Hajfiske : påverkan på hajpopulationer, ekosystem och människa

Abstract: Sharks are currently spread throughout the world and represent about 1,5 % of the amount of the world's fish species. They belong to the class cartilaginous fish, which means they have a skeleton composed of cartilage, compared to the majority of other fish having a skeleton composed of bone. Different types of shark species have been living in the oceans for over 400 million years. It is not until the mid-1900s that there has been a significant drop of many shark species and todays populations are reducing drastically. Most shark species are currently classified as endangered at different levels and in year 2015 about one-quarter of all cartilaginous fishes were on the IUCN Red List. The reasons that these species have decreased so much is based mainly by the high fishing pressure. This does not mean targeted shark fishery is always the issue, rather the contrary. A lot of research has shown that a major reason that the shark has depreciated in stocks is because they often end up as by-catch of other fisheries. Direct fishery on sharks is based on the market, which today is primarily in large parts of Asia, partly as a delicacy in shark fin soups, but also a large part that goes to various pharmaceutical products. The pharmaceutical products that are created are said to cure or alleviate a variety of diseases, one of them reputed to be cancer. This is based on the claim that sharks do not get cancer and that people are able to cure their cancer or prevent the disease by eating preparations made from shark cartilage. Such a reduction in shark stocks may result in declines that will take, if ever, several decades before they recover. Without sharks on Earth a wide range of processes and organisms would be affected. As many of the shark species are top predators, they are an important foundation of the food chain in the water. By hunting they control several different species, such as sea birds, marine mammals and small fish, which in turn controls other species. Fish regