The teeth of a shark are disposable. The teeth are arranged in rows, and as the front row wears out, the back rows move forward to replace them. These replacements shift forward every few weeks.
Sharks are generally extremely adept at buoyancy control. They have very large livers that contain a large amount of oil, and this, along with their lightweight cartilage skeletons, helps them stay buoyant. Most sharks also stay in constant motion in order to keep water flowing through their gill slits, and this also helps them to stay afloat.
Most sharks are cold-blooded, but some species, such as the Mako and Porbeagle, are warm-blooded, which means they can control their own body temperatures. Some species are known to warm their body temperatures up to 10°C warmer than the temperature of the surrounding waters.
Sharks have a special sense called electrolocation, the ability to sense electrical signals in the water. Every living animal in the water emits electric signals around its body, which are called bioelectric potential. This bioelectric potential is even stronger around a cut in the flesh, and this puts an animal at higher visibility.While hunting, sharks hone in on electrical energy so that they can make a precise attack.
Electrolocation also helps sharks navigate over long distances, through multiple oceans and a diverse array of habitats. Sharks are known to travel up to 10,000 miles in straight lines while following magnetic fields, sometimes in the deep seas that provide no other navigational indicators (such as polarized light, wave cues, etc). Their sensitivity to electromagnetic fields is astounding. A shark can sense the electricity emitted by single battery in the sea from over a mile away!
Sharks have inhabited our seas for 450,000,000 years, since the time of the dinosaurs, but humans know comparatively little about them. Although many species have not been identified, there are currently over 450 known species of sharks.
The depletion of sharks changes the balance and risks the survival of whole ecosystems. As shark populations become decimated, the populations of other species thrive, throwing the slow-cooked, delicately balanced oceanic food web into a state of tumultuous upheaval that may take another 450,000,000 years to rebalance. In some areas, the decline of shark species due to overfishing has led to an overpopulation of rays, which in turn caused the collapse of scallop fisheries.
This great fear that humans have toward sharks is partly understandable. When out at sea, we are not in our natural element. Our limbs and feet are more suited to walking than swimming, and most of our senses work best on land. In a foreign environment, the fear of other species is heightened. As the Earth’s top land predator, human beings will always be fascinated by the idea of being preyed on by a larger animal. This psychological root is repeatedly played out in folklore and stories, from the Biblical tale of Jonah being swallowed by a whale to the novel, Moby Dick.
Such irresponsibly misleading media coverage reinforces the portrayal of sharks as indiscriminate killers. This reputation is further reinforced by news sources that sensationalize the rare shark attacks that do happen around the world. Pigs, vending machines, bee stings, and falling coconuts kill more humans per year than sharks, yet the media does not sensationalize these issues with such zeal because these dangers don’t rouse in us the delicious fear of the mysterious, insatiable, hostile archetype.
With such depictions in the cultural mindset, it’s easy to see why selachophobia, the irrational fear of sharks, is so common among humans. The majority of the human population will never get the opportunity to spend even a few minutes in the presence of one of these beautiful and elusive creatures in the wild (unless they seek out a biodiversity hotspot and fork up a lot of cash to go diving), but most people still cling to a fear of sharks. Despite how common and understandable this fear is, statistics assure us that this fear need not continue. Sharks are not as dangerous to human beings as many people think, and the chances of being attacked by a shark are infinitesimal. Worldwide, sharks are responsible for 4.2 human deaths on average per year. A person is 285,714 times more likely to die in a car accident and 16 times more likely to die from a bee sting than from a shark attack. Out of 400+ species of sharks, only a few species are “dangerous” to humans (white, tiger, and bull sharks account for over half of all shark attacks.
In reverse, experts estimate that humans kill up to 100,000,000 sharks each year. The irony of selachaphobia is that the chance of a shark being killed by a human is 30,000,000 times larger than the chance of a human being killed by a shark.
Peter Benchley, the writer of the book that the highly influential film, Jaws, was based on, regretted writing a book that demonized the great white shark. He spent his later life protecting sharks and promoting oceanic conservation.
