A fishery is an area with an associated fish or aquatic population which is harvested for its commercial value. Fisheries can be wild or farmed. Most of the world's wild fisheries are in the ocean. This article is an overview of ocean fisheries.
Statistics
Oceans occupy 71 percent of the Earth's surface. They are divided into five major oceans, which in decreasing order of size are: the Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern Ocean, and Arctic Ocean. Over 70 percent of the world catch from the sea comes from the Pacific Ocean.
The Pacific Ocean is the largest of the world's oceans, extending from the Arctic in the north to Antarctica in the south. Covering 169.2 million square kilometers, it is larger than all of the Earth's land area combined.[9]
The Pacific contains 25,000 islands (over half the islands in the world), most of which are south of the equator.
The Celebes Sea has warm clear waters and harbors about 580 of the world's 793 species of reef-building corals, which grow as some of the most bio-diverse coral reefs in the world, and an impressive array of marine life, including whales and dolphins, sea turtles, manta rays, eagle rays, barracuda, marlin and other reef and pelagic species. Tuna and yellow fin tuna are also abundant. The sea also yields other aquatic products like sea tang.
A map of the Coral Sea Islands.
The Coral Sea is an ecologically important source of coral.[10]
The Sea of Japan. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure.[11] It has an area of 978,000 square kilometre, a mean depth of 1,753 meters, and a maximum depth of 3,742 meters.
The areas in the north and the southeast are rich fishing grounds. The importance of the fishery in the sea is well illustrated by the dispute between South Korea and Japan over Liancourt Rocks.
The South China Sea is the repository of large sediment volumes delivered by the Mekong River, Red River and Pearl River. Within the sea, there are over 200 identified islands and reefs, including a 100 km wide seamount with a depth of 20 m and an area of 8,866 km2. According to studies made by the Department of Environment and Natural Resources, Philippines, this body of water holds one third of the all world's marine biodiversity, thereby making it a very important area for the ecosystem.
The Atlantic Ocean is the second-largest ocean covering 106.4 million square kilometres with a coastline of 111,000 kilometres. It occupies about one-fifth of the Earth's surface.
The ocean has some of the world's richest fishing resources, especially in the waters covering the shelves. The major species of fish caught are cod, haddock, hake, herring, and mackerel. The most productive areas include the Grand Banks of Newfoundland, the shelf area off Nova Scotia, Georges Bank off Cape Cod, the Bahama Banks, the waters around Iceland, the Irish Sea, the Dogger Bank of the North Sea, and the Falkland Banks. Eel, lobster, and whales have also been taken in great quantities. Because of the threats to the ocean environment presented by oil spills, marine debris, and the incineration of toxic wastes at sea, various international treaties exist to reduce some forms of pollution.
The Baltic Sea. Approximately 100,000 km2 of the Baltic's seafloor (a quarter of its total area) is a variable dead zone. The more saline (and therefore denser) water remains on the bottom, isolating it from surface waters and the atmosphere. This leads to decreased oxygen concentrations within the zone. It is mainly bacteria that grow in it, digesting organic material and releasing hydrogen sulfide. Because of this large anaerobic zone, the seafloor ecology differs from that of the neighbouring Atlantic.
The low salinity of the Baltic sea has led to the evolution of many slightly divergent species, such as the Baltic Sea herring, which is a smaller variant of the Atlantic herring. The benthic fauna consists mainly of Monoporeia affinis, which is originally a freshwater species. The lack of tides has affected the marine species as compared with the Atlantic.
