding, fish, fishy, flatfish, Florida, florida feb, florida scientists, form, framework, function, Gainsville, gel, gene, gene expression, genetic program, Genetics, genetics institute, Glenn, group, hammerhead, head, hearing, hold, hunting, idea, Important, indication, Institute, involvement, James Albert, land, lateral, lightning, line, Louisiana, louisiana researchers, Mammals, Martin Cohn, mean, metal, Michael Coates, molecular tests, movement, muscle, muscle twitch, navigation, need, Network, neural, neural crest cells, neurobiology, neuroscience, night, North, Northcutt, ocean, olfaction, organismal, organs, origin, paper, part, picture, power, predators, prey, process, professor, program, rat, rate, reason, Red, Renata Freitas, report, research, researcher, rest, rise, row, San Diego, sand, Science, sea, seagrass beds, sense, sensory system, sensory systems, shark, Sharks, Sharks Electric Sense, signal, someone, source, Species, system, time, today, touch, travel, type, University, university of louisiana, US, use, vertebrate, vertebrate development, vision, water, way, Wide, With, work, zoology
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.
Filed under Save Sharks · Tagged with abundant species, action, addition, advice, Adviser, age, air, Alen, angel, angel sharks, animal, animal groups, assessment, Atlantic, Australia, author, awareness, baseline, Basking, basking shark, Biological, blue, blue sharks, British, capacity, capture, catch, Categories, catshark, cent, Chair, Class, classification, Co, coast, commercial species, committee, Concern, conservation, conservation action, Continue, contrast, Council, Criteria, Critically, Croatia, cuckoo, Data, day, decline, deep ocean, Deficient, Development, devil, Director, diver, dr malcolm, Dr Malcolm Vincent, ear, Endangered, England, EST, Europe, European, european waters, exception, excess, expert, expert workshop, Exploration, Extinct, extinction, favourite, Feb, February, fin, finding, fish, fisheries, fisheries management, fishermen, fishing, fishing fleet, fishing fleets, fleet, form, gel, gene, general, gill, gillnet, Gland, gland switzerland, Government, Great, great white shark, group, gulper, hand, handful, hold, host, Important, Institute, International, Italy, IUCN, iucn red list, iucn shark specialist group, JNCC, Join, Joint, joint nature conservation committee, lack, land, Least, leg, line, List, liver, liver oil, longline, longlines, mako, mako sharks, management, Marine, market, meat, Mediterranean, Mediterranean Sea, mediterranean waters, meeting, Nature, need, Network, news, North, North America, North Sea, Northeast Atlantic, notion, number, ocean, Oceanography, official, oil, Ongoing, paper, part, place, plight, population, Portugal, pressure, product, proposal, Proposed, protect, protection, range, rat, rate, ratio, ray, reach, recreation, Red, region, report, rise, risk, round, row, Sarah Fowler, Science, Scotland, sea, serv, shark, shark fish, shark fisheries, shark specialist group, shark species, Sharks, shop, shortfin, side, sight, situation, skate, skates, skin, Soldo, South Africa, Spain, Specialist, Species, species of sharks, stand, status, stronghold, Switzerland, TALE FOR SHARKS, target, Tens, threat, Threatened, today, Tom Blasdale, type, UK, Union, urgency, US, USA, use, Vulnerable, water, water sharks, water species, White, white shark, Wide, With, work, workshop, world
SHARKWATER FILM
The Canadian born photographer and filmmaker never held a video camera before he began the Sharkwater project — but that is not apparent when you see the film. On the contrary, the imagery is beautifully framed, inspiring, and stunningly breathtaking. The images that Stewart sets forth will awe you, and will capture your heart.
Stewart set out to create a film that would simply depict how beautiful sharks are in their natural habitat. The finished product, however, ended up evolving into so much more. Instead, we’re drawn into an amazing story of human drama, organized crime, corruption, and greed.
The film kicks off with clips from military training videos archived from the 1960s. As might be expected, they depict sharks as ruthless and bloodthirsty man-eaters. The clips belie the ignorance of their times with suggestions such as putting one’s face in the water and yelling to deter a marauding shark.
While it provides an almost humorous relief to the serious subject matter, it is important to realize that 40 years ago, these films were definitive and authoritative. Forty years ago, we held these precepts to be truth. We look back and laugh, because now we know better. …Or do we?
The chasm between reality and the popular beliefs sustained and fueled by exaggerated media is still enormous.
In reality, sharks do not eat people, and they are not mindless killers. As long as people view sharks as dangerous predators, they won’t care about saving them, and this is exactly what Rob Stewart hopes to change.
Early in the film, Stewart begins to debunk some of the mystery and fear around sharks as he holds and pets an eight foot long Caribbean reef shark as if it were a lapdog. From this point on, his understanding of sharks and his community with the underwater world is evident.
In an effort to capture even more compelling underwater footage of sharks, Stewart joins renowned conservationist Paul Watson and the controversial Sea Shepard team aboard the Ocean Warrior. The team is invited and implored by the President of Costa Rica to help patrol the waters surrounding Cocos Island, one of the places celebrated as a gathering area for sharks, and where illegal shark fishing often takes place.
