Seafood is any form of sea life regarded as food by humans, prominently including fish and shellfish. Shellfish include various species of molluscs e. Historically, marine mammals such as cetaceans whales and dolphins as well as seals have been eaten as food, though that happens to a lesser extent in modern times. Edible sea plants such as some seaweeds and microalgae are widely eaten as sea vegetables around the world, especially in Asia.
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Smithsonian OceanVIDEO ON THE TOPIC: 11 Scariest Ocean Predators
A 1 , Haque. ASM 2 , Hossain. Before going to the definition of overfishing we need to know the Definition of bycatch. After a catch is hauled aboard, the non-commercial marine life, is culled out and thrown back, known as "bycatch". Bycatch is not limited to unwanted fish species. Bycatch can be fish with no commercial value, juveniles of marketable species, all types of marine life including whales, dolphins, porpoises, fur seals, albatrosses and turtles are killed as bycatch.
For example, a staggering million sharks are killed each year. Tuna fisheries, which in the past had high dolphin bycatch levels, are still responsible for the deaths of 1 million sharks.
And Discards are animal returned to the sea after being caught. Overfishing can be defined as the catching of more fish from a single population than can be naturally replaced on an annual basis. Fishing with a sufficiently high intensity to reduce the breeding stock levels to such an extent that they will no longer suppport a sufficient quantity of fish for sport or commercial harvest.
The harvesting of a particular species of fish to the point where it can no longer reproduce itself in large numbers in a given area. In other words, catching too many fish; fishing so much that the fish cannot sustain their population.
The fish get fewer and fewer, until finally there are none to catch. If we know how often a female produces eggs, how many eggs she produces each time, and how many years she is likely to live, we can calculate how many eggs she would produce over her life time.
According to the Magnuson-Stevens Fishery Conservation and Management Act as a rate or level of fishing mortality that jeopardizes the capacity of a fishery to produce the maximum sustainable yield on a continuing basis. Overfishing pushed many commercially important fish populations into steep declines for example Canada's northern cod.
Some commercially important stocks are in such a critical state that all fishing has been shut down, or sharply curtailed. There are various causes of overfishing, such as:. The rapid increase in demand for fish and fishery products leading to increase fish price faster than prices of meat:.
During past few decades, the large increase of demand especially for marine fish and marine fishery products leading to increase fish price faster than prices of meat. Fish prices are increasing that encourages people to do fishing because of high technology, high price and high profit.
As a result, fisheries investments have become more attractive to both entrepreneurs and governments, much to the detriment of small-scale fishing and fishing communities all over the world. Some are even recommending zero catches to allow for regeneration of stocks. Hence day by day the demand for fish products is increasing remarkably and it leads to overfishing.
Rapid advance of fishing technology:. Most of the problems associated with overfishing have been caused in the last 50 years by the rapid advances in fishing technology. The fishing vessels are replaced by huge factory ships which are able to stay out at sea for weeks at a time.
These factory boats have all the equipment necessary either to freeze or tin fish caught by their hunting ships, so that they need to return to base only when their holds are full. As catches have gradually become smaller, so the mesh sizes used in fishing nets have decreased, allowing smaller and smaller fish to be caught. Many of these are too small to be used as food, so they are crushed to be made into either animal food or fertilizer.
The dramatic increase of use of destructive fishing techniques and gear :. The dramatic increase of use of destructive fishing techniques and gear worldwide destroys fisheries, marine mammals and entire ecosystems.
Along with the growing fleet come more fishing nets in the water, some of which are very non selective. It is impossible to catch only the desired fish species, this harvest of non-target species is called bycatch.
Bycatch constitute all of the animals that are caught but not wanted or used or are required to be discarded by management regulation Somma This includes endangered or protected species, fish that are legally to small to catch, or those that have to commercial value. It is estimated that bycatch makes up a quarter of all the fish caught, but most of the bycatch are dead before being thrown back to the water.
Equipment such as purse seine nets, longlines, gillnets and trawls are especially harmful to the environment. They tend to catch juvenile fish, birds and other nontarget animals. Gill nets are also dangerous as many are discarded in the water, yet continue to kill fish in what is known as ghost fishing. Trawls are especially dangerous, they produce significant bycatch while damaging the environment as they are dragged along the seafloor.
Using smaller mesh size net :. Fishing using nets is indiscriminate. Any fish which get in the way of the net will be caught in it if they are too big to get through the mesh. For every one tonne of prawns caught, three tonnes of other fish are killed and thrown away. Some sea fish live in the upper parts of the water. They are called 'pelagic' fish, and are caught by drift netting. This is where a net suspended from floats is stretched between two boats so that fish swim into it.
Fish are unable to swim backwards, so once they are caught in the net, there is no escape unless they are small enough to fit through the net's mesh. More time, effort and money in fishery sector:.
Open access to fishing in most fisheries and Non enforcement of modern management regulations:. In the past 25 years, the worldwide number of fishermen has more than doubled. In most developing countries, the poor have no choice but "to glean the last of the resource". Free and open access encourages overfishing as fishermen tend to catch as much fish as they can without taking care to maintain the fish stock.
The common property nature of the fishery resources, resulting in unregulated access to many of the resources. FAO reports that due to the common property nature of the fishery resources, resulting in unregulated access to many of the resources illegal, unreported and unregulated fishing worldwide appears to be increasing as fishermen seek to avoid stricter rules in many places in response to shrinking catches and declining fish stocks.
Subsidies from governments to the fishing industry :. Today, there isn't a fishing region in the world that does not suffer from fisheries management decisions designed to satisfy short - term economic or political objectives or both rather than protecting the marine environment and conserving fish populations.
Indeed, in many countries, governments have played an important part in fueling the expansion of excessive fishing capacity and overexploitation by providing lucrative subsidies, taxpayer funded handouts. The European Union spends a large amount of money on what many would describe as a dying industry.
Indeed there is a valid argument that fishing in the EU should be left to die. However the political fallout from this would be immense. Fisheries subsidies sometimes provide jobs in poor coastal regions and help countries expand their fishing industry. However, most of the time, the same subsidies encourage companies to develop high-tech fishing and thus overfishing. Growth overfishing:.
Growth overfishing occurs when animals are harvested at an average size that is smaller than the size that would produce the maximum yield per recruit. The total yield from the fishery is therefore less than it would be if the fishing mortality rate, or percent of the stock removed each year, was lower.
In such a case, less fishing would produce higher landings. Growth overfishing still reduces the potential yield from a fishery, and thus the economic and other benefits that could be obtained from the stock. For example : Heavy fishing removes the larger animals and does not give young lobsters a chance to grow to their potential size. Most of the large lobsters in the inshore fishery were caught during the s and early s.
Lower fishing pressure on the offshore lobster stocks allows more lobsters to grow to a larger size, but even there the size range is much reduced from the early days of the fishery. Recruitment overfishing :. The rate of fishing above which the recruitment to the exploitable stock becomes significantly reduced. This is characterized by a greatly reduced spawning stock, a decreasing proportion of older fish in the catch, and generally very low recruitment year after year.
Recruitment refers to the time when young fish become big enough to be caught. Recruitment overfishing means so many adults have been caught that there are no longer enough young adults to maintain the population. When fishing pressure is too heavy to allow a fish population to replace itself.
Occurs in circumstances where an increase in fishing effort from current levels will cause a decline in recruitment to a fishery. Recruitment overfishing can be brought about by:. Instead the crucial aspect is that the spawning stock should be large enough to ensure that the subsequent recruitment remains independent of the parental stock.
Ecosystem Overfishing :. Occurs when the species composition and dominance of an ecosystem is significantly modified by fishing, e. Competition and predation between taxa. It may be described here as what takes place in a mixed fisheries when the decline through fishing of the originally abundant stocks is not fully compensated for by the contemporary or subsequent increase of the biomass of other exploitable animals.
Overfishing is the biggest threat to the ocean environment. Concern for biodiversity stems finding that overfishing of higher-trophic-level fish stocks i. One characteristic of overfished ecosystems is sequential depletion of economic stocks Orensanz et al. Switching between target species occurs when resources of economic importance are markedly reduced in abundance by overfishing and when there are other more abundant stocks available.
Piscivores and valuable invertebrate stocks are particularly vulnerable to this fishing pattern Christensen, ; Oresanz et al. Overfishing and depletion of some stocks may become so severe that they may be regarded as economically extinct. The symptoms of ecosystem overfishing include: reductions in diversity; reductions in aggregate production of exploitable resources; decline in mean trophic level, increased by-catch; greater variability in abundance of species; greater anthropogenic habitat modification Hall, ; and, in extreme cases, change to alternative stable species regimes Steele, Economic overfishing :.
A level of fish harvesting that is higher than that of economic efficiency; harvesting more fish than necessary to have maximum profits for the fishery occurs when the costs of fishing effort are greater than the revenue generated from fishing: Incomes of fishermen continuously decline.
Note that this optimum level of effort is always less than that required to extract maximum sustainable yied MSY and that, therefore, maximum economic yield is always less than MSY. The stated or implicit goals of many management schemes; and that beyond MSY, subsidies will reduce catches by reducing total cost.
The combination of growth and recruitment overfishing leading to catch decline on the right, descending side of surplus production models Schaefer , ; Fox ; Ricker Catching such a high proportion of one or all age classes in a fishery as to reduce yields and drive stock biomass, and spawning potential below safe levels.
Marine Biology. August , Cite as. Understanding the energy flux through food webs is important for estimating the capacity of marine ecosystems to support stocks of living resources. The energy density of species involved in trophic energy transfer has been measured in a large number of small studies, scattered over a year publication record. Here, we reviewed energy density records of Southern Ocean zooplankton, nekton and several benthic taxa, including previously unpublished data.