There are various reasons for the rapid decline in shark populations: overfishing, destructive fishing practices, trophy hunting, habitat destruction, and shark finning.
Sharks are being overfished in many parts of the world at an alarming rate. Sharks are highly vulnerable to overfishing because they are generally slow growing and long-lived. Females reproduce late in life and have few offspring. With some sharks taking as long as 30 years to reach sexual maturity. This makes them inherently vulnerable to exploitation and slow to recover from population declines.
The nations with the highest shark catches are Indonesia and India, though much of their bounty is shipped to Hong Kong, which handles between 50-80% of the global shark fin trade. Shark products are used in fish fillets, supplements, cosmetics, leather, pet food, and even in the “fish” portion of fish and chips.
The most financially valuable part of the shark, and a primary incentive for shark fishing, is the fin. Large numbers of sharks become victims of the barbaric practice known as shark finning. In the practice of shark finning, a shark is caught, usually using a longline with baited hooks, and then pulled on board where fishermen cut the fins from the shark with no anaesthetic relief. Often still alive, the shark is thrown overboard and unable to swim and in agonizing pain, the shark then sinks to the bottom of the ocean to either drown or be eaten alive. This is not only a terribly cruel practice, but is also highly wasteful.
Global shark populations are being decimated to satisfy the persistent demand for shark fin soup. Shark fin soup is a symbol of wealth and is served at weddings, business dinners and important social engagements within Chinese communities worldwide. The fin trade is a multibillion-dollar industry, rivalled in revenue by illegal drugs and guns.
Sharks fins are popular based on health claims of scientifically unproven benefits. In fact, shark fin can be harmful; studies show that sharks contain among the highest levels of toxic mercury found in fish. Ingestion of mercury can lead to neurological and behavioural disorders, and can cause damage the kidneys and thyroid.
The global populations of this important apex predator are rapidly plummeting as you read this. It is imperative that the destructive practices that kill sharks come to their rightful end. Humans are merely one of the many species coexisting on Earth. We have no right to commit genocide on such a massive scale that it permanently alters the balance of our planet. Each of us must take the responsibility to educate ourselves so that we can avoid purchasing shark products. Now is a crucial time to declare shark sanctuaries and promote shark conservation worldwide before the rulers of the seas disappear forever.
What is overfishing?
Overfishing takes place when fish and other marine creatures are fished more quickly than they can reproduce and sustain their populations. To put it simply, taking too many fish out of the seas before new fish can be born to replace the ones that were caught.
What is so bad about overfishing?
Globally, 80 million metric tons of fish are caught annually, and if current trends continue, ocean ecosystems will be damaged irreversibly. Extracting too many fish from an ecosystem robs larger predator species of their food source and reduces their chances of survival. A depletion of one can put the whole food web at risk of collapse, and can lead to an overall degradation of an ecosystem. Worldwide, 90% of large predatory fish stocks are gone due to overfishing. The United Nations predicts that if current trends continue, global fish stocks will be extinct by the year 2048.
Some fisheries are completely depleted. The UN Food and Agriculture Organization (FAO) estimates that 90% of all fish stocks are either overexploited or fully exploited. The largest of bony fish, the Atlantic bluefin tuna, is heavily harvested for the global sushi market, to the point that its population has decreased by over 96% from unfished levels.
The depletion of fish stocks means a risk of losing a valuable food source that many depend upon for economical and dietary reasons. Nearly two-thirds of the world’s population relies on fish for 40% of their protein. About 13,000,000 people depend on fishing for all or major part of their incomes. People dependent on fishing for their livelihoods face resource depletion, competition from industrial fishing fleets, and loss of traditional lifestyles.
What causes overfishing?
The global demand for seafood is on the rise, and global marine catch has quadrupled since the 1960s. The response to meet this increased demand has been the emergence of overly efficient industrial fishing practices. These practices are wasteful, unsustainable, and destructive, leaving harm in their tracks. The environmentally devastating thing about these fishing methods is that they destroy other species, catch more than they need, catch fish that people don’t want to eat, and are non-selective in their target fish.