The Caribbean Sea is home to about 29% of the world's coral reefs. Currently, unusually warm Caribbean waters are endangering the Caribbean coral reefs. Coral reefs support some of the most diverse habitats in the world, but are fragile ecosystems. When tropical waters exceed 85 degrees Fahrenheit for an extended period of time, microscopic plants called zooxanthellae die off. These plant provide food for the coral and give them their color. The resultant bleaching of the coral reefs kills them, and ruins the ecosystem. Up to 42% of the coral colonies have gone completely white, while 95% have undergone at least some bleaching.[12] The habitats supported by the reefs are critical to such tourist activities such as fishing and diving, and provide an annual economic value to Caribbean nations of $3.1-$4.6 billion. Continued destruction of the reefs could severely damage the region's economy.[13] A Protocol of the Convention for the Protection and Development of the Marine Environment of the Wider Caribbean Region came in effect in 1986 to protect the various endangered marine life of the Caribbean through forbidding human activities that would advance the continued destruction of such marine life in various areas. Currently this protocol has been ratified by 15 countries.[14]
The area also generates a large fishing industry for the surrounding countries, accounting for half a million metric tons of fish a year.[15]
The Gulf of Mexico. The outer margins of the wide continental shelves of Yucatán and Florida receive cooler, nutrient-enriched waters from the deep by a process known as upwelling, which stimulates plankton growth in the euphotic zone. This attracts fish, shrimp, and squid.[16] River drainage and atmospheric fallout from industrial coastal cities also provide nutrients to the coastal zone.
The Gulf Stream, a warm Atlantic Ocean current and one of the strongest ocean currents known, originates in the gulf, as a continuation of the Caribbean Current-Yucatán Current-Loop Current system. Other circulation features include the anticyclonic gyres which are shed by the Loop Current and travel westward where they eventually dissipate, and a permanent cyclonic gyre in the Bay of Campeche. The Bay of Campeche in Mexico constitutes a major arm of the Gulf of Mexico. Additionally, the gulf's shoreline is fringed by numerous bays and smaller inlets. A number of rivers empty into the gulf, most notably the Mississippi River in the northern gulf, and the Grijalva and Usumacinta Rivers in the southern gulf. The land that forms the gulf's coast, including many long, narrow barrier islands, is almost uniformly low-lying and is characterized by marshes and swamps as well as stretches of sandy beach.
The Mediterranean Sea. Being nearly landlocked affects the Mediterranean Sea's properties; for instance, tides are very limited as a result of the narrow connection with the Atlantic Ocean. Evaporation greatly exceeds precipitation and river runoff in the Mediterranean, a fact that is central to the water circulation within the basin.[17] Evaporation is especially high in its eastern half, causing the water level to decrease and salinity to increase eastward.[18] This pressure gradient pushes relatively cool, low-salinity water from the Atlantic across the basin; it warms and becomes saltier as it travels east, then sinks in the region of the Levant and circulates westward, to spill over the Strait of Gibraltar.[19] Thus, seawater flow is eastward in the Strait's surface waters, and westward below; once in the Atlantic, this chemically-distinct "Mediterranean Intermediate Water" can persist thousands of kilometers away from its source.[20]
The Mediterranean Sea has an average depth of 1,500 metres (4,920 ft) and the deepest recorded point is 5,267 meters (about 3.27 miles). The coastline extends for 46,000 kilometres (29,000 mi).
Invasive species originating from the Red Sea and introduced into the Mediterranean by the construction of the Suez canal have become a major component of the Mediterranean ecosystem and have serious impacts on the Mediterranean ecology, endangering many local and endemic Mediterranean species. Up to this day, about 300 species native to the Red Sea have already been identified in the Mediterranean Sea, and there are probably others yet unidentified. In recent years, the Egyptian government's announcement of its intentions to deepen and widen the canal have raised concerns from marine biologists, fearing that such an act will only worsen the invasion of Red Sea species into the Mediterranean, facilitating the crossing of the canal for yet additional species.[21]
Pollution in this region has been extremely high in recent years. The United Nations Environment Programme has estimated that 650 million tons of sewage, 129,000 tons of mineral oil, 60,000 tons of mercury, 3,800 tons of lead and 36,000 tons of phosphates are dumped into the Mediterranean each year.[22] The Barcelona Convention aims to 'reduce pollution in the Mediterranean Sea and protect and improve the marine environment in the area, thereby contributing to its sustainable development.'[23]
The Mediterranean is also plagued by marine debris. A 1994 study of the seabed using trawl nets around the coasts of Spain, France and Italy reported a particularly high mean concentration of debris; an average of 1,935 items per square kilometre. Plastic debris accounted for 76%, of which 94% was plastic bags.[25]
The North Sea. A large part of the European drainage basin empties into the North Sea including water from the Baltic Sea. Fishing in the North Sea is concentrated in the southern part of the coastal waters. The main method of fishing is trawling. Annual catches grew each year until the 1980s, when a high point of more than 3 million metric tons (3.3 million S/T) was reached. Since then, the numbers have fallen back to around 2.3 million tons (2.5 million S/T) annually with considerable differences between years. Besides the fish caught, it is estimated that 150,000 metric tons (165,000 S/T) of unmarketable by-catch are caught and around 85,000 metric tons (94,000 S/T) of dead and injured invertebrates.[26]
The Norwegian Sea. In the Norwegian Sea and Greenland Sea, surface water descends two to three kilometres down to the bottom of the ocean, forming cold, oxygen-rich groundwater. As a result, there is a warm surface current and a cold depth current running along the west coast of Norway. The so-called East Iceland Current transports cold water south from the Norwegian Sea towards Iceland and then east, along the Arctic Circle. In the Norwegian Current, a branch of the Gulf Stream carries warm water masses northward and contributes to the mild and moist climate in Norway. The Norwegian Sea is the source of much of the North Atlantic Deep Water. The region remains ice-free due to the warm and saline Norwegian Atlantic Current. It provides rich fishing grounds, with catches mostly consisting of cod, herrings, sardines and anchovies. Nowadays, shifts and fluctuations in these currents are closely monitored, as they are thought to be indicators for an ongoing climate change.
The Indian Ocean is the third largest ocean, covering 73,556,000 square kilometres, or about twenty percent of the water on the Earth's surface. Small islands dot the continental rims.
The ocean's continental shelves are narrow, averaging 200 kilometres (120 mi) in width. An exception is found off Australia's western coast, where the shelf width exceeds 1,000 kilometres (620 mi). The average depth of the ocean is 3,890 metres (12,760 feet). The remaining 14% is layered with terrigenous sediments. Glacial outwash dominates the extreme southern latitudes.
The warmth of the Indian Ocean keeps phytoplankton production low, except along the northern fringes and in a few scattered spots elsewhere; life in the ocean is thus limited. Fishing is confined to subsistence levels. Its fish are of great and growing importance to the bordering countries for domestic consumption and export. Fishing fleets from Russia, Japan, South Korea, and Taiwan also exploit the Indian Ocean, mainly for shrimp and tuna. Endangered marine species include the dugong, seals, turtles, and whales. Oil and ship pollution threatens the Arabian Sea, Persian Gulf, and Red Sea.
The Andaman Sea is a body of water to the southeast of the Bay of Bengal, south of Myanmar, west of Thailand and east of the Andaman Islands; it is part of the Indian Ocean. It is roughly 1,200 kilometres (750 mi) long (north-south) and 650 kilometres (400 mi) wide (east-west), with an area of 797,700 square kilometres (308,000 sq mi). Its average depth is 870 meters (2,854 ft), and the maximum depth is 3,777 meters (12,392 ft).
Kerilia jerdonii is a sea snake of the Bay of Bengal. Glory of Bengal cone (Conus bengalensis) is just one of the seashells which can be photographed along beaches of the Bay of Bengal.[27]
The Great Australian Bight is a large bight, or open bay located off the central and western portions of the southern coastline of mainland Australia.
The coast line of the Great Australian Bight is characterised by stunning cliff faces (up to 60 m high), surfing beaches and rock platforms, ideal for whale-watching. The waters of the Great Australian Bight, despite being relatively shallow, are not fertile. While most continental shelves are rich in sea life and make popular fishing areas, the barren deserts north of the bight have very little rainfall, and what there is mostly flows inland, to dissipate underground or in salt lakes. In consequence, the Great Australian Bight receives very little of the runoff that fertilises most continental shelves and is essentially a marine desert. It is probably best noted for the large number of sharks that frequent its coastal waters, as well as the increasing numbers of southern right whales that migrate within the region.
Economically, the Bight has been exploited over many years as part of the fishing, whaling and shellfish industries. Bluefin tuna have been a favoured target of fishing in the Bight.
The Gulf of Aden. The temperature of the gulf varies between 15 °C (59 °F) and 28 °C (82 °F), depending on the season and the appearance of monsoons. The salinity of the Gulf at 10 metres (33 ft) depth varies from 35.3 ‰ along the eastern Somali coast to as high as 37.3 ‰ in the Gulf's center,[30] while the oxygen content in the Gulf of Aden at the same depth is typically between 4.0 and 5.0 mL/L.[30]
A geologically young body of water, the Gulf of Aden has a unique biodiversity that contains many varieties of fish, coral, seabirds, and invertebrates. This rich ecological diversity has benefitted from the relative lack of pollution during the history of human habitation around the Gulf, but environmental groups fear that the lack of a coordinated effort to control pollution may jeopardize the Gulf's ecosphere.[31]
The Gulf of Aden is an area known for acts of piracy,[32]|-
The Mozambique Channel is a portion of the Indian Ocean between the island of Madagascar and southeast Africa, namely Mozambique. The channel is approximately 460 kilometers across at its narrowest point between Angoche, Mozambique, and Tambohorano, Madagascar. It reaches a depth of 3,292 meters about 230 kilometers off the coast of Mozambique. A warm current flows in a southward direction in the channel, leading into the Agulhas Current off the east coast of South Africa. It is 1600 kilometers long and its width varies from 400 to 950 kilometers.
The Persian Gulf is an extension of the Indian Ocean located between Iran and the Arabian Peninsula. The natural environment of the Persian Gulf is very rich with good fishing grounds, extensive coral reefs, and abundant pearl oysters, but its ecology has become increasingly under pressure from the heavy industrialisation and in particular the repeated major petroleum spillages associated with recent wars fought in the region.
The Red Sea occupies a part of the Great Rift Valley, and has a surface area of 438,000 km2. It is 2250 km long and, at its widest point, 355 km wide. It has a maximum depth of 2211 m in the central median trench and an average depth of 490 m (1,608 feet ), but there are also extensive shallow shelves, noted for their marine life and corals. The sea is the habitat of over 1,000 invertebrate species and 200 soft and hard corals and is the world's most northern tropical sea.
The Red Sea is a rich and diverse ecosystem. More than 1100 species of fish[33] have been recorded in the Red Sea, and around 10% of these are found nowhere else.[34] This also includes around 75 species of deepwater fish.[33] The rich diversity is in part due to the 2,000 km (1,240 mi) of coral reef extending along its coastline; these fringing reefs are 5000–7000 years old and are largely formed of stony acropora and porites corals. The reefs form platforms and sometimes lagoons along the coast and occasional other features such as cylinders (such as the blue hole at Dahab). These coastal reefs are also visited by pelagic species of red sea fish, including some of the 44 species of shark.
Approximately 40% of the Red Sea is quite shallow (under 100 m/330 ft), and about 25% is under 50 m (164 ft) deep. About 15% of the Red Sea is over 1,000 m (3,300 ft) depth that forms the deep axial trough. Shelf breaks are marked by coral reefs
Continental slope has an irregular profile (series of steps down to ~500 m/1,640 ft)
Southern Ocean
The Southern Ocean is the fourth-largest ocean, covering 20,327,000 square kilometers. It is typically between 4,000 and 5,000 meters deep with only limited areas of shallow water. The Antarctic continental shelf is narrow and unusually deep, its edge lying at up to 800 meters, compared to a global mean of 133 meters.
The Antarctic Circumpolar Current moves perpetually eastward — chasing and joining itself, and at 21,000 kilometers is the world's longest ocean current, transporting 130 million cubic meters per second — 100 times the flow of all the world's rivers. The Antarctic ice pack fluctuates from an average minimum of 2.6 million square kilometers in March to about 18.8 million square kilometers in September.
