‘What happens if we Overfish the Oceans?’
‘What happens if we Overfish the Oceans?’ by Angela Royston
1. Fish feed mostly on other fish in a food chain that relies on phytoplankton — — microscopic plants that float on the surface of the water. For this reason, fish mainly keep to the sunlit waters near the surface. Below a depth of about 200m, the water is dark. Only a few fish can survive here and many of them come up to the upper layer to feed.
2. Many types of fish like cold water. Some of the most plentiful fishing grounds are in cold waters off the coasts of Alaska, Canada and Iceland. In warmer tropical seas, most fish are found around coral reefs. Now many fishing grounds are running out of fish.
3. Large freezer trawlers are the main cause of overfishing. They use computers and sonar equipment to detect and follow shoals of fish. Then they scoop up the whole shoal. Their huge nets are dragged along the seabed or through the water to catch vast quantities of fish. The fish are then processed and frozen on board. In just two days, a freezer trawler can catch as much fish as traditional fishing fleets do in a year.
4. Freezer trawlers damage more than one or two species of fish. As they haul in their catch, they accidentally net or hook many other sea animals, both large and small. In addition, they damage food chains and entire ocean habitats.
Sea animals that are scooped up by mistake along with a shoal of fish are called by-catch. By-catch includes large fish such as yellowfin tuna and sharks. As fish becomes scarcer, trawlers use nets with a smaller mesh, so that young fish and small fish are also caught. For every tonne of wild prawns caught each year, 3 tonnes of other fish are lost as by-catch.
5. Fishing trawlers are one of the reasons why all types of marine turtle are now in danger of becoming extinct. Although it is forbidden to hunt marine turtles in many areas, turtles are still accidentally caught in the nets of fishing trawlers. Turtles are reptiles, which means thy have to come to the surface to breathe in air. The nets stop them doing that and they drown.
6. The number of sardines in the oceans is increasing. This is because the fish that prey on them, such as cod, are decreasing. Scientists are encouraging people to eat more sardines to restore the balance.
7. Fish farms produce large amounts of sewage and other waste, such as uneaten food and dead fish. For example, a salmon farm with 200000 fish produces as much sewage as a town of 62000 people. The pollution is washed into the surrounding water.
8. Farmed fish live so closely together that disease spreads quickly from one fish to another. Diseases caused by bacteria and parasites, such as lice, move from the pens into the water, infecting wild fish. Fish that escape from the pens also help to spread the disease.
9. The fishing industry can protect fish stocks by abandoning large factory ships and using smaller boats. It can stop using hugh nets with a small mesh. Increasing the size of the mesh allows young fish to escape. To catch large fish, long lines with hooks instead of nets can be used. This reduces the amount of accidental by-catch.
10. Overfishing is not the only problem that needs to be solved to protect fish and other sealife. Although pollution from factories, pesticides and oil spills poison the seas, global warming is the biggest danger. The sea is becoming warmer and more acidic, and this is damaging coral reefs and other sealife. Warmer seas allow some fish to move into new areas where they compete with native fish and disturb existing food chains.
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