The bycatch that results from industrial fishing methods is devastating. Bycatch any the accidental catch outside of the targeted species. Sharks, whales, dolphins, marine turtles, and seabirds are regularly caught as bycatch. 25% of all fish pulled from the sea never make it to the market and are thrown overboard, dead or soon to be dead.
The use of fishing lines that can be up to 50 miles long, sometimes with baited hooks attached. These attract and kill non-targeted species such as sea turtles, sharks, and seabirds.
The use of a large net to encircle and catch groups of fish. This becomes a problem when non-targeted species are also ensnared or when too many fish are taken for the species to sustain their own populations.
A gillnet is a nearly invisible curtain of netting that floats at the surface or is anchored to the sea floor. Gillnets are commonly used to catch fish but produce large amounts of bycatch.
Trawls are nets that are towed at various depths. Trawl nets are huge and can result in high levels of bycatch. Some super trawler nets have openings that are the size of four soccer fields and can hold thirteen jumbo jets! As the heavy trawl nets are dragged along the ocean bed, they indiscriminately scoop up marine life and damage whole ecosystems. The damage trawling causes on the seafloor can be seen from outer space. Shrimp trawling creates disproportionate harm; shrimp accounts for 2% of all seafood caught, but bottom-trawling for shrimp produces 30% of the world’s bycatch.
FADs (Fish Aggregating Devices)
FADs are floating objects that are designed and strategically placed to attract pelagic fish. For centuries, fishermen have taken advantage many pelagic species’ tendency to associate with natural FADs in the open ocean, such as logs, seaweed, coconuts, and other debris. Man-made FADs are made from a variety of materials including ropes and lines that encourage the settlement of marine plants, small crustaceans and mollusks, which in turn attract small fish. In recent years however, advanced technology such as sonar- and GPS have enabled fishermen to electronically monitor FADs and know how many and at what depth the fish are located. These animals are then harvested with seines, hooks, or longlines. Such technological leaps have made commercial fishing operations extremely efficient at harvesting fish.
As coastal fish population decline, fishing fleets must travel further out into the deep seas, where larger fish reside. Nearly half of all trawling happens in 200m deep waters, which are further from the coast and often unregulated.
The most effective way you can shape your life into one that doesn’t impair the continuity of marine creatures is to stop buying or consuming seafood. This includes pet food, cosmetics, and supplements made from endangered or unsustainably caught marine creatures.
If you must eat seafood, consume species that are non-threatened and sustainably farmed or harvested. If you are buying seafood, it is your responsibility to inform yourself about sustainable, low-impact options. Every area has a unique situation, so find which of Monterey Bay Aquarium‘s Seafood Watch Guides covers your local area. Download the app or carry the pocket guide around in your wallet for easy use.
The quickly declining fish stocks are an urgent issue that demands immediate and serious action from both consumers and policy-makers. Only with a concerted effort and worldwide response can we ensure the vitality of marine species and wellbeing of the oceans.
In the coming 50 years, the Earth is expected to have temperatures and CO2 levels that are higher than those experienced in the past 500,000 years. Healthy oceans can act as a buffer for such rapid climate change; currently, oceans absorb nearly a third of all carbon emissions. In the past fifty years, the oceans have absorbed 90% of the heat caused by greenhouse gases. If this heat were to stay in the atmosphere, Earth’s ambient temperature would rise 3°C every decade.
Dr. James Hansen, the head of NASA’s Goddard Institute, predicts a sea level rise of 15 feet by the year 2100. A sea level rise of even three feet would bring about 100,000,000 climate refugees and would endanger London, Bangkok, Venice, New York, and Shanghai. Considering the fact that more than half the world’s population lives within 37 miles of a shoreline, this puts much of the global population at risk.
Land inundation is already happening. Saline-rich seawater has already flowed 35 miles up the Mekong’s riverbanks in Vietnam’s rice-growing region and is threatening 100,000 hectares of rice. 190 feet of coastline vanish each year in Rasheed, Egypt due to the encroachment of the sea. Bangladesh, often called the “ground zero of climate change”, already produces millions of climate refugees every year as the low-lying country is submerged. Sea level rise threatens 40 island nations with inundation, including the Maldives, Kiribati, and the Solomon Islands.