Complete with colliding ships, gunboat chases, espionage, corrupt courts, and spurious charges of attempted murder, the adventure that ensues is nothing short of epic.
Organized crime and conspiracy surrounding the shark fin industry is deeply entrenched. With dried fins sometimes fetching in excess of $400USD per pound, it is a multi-billion dollar industry rife with greed and corruption.
But it is more than corrupt government officials, or the “shark-fin mafia” that threaten Stewart’s life. Shortly after the entire crew must hurriedly flee from Costa Rica, Stewart is diagnosed with necrotizing fasciitis, the “flesh-eating” disease. Rare but deadly, the disease threatens to claim Stewart’s leg, and possibly his life. Alone, with only hope by his side, Stewart remains bedridden in a Panamanian hospital for an agonizing week before doctors can make any prognosis.
Determined more than ever to make a difference, Stewart defies reason and returns to Costa Rica. Knowing he would be arrested on sight, he and his crew must sneak back into the country. Ironically, when they arrive in Puntarenas, they are able to blend in — Protesters line the streets, demonstrating against shark finning and illegal shark fisheries. “Costa Ricans were rallying for sharks. . . I realized our adventure had helped awaken a country”, remarks Stewart with renewed faith.
Over the next four years, Stewart shot more than 400 hours of footage in 15 different countries. In addition to interviews with shark and conservation experts like Erich Ritter, Patrick Moore, and Rex Weyler, Sharkwater includes commentary from average beachgoers, showing how desperately fear and hate of sharks are ingrained. As one Australian angrily believes, “they’re the scourge of the ocean, and everyone should go and catch one.”
Sharks have been an integral part of the oceanic ecosystem for 400 million years, but their populations have declined by more than 90% in the last 50 years alone. It is estimated that more than 100 million sharks are killed for their fins each year.
Shark finning is neither humane nor sustainable. Any shark is taken, regardless of size, age, or species. After its fins are cut off, the shark is thrown back into the water. Unable to swim, and bleeding to death, the shark suffers a slow and torturous death.
Much of the demand for the fins stems from shark fin soup, a traditional asian dish often served at weddings and special events. Once a rare delicacy consumed by Chinese aristocracy, the dish is viewed as a symbol of status and power, and is gaining in popularity as China continues to modernize and its 1.2 billion people become more affluent.
Indeed, there is an uphill battle to be fought, but there is hope.
The Sharkwater crew interviews one Chinese bride who, defying long tradition and facing cultural stigma, makes a statement by refusing to serve shark fin soup at her wedding banquet. We can only hope that this — what is now seen as a controversial decision — will eventually become the norm.
With its spellbinding cinematography and riveting story, Sharkwater has won awards at every film festival where it has appeared. Sharkwater will change the way people view sharks and the ocean. It will open their eyes. . . and, hopefully, their hearts. You can create pet chrome emblems with Shark image to create awareness too.
Filed under Save Sharks · Tagged with addition, adventure, age, aim, Alone, area, aristocracy, Asia, asian, attempt, Australia, author, average, awaken, awareness, awe, ban, battle, beautiful sharks, blood, bloodthirsty, board, boat, camera, capture, car, care, Caribbean, caribbean reef shark, catch, chasm, China, claim, Co, Cocos Island, commentary, community, conservation, conservationist, conspiracy, Continue, contrary, corruption, Costa Rica, country, crew, crime, dangerous predators, death, decision, decline, delicacy, demand, Determined, difference, disease, dish, dog, Dollar, drama, ear, ecosystem, effort, epic, Erich Ritter, ESP, espionage, EST, everyone, excess, expert, eye, face, faith, fear, film, filmmaker, fin, fin soup, finished product, Finning, fins, fish, fisheries, fishing, flesh, foot, footage, forty years, gathering, Government, greed, gunboat, habitat, heart, hold, hospital, human drama, humane, ignorance, image, imagery, Important, industry, Join, killer, land, lapdog, laugh, leg, life, line, mafia, man eaters, matter, military training, million years, mind, murder, mystery, natural habitat, nothing, ocean, ocean warrior, official, Organized, part, Patrick Moore, patrol, Paul Watson, photographer, place, point, popularity, population, pound, power, precepts, predators, President, product, prognosis, project, Protesters, Puntarenas, rat, rate, reality, reason, Red, reef, relief, renowned conservationist, rest, Rex Weyler, Rob Stewart, round, row, scourge, sea, sea shepard, serv, shark, shark fin soup, Shark Finning, shark fish, shark fisheries, shark fishing, Sharks, SHARKWATER, Shepard, ship, shot, showing, side, sight, size, soup, Species, stand, status, Stewart, story, symbol, system, tag, team, Tens, term, thing, threat, time, training, truth, turn, understanding, underwater footage, underwater world, US, USD, use, video, video camera, Warrior, water, way, Week, With, world, year, Your