Ocean fisheries

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 Black Sea.

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 Gulf of Mexico is an excellent example of a passive margin. The continental shelf is quite wide at most points along the coast, most notably at the Florida and Yucatán Peninsulas. An important commercial activity is fishing; major catches include red snapper, amberjack, tilefish, swordfish, and various grouper, as well as shrimp and crabs. Oysters are also harvested on a large scale from many of the bays and sounds.

The Labrador Sea

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]

Many marine species have been almost wiped out because of the sea's pollution. The Mediterranean monk seal is considered to be among the world's most endangered marine mammals.^[24]

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 Scotia Sea. Habitually stormy and cold, about half of the sea falls above the continental shelf.

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).

The Arabian Sea is a region of the Indian Ocean bounded on the east by India, on the north by Pakistan and Iran, on the west by Arabian Peninsula, on the south, approximately, by a line between Cape Guardafui, the north-east point of Somalia, Socotra and Kanyakumari (Cape Comorin) in India.

The maximum width of the Arabian Sea is approximately 2,400 km (1,490 mi), and its maximum depth is 4,652 metres (15,262 ft),

The Bay of Bengal occupies an area of 2,172,000 km². A number of large rivers – Ganges, Brahmaputra, Ayeyarwady, Godavari, Mahanadi, Krishna and Kaveri – flow into the Bay of Bengal. The islands in the bay are very numerous, including the Andaman, Nicobar and Mergui groups.

The Bay of Bengal is full of biological diversity, diverging amongst coral reefs, estuaries, fish spawning and nursery areas, and mangroves. The Bay of Bengal is one of the World's 64 largest marine ecosystems.

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]

An endangered species, the olive ridley sea turtle can survive because of the nesting grounds made available at the Gahirmatha Marine Wildlife Sanctuary, Gahirmatha Beach, Orissa, India.

Bryde's whale which can be seen in the Bay of Bengal is the 10th heaviest animal of the world, weighing in at 22,000 kg (48,000 lb).

Marlin, barracuda, skipjack tuna (Katsuwonus pelamis), yellowfin tuna, Indo-Pacific hump-backed dolphin (Sousa chinensis), and Bryde's whale (Balaenoptera edeni) are a few of the marine animals. Bay of Bengal hogfish (Bodianus neilli) is a type of wrasse which lives in turbid lagoon reefs or shallow coastal reefs. Schools of dolphins can be seen, whether they are the bottle nose (Tursiops truncatus), pantropical spotted (Stenella attenuata) or the spinner (Stenella longirostris) . Tuna and dolphins are usually residing in the same waters. In shallower and warmer coastal waters the Irrawaddy dolphin (Orcaella brevirostris) can be found.^[28][29]

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 Gulf of Oman is a gulf that connects the Arabian Sea with the Strait of Hormuz which then runs to the Persian Gulf.

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)