Most corals can revive themselves after short-term periods of bleaching, but the bleaching process limits their growth, makes them more vulnerable to the elements, and may cause death. In 1998, 16% of the world’s coral reefs perished due to bleaching. Studies in Asia’s oceans show that levels of coral bleaching in 2010 are at the peak since 1998 levels.
Throughout evolution, corals have been able to adapt to environmental changes, but the rapidity and extremity of current changes present a challenge to the adaptability of coral reefs. It is likely that in the next 50 years, CO2 levels in the atmosphere will double. Some believe that even the most optimistic speculations of future CO2 concentrations spell out a disastrous future for coral reefs.
This causes the calcification of species such as corals, mollusks, and crustaceans; their shells dissolve and they are inhibited them from forming new calcium carbonate. Coral reefs are the nurseries of the seas, and can shelter 1,000 species per square meter. The death of coral reefs affects food security, shoreline protection, marine biodiversity, and tourism.
Research also shows that elevated levels of CO2, acidification, and progressively warm temperatures encourage the growth of turf algae. Turf algae hinders the reproduction and growth of kelp forests, which are one of the most productive and valuable ecosystems on Earth.
It is understandable that some of us may never reach a zero-emission lifestyle due to societal structures and financial constraints, but the shameful fact that Americans emit more greenhouse gases per person than any other country should rouse Americans into taking steps to individually prevent further adverse effects and minimize CO2 levels. There are plenty of resources online that suggest ways in which one can reduce one’s carbon footprint. But if you take one thing from this article, it’s this: Drive less.
The largest cause of net increase in total U.S. greenhouse gas emissions is transportation. In 2013, transportation contributed approximately 27% of total U.S. greenhouse gas emissions.
Replace driving whenever possible with your legs, a bicycle, public transportation, or a skateboard. Each mile you do not drive prevents one pound of CO2 pollution. Habituate yourself into the massive behavior change and use transportation sources that reduce our dependence on fossil fuels.
The average American will throw away 185 pounds of plastic each year. And plastic never truly disappears. Every piece of plastic that has ever been made still exists. Even when burned, it breaks down into microscopic, toxic particles. Plastic is not a material that our planet can digest. Like diamonds, plastic is forever.
For example, when a plastic bottle is discarded improperly, rains and waterways may sweep it into a gutter and eventually out to sea. Floating at sea, the UV radiation of the sun makes the plastic brittle. The plastic breaks up into smaller pieces from the friction of the waves. In due course, the plastic breaks down into microplastic particles, which are fragments of plastic smaller than a grain of sand or the tip of a needle. Ocean currents sweep these microplastic particles to areas called gyres, where there are high concentrations of plastic.
Almost every marine organism is contaminated by plastic, from microscopic plankton to whales, the largest mammals on earth. Marine animals that become entangled in plastic may drown or starve. Plastic garbage may resemble food for some marine species. Turtles are known to mistake plastic bags for jellyfish. Sea birds selectively ingest specific colors of plastic, mistaking them for prey. Plastic is found in the stomachs of 85% of turtle species, 43% of seabird species, and 44% of marine mammals.
Eating plastic can hinder the secretion of gastric enzyme (which is needed for digestion) and cause the animal to starve.Other problems resulting from ingesting plastic are reproductive failure, lowered steroid levels, and delayed ovulation. Ingested plastic also introduces toxic pollutants, such as DDT and PCBs, into the animals’ bodies. The higher up the food chain a species is, the higher the amount of pollutants it will have. Thus, the bloodstreams and tissues of humans have very high levels of harmful chemicals leached by plastics. These chemicals are even found in newborns and in breast milk.
Eutrophication in the marine environment refers to the process during which the oceans receive surplus nutrients that encourage excessive plant growth. The runoff of fertilizers that are used in agriculture may cause phytoplankton and algae to grow in unusual and excessive numbers. These inordinately high populations of phytoplankton and algae reach the ends of their life cycles and settle onto the seabed as decomposing dead matter that consumes large amounts of oxygen during the decomposition process. The resulting lack of oxygen causes local marine animals to either suffocate or leave the area, and the lifeless area becomes a dead zone. There are now 400 dead zones globally, and this number is increasing exponentially.
