Oceans and fisheries

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Oceans and fisheries by Mind Map: Oceans and fisheries

1. World fisheries

1.1. As mentioned, over 90 million tonnes of fish (in the widest sense of the word) are harvested every year Fish are always important as a source of protein for people, but are especialy important in some countries of the world such as Japan In order to understand where large numbers of fish can be found you need to study ocean currents and the food webs of the sea.

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1.3. Major ocean currents

1.3.1. Currents, or strictly speaking surface currents, are caused mainly by wind At any particular place in the world the nature of the prevailing wind can be described. This refers to the direction in which the wind most commonly blows at that place. Surface currents are ultimately caused by these winds However, the final direction depends very much on the shape of the land around the ocean at any particular point.


1.4.1. Surface currents: movement of the surface water of the sea in a constant direction Prevailing wind: the direction from which the wind nearly always blows in a particular area.

2. Resources of the oceans

2.1. Food

2.1.1. By far the most important resource that humans obtain from the oceans is fish. The main fisheries are located on the continental shelves this is because the water is shallow there, In addition, nutrients from the land are abundant on the shelf. All these features make the continental shelf a good place for the growth of plants and therefore the fish that depend on them. .

2.2. Wave and tidal energy

2.2.1. There is an enormous amount of energy in the waves that break on the shores all around the world. Wave enregy Wave energy is a form of renewable energy that can be harnessed from the motion of the waves. There are several methods of harnessing wave energy that involve placing electricity generators on the surface of the ocean. Tidal Energy Tidal energy is power produced by the surge of ocean waters during the rise and fall of tides. Tidal energy is a renewable source of energy

2.3. Chemicals and building materials

2.3.1. As oceans cover 71% of the world's surface and 3.5% of seawater is made up of dissolved substances. There are more than 60 chemical elements are dissolved in seawater. Many materials in the oceans have been eroded from the land, where rain and wind break down rocks. These particles and dissolved substances are carried into the oceans via rivers. Some of these substances can be extracted directly, including: Salt Magnesium Gold Tin Titanium Diamonds

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2.3.3. Sand, gravel, and crushed rock are mined for the construction industry, including housing and road construction; however, care must be taken with their disposal, as it can cause physical damage to the seabed and associated habitats. In addition, clouds of fine particles are produced that are later relocated, which interfere with photosynthesis and act as a source of heavy metals that can enter food chains.

2.4. Transport

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2.4.2. Ships have always been an important way of transporting people and goods. Today, shipping is less important for moving people because of the advent of aviation. However, pleasure cruises are still an important economic sector and bulk freight is still best transported from country to country on ships. There are currently over 50 000 merchant (goods-carrying) ships registered around the world.

2.5. Potential for safe drinking water

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2.5.2. With the world's population now in excess of 7 billion, many essential commodities could become harder to obtain. Possibly the most essential of these is safe drinking water. Only a very small proportion of the water on Earth is safe to drink. Water that is salty is not safe to drink because your body has to remove the salt, which would require more water. It is possible to derive safe drinking water from salt water by desalination.

3. The oceans supply food and chemicals, including building materials, as well as providing an important route for the transport of goods, especially bulky goods, around the world. The incessant motion of the sea, in the form of waves generated by the wind and tides caused by the Moon and the Sun, provide a largely untapped source of energy. The edge of the sea has always been attractive to humans and this, and increasingly the open ocean, is a source of tourist opportunities. Finally, in a world always thirsty for clean drinking water, the vast reservoirs of the oceans are increasingly being used for this purpose.

4. Finding the fish

4.1. Fish are animals and so cannot make their own food. Herbivorous fish rely on the primary producers of the sea, which are nearly always green algae called phytoplankton. Carnivorous fish eat the herbivorous ones or other carnivores. They are part of a food web, starting with phytoplankton. So, fish are found where conditions are good for phytoplankton.

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4.2.1. Key terms Phytoplankton: small organisms in the sea that can make their own food and upon which almost all other sea creatures depend for their food Limiting factor: of all the factors that might affect a process, the one that is in shortest supply Euphotic zone: the top 200 m or so of seawater through which light can penetrate and in which photosynthesis can happen

4.3. Phytoplankton make their own food by photosynthesis. my process requires light, water and carbon dioxide. Water is obviously available everywhere in the oceans dnd carbon dioxide easily dissolves in water from the atmosphere. Light is therefore likely to be the limiting Tactor for photosynthesis. Water absorbs light energy end most ocean water has absorbed all of the sunlight by a depth of only 200 m. This 200 m deep zone is called the euphotic zone. Below this photosynthesis will not happen. This is one reason why fish are found where the water is shallower. Shallow water is found over the continental shelves, which are usually no more than 150 m below sea level. Major fisheries are also found on these continental shelves.

5. Exloitation of the oceans: impact on fisheries

5.1. f

5.1.1. The target species is not the only casualty of over-fishing. Wherever fish are caught commercially, the wrong species, the wrong sex or individuals that are too small are also caught. These non-target individuals are referred to as bycatch Shrimp fisheries are known to have the biggest bycatch of all. Worldwide, it is estimated that for every shrimp caught nearly six other fish are also caught. Shrimp fisheries account for only 2% of the world fishery catch but more than 30% of the world's bycatch.


5.2.1. Bycatch: animals caught by fishers that are not the intended target of their fishing effort.