A 10-metre (32.8 feet) long colossal squid weighing 495 kilograms (1,091 lb) was captured in the Ross Sea on 22 February 2007.
The Ross Sea toothfish fishery
There are two main species of toothfish:
the Patagonian toothfish, Dissostichus eleginoides, which occurs mainly in Subantarctic waters, and the Antarctic toothfish, D. mawsoni, which is found only in Antarctic waters. The Antarctic toothfish is caught from the Polar Convergence (at about 60° S) south to the Antarctic continent, whereas the Patagonian toothfish is mainly caught north of 65° S. The Ross Sea region is unusual because between these latitudes both species are abundant and show considerable overlap in their distribution. Indeed, over 90% of the longlines set in the fishery in this area have both species on the same line. Both species are found down to depths of over 2000 m
The Ross Sea toothfish fishery is the southernmost fishery in the world. The extreme cold and ice conditions can make fishing both difficult and dangerous. During most of the year the Ross Sea itself is covered by ice. However, during January and February, areas of open water (called polynas) allow access to the continental shelf and slope. Longline vessels (predominantly from New Zealand, but also from South Africa, Russia, and Uruguay) have taken advantage of this to develop an exploratory fishery. They start working in the deep south, and as the season progresses they move north to stay ahead of the freezing sea ice, and by May are restricted to the northernmost fishing grounds. CCAMLR agrees on annual precautionary catch limits. Since 1998, the catch has steadily increased from about 40 t to over 1350 t in 2002 (all of these catches are well within the CCAMLR limits). Because it is a high latitude fishery, Antarctic toothfish has formed over 95% of the catch. Up to three New Zealand vessels have been involved in the fishery in any year. However, in the 2003 season up to six New Zealand vessels are fishing in these waters.[36]
An aerial view of Antarctica. Weddell Sea is the 'bay' in the top left corner.
The Weddell Sea land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. Much of the southern part of the sea, up to Elephant Island, is permanent ice, the Filchner-Ronne Ice Shelf. At its widest the sea is around 2,000 km across, in area it is around 2.8 million km2. The ice shelves which used to extend roughly 3,900 square miles (10,000 km2) over the Weddell Sea have completely disappeared by 2002.
Arctic Ocean
The Arctic Ocean is the smallest of the world's five major oceans and the shallowest.[37] Almost completely surrounded by Eurasia and North America, it is largely covered by sea ice throughout the year. Its temperature and salinity vary seasonally as the ice cover melts and freezes;[38] its salinity is the lowest on average of the five major seas, due to low evaporation, heavy freshwater inflow from rivers and streams, and limited connection and outflow to surrounding oceanic waters with higher salinities. In summer the icepack shrinks about fifty percent.[37]
Endangered marine species include walruses and whales. The area has a fragile ecosystem which is slow to change and slow to recover from disruptions or damage. The Arctic Ocean has relatively little plant life except for phytoplankton. Phytoplankton are a crucial part of the ocean and there are massive amounts of them in the Arctic. Nutrients from rivers and the currents of the Atlantic and Pacific oceans provide food for the Arctic phytoplankton.[39]
^Hopley, David; Smithers, Scott G.; Parnell, Kevin E. (2007). The geomorphology of the Great Barrier Reef : development, diversity, and change. Cambridge : Cambridge University Press. p. 27. ISBN978-0-521-85302-6.
^Galil, B.S. and Zenetos, A. (2002). A sea change: exotics in the eastern Mediterranean Sea, in: Leppäkoski, E. et al. (2002). Invasive aquatic species of Europe: distribution, impacts and management. pp. 325-336.
^NZ National Institute of Water & Atmospheric Research (2003) [www.niwa.cri.nz/__data/assets/pdf_file/0007/29842/fau-2003-06.pdf Fisheries & Aquaculture Update.] No 6. Retrieved 2 May 2008.