Sound pollution is an invisible but noteworthy form of pollution in the oceans. As the oceans increasingly become used for the transport of goods, the sound environment of the oceans becomes noisier. The cacophonous environment jumbles or smothers the biosonar calls of marine animals that rely on sound for navigating, feeding, and communicating. Sonar, which is often used in military exercises, can hamper the biosonar calls of whales and may cause incorrect navigation and even stranding.
Factories, mining, chemical plants, and the burning of fossil fuels are among the causes of industrial contamination. The toxins and heavy metals resulting from these processes make their way into the oceans and are ingested by marine animals. Since many toxins are persistent, they build at increasing concentrations on their way up the food chain. For this reason, large predators such as sharks carry high levels of methyl mercury, a dangerous neurotoxin.
- Only purchase cosmetics and cleaning products that made of natural, non- toxic ingredients.
- Carry your own water bottle, mug, utensils, and reusable bag. Imagine a water bottle filled ¼ of the way with oil. That’s how much oil was used to make the bottle!
- Buy products that have the least amount of plastic packaging.
- Pick up plastic garbage when you see it. Plan a beach clean up for your community.
- Support organic produce or produce that is grown with non-toxic chemicals. Support companies that are environmentally conscious.
As the global population grows, coastal land use and development increases. With development come far-reaching impacts on coastal ecosystems and the species dependent on them. Coastal areas are home to over 90% of all marine species, and these habitats are being lost at an alarming speed. Coastal habitats include estuaries, marshes, mangrove ecosystems, sea grass, and coral reef. These habitats serve as nurseries, breeding grounds, feeding spots, and the destruction of these habitats afflict repercussions to dependent species. An altered population structure of a species causes a domino effect throughout the whole chain web. And habitats don’t exist in isolation; most of them have inputs and outputs to other habitats that are, in turn, set off balance as well.
Escalating pressures to develop coastlines for industrial purposes are increasing the rate of habitat destruction. Some causes are poorly designed development projects for residential or and commercial establishments; shipping port construction; shipping operations such as dredging, levees, and breakwater structures; chemical runoff; oil and gas related activities, water pollution, and the alteration of freshwater inflows. Spills of crude oil change the population distribution of, or even kill, hundreds of marine species and leave a toxic environment that can persist for years. Oil sediment has been detected as much as thirty years after an oil spill. The Rena oil spill in the Bay of Plenty, New Zealand killed an estimated 20,000 sea birds.
Another major ecological impact derives from the sediment remains of logging. When sediment loads enter the sea, it limits the penetration of the sunlight that primary and secondary producers need, thus modifies the whole food web. The sediment also smothers coral reefs and threatens dependent marine life. Coral reefs are critical, as they make up less than 1% of the ocean’s surface, but are home to 25% of all marine life.
Nature Tourism and Recreation
As travel becomes cheaper and more widespread, nature tourism and recreation become a persistent cause of disturbance to coastal ecosystems. Tourism brings millions of scuba divers, snorkelers, kite surfers, and bird watchers into direct contact with reefs, wetlands, and mangrove forests. Well-meaning nature enthusiasts may unknowingly damage habitats with their boat anchors, fishing gear, and improper diving or snorkelling practices.
Agriculture is a necessity for human sustenance that has unfortunate effects on coastal habitats. Fertilizer, sewage, and soil runoff are a direct cause of eutrophication. During this process, the excess nutrients from runoff, rich in nitrogen and phosphorus, stimulate growth of algae in what is called an “algal bloom”. Algal blooms block sunlight and deplete the water and reefs of oxygen, which is required by the zooxanthellae in coral to photosynthesize and remain alive. Almost 600 square miles of reef have disappeared every year since the 1960s. This means the reefs are disappearing twice as quickly as tropical rainforest are.
Aquaculture – fish and shellfish farming – are responsible for severe declines of productive ecosystems. Aquaculture may alter natural drainage patterns, increase salinity, or pollute coastal waters with pollutants and sediments.