Southern Resident Killer Whales
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Aquatic food webs
The following information was supplied regarding data availability:. The raw data from the sperm whale stomach contents are available in Table S1. Despite numerous studies across the large geographic range of the sperm whale Physeter macrocephalus , little is known about the diet and mitochondrial DNA haplotypes of this strongly female philopatric species in waters off Southeast Asia. A female sperm whale found dead in Singapore waters provided the opportunity to study her diet and mitochondrial DNA haplotype. Here we report on the identification of stomach contents and mitochondrial DNA haplotype of this individual, and we include coastal hydrodynamic modelling to determine the possible geographic origin of the whale. At least 28 species of prey were eaten by this adult female whale, most of which were cephalopods.SEE VIDEO BY TOPIC: Whales and Orcas Feeding Together - BBC Earth
A 1 , Haque. ASM 2 , Hossain. Before going to the definition of overfishing we need to know the Definition of bycatch. After a catch is hauled aboard, the non-commercial marine life, is culled out and thrown back, known as "bycatch". Bycatch is not limited to unwanted fish species. Bycatch can be fish with no commercial value, juveniles of marketable species, all types of marine life including whales, dolphins, porpoises, fur seals, albatrosses and turtles are killed as bycatch. For example, a staggering million sharks are killed each year. Tuna fisheries, which in the past had high dolphin bycatch levels, are still responsible for the deaths of 1 million sharks. And Discards are animal returned to the sea after being caught.
35 Utterly Weird Sea Animals
All rights reserved. The lowly krill averages only about two inches in length, but it represents a giant-sized link in the global food chain. They in turn are the main staple in the diets of literally hundreds of different animals, from fish, to birds, to baleen whales. Pink and opaque, Antarctic krill Euphausia superba are among the largest of the 85 known krill species.
Contains many misstatements of facts and distortions, in particular statements of glaciers retreating at a rate such that they will be gone by This was proven to be an error. This is the definitive source for information on the likely impacts of climate change, circa As with all IPCC assessment reports, only 'established science' can be included, which means that the latest scientific results are generally not included this policy has advantages and disadvantages, the primary advantage is that the science presented in IPCC reports is unlikely to be contested or refuted by later research. Account Options Sign in. My library Help Advanced Book Search. Get print book. Cambridge University Press Amazon. Shop for Books on Google Play Browse the world's largest eBookstore and start reading today on the web, tablet, phone, or ereader.
All About the Ocean
Yet when most people think of these cartilaginous fish, a single image comes to mind: a large, sharp-toothed and scary beast. That generalization does sharks a huge disservice, as they have far more variety than that. They range in size from the length of a human hand to more than 39 feet 12 meters long; half of all shark species are less than one meter or about 3 feet long. They come in a variety of colors including bubble gum pink , and some feed on tiny plankton while others prefer larger fish and squids. They are found in just about every kind of ocean habitat, including the deep sea, open ocean, coral reefs, and under the Arctic ice. Sharks and their relatives were the first vertebrate predators, and their prowess, honed over millions of years of evolution, allows them to hunt as top predators and keep ecosystems in balance. But sharks are in trouble around the world. Rising demand for shark fins to make shark fin soup, an Asian delicacy, has resulted in increased shark fishing worldwide; an estimated million sharks are killed by fisheries every year. Sharks are accidentally caught in nets or on long line fishing gear.
Commercial fishing , the taking of fish and other seafood and resources from oceans, rivers, and lakes for the purpose of marketing them. In the early 21st century about million people were directly employed by the commercial fishing industry, and an estimated one billion people depended on fish as their primary source of animal protein. Fishing is one of the oldest employments of humankind. Ancient heaps of discarded mollusk shells, some from prehistoric times, have been found in coastal areas throughout the world, including those of China, Japan, Peru, Brazil, Portugal, and Denmark. Archaeological evidence shows that humans next learned to catch fish in traps and nets. These ventures were limited at first to the lakes and rivers, but as boats and fishing devices were improved, humans ventured into sheltered coastal areas and river mouths and eventually farther out onto the continental shelves, the relatively shallow ocean plains between the land and the deeper ocean areas. In some shelf areas where seaweed was abundant, this was also incorporated into the diet. Fishing technology continued to develop throughout history, employing improved and larger ships, more sophisticated fishing equipment, and various food preservation methods. Commercial fishing is now carried on in all types of waters, in all parts of the world, except where impeded by depth or dangerous currents or prohibited by law.
Friday, January 21, The ocean covers 70 percent of the Earth 's surface. It contains about 1. The ocean makes all life on Earth possible, and makes the planet appear blue when viewed from space.
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We begin with the welcome sight of Sir David perched at the bow of a ship, who tells us that our oceans are changing at a faster rate than ever before. Blue Planet II has come at just the right time, as showing viewers the beautiful fragility of these ecosystems on a worldwide platform is the first step towards engaging everyone in conservation. The first scene that takes place beneath the waves sees a family of bottlenose dolphins rubbing themselves against the fronds of a Gorgonian coral, a species which is thought to possess anti-microbial and anti-inflammatory properties. In fact, the bottlenose dolphin possesses the second-largest brain-to-body-weight ratio of any animal, behind only humans.
Marine mammals are a food source in many countries around the world. Historically, they were hunted by coastal people, and in the case of aboriginal whaling , still are.