An ecosystem that has been significantly disturbed by aquaculture is the mangrove forest. Commercial shrimp farming is responsible for 25% of all mangrove destruction!
As habitats disappear, not only marine species but also human communities suffer from the loss of resources. Healthy mangrove forests provide a habitat and nursery for fish species, filter salt water, collect sediment and protect erosion, and act as a buffer zone and protection from the impacts of storms and floods. In the past decades, 35% of all mangrove forests have vanished. Such a drastic loss spells out an increased exposure to natural forces.
- Support and donate to the creation of marine parks, biosphere reserves, and Marine Protected Areas, where development is limited and fishing is prohibited.
- Be a conscious consumer. Buy organic produce grown without pesticides, fertilizers, and other toxic chemicals. Carry a sustainable seafood guide so you can choose seafood obtained with nondestructive methods.
- Support legislation that bans the dumping of sewage and chemicals into the oceans.
- Be an ecologically respectful tourist by educating yourself on the impact your mode of recreation may have on local ecosystems. Ask your dive shop, tour guide, or tour boat what steps they take to insure a no-impact experience.
The growing impact of human activities is causing a rapid loss of animal and plant biodiversity. Currently, the rate of animal extinction is 1,000 to 10,000 times higher than the natural extinction rate. According to a UN report on the state of the global environment, 25% of the world’s mammals face extinction by the year 2032. Some scientists predict that the world is about to face the sixth mass extinction. A mass extinction, in the paleontological sense, is diagnosed when the pace of extinction is significantly higher than the pace of origination. Over the past 540 million years, five mass extinctions have occurred, during which at least 75% of all animal species were destroyed due to natural causes. However, the threat of extinction today is caused by manmade influences including habitat loss, overhunting, overfishing, the spread of invasive species and viruses, pollution, and the frighteningly high expansion rate of the human population.
In the oceans, the rate of biodiversity destruction is cataclysmic. The endangerment of whale, dolphin, manatee, tuna, sea turtle, and shark species are on the rise. UNESCO reports claim that if significant changes are not implemented, more than half of all marine species may stand on the brink of extinction. Marine species, both live and dead, have significant financial value in the global market, however, and aside from ecotourism, these species are rarely attributed financial value in their natural environments. The financial benefits of catching and exploiting marine resources are a driving factor of the global marine trade. An estimated 50-80% of all life on Earth is found under the surface of the seas; the loss of marine life is not to be taken lightly.
There is a wide range of causes of marine species extinction and endangerment, such as habitat loss, acidification, atmospheric change, and pollution. The most dominant and influential threat, however, is overfishing. Overfishing is reported to be the greatest threat to marine biodiversity in all regions. Fish populations plummeted fastest during the initial years of commercial fishing, often before population drops were calculated. By now, the loss of fish stocks is conspicuous. A global study concludes that 90% of all large fish have disappeared from the oceans since 1960 as a result of industrial fishing practices such as long lining, bottom trawling, and dredging. The commercial fisheries have caused an overexploitation of fish stocks so severe that 13% of global fisheries have collapsed. The continued use of destructive fishing operations delays ecosystem and population recovery, and may even prevent it completely.
When the population of a species is reduced, the genetic variation is reduced along with it. This compromises the species’ ability to adapt to new environmental stresses and changes. Due to the interdependencies between species, the destruction of one can lead to the demise of others. When whole species are wiped out or remain at insignificant population levels, the stability of the whole ecosystem is under threat.
- Support the creation and maintenance of marine protected areas (MPAs), nature reserves, and national parks. Public foundations or state and federal governments are often responsible for the management of parks and reserves. Let these know that you advocate nature reserves, MPAs, and national parks. When visiting a protected area, obey the wildlife code. Follow fire regulations and don’t take anything away that you didn’t bring in.
- Volunteer with an organization that protects or replants threatened species in your area. By replanting native bush, flowers, and trees, you are encouraging native animals to return and are providing them with more space in which to live.
- Get your voice heard through websites, radio stations, newspapers, and publications. Talk about threatened species and what we can do to help preserve them and their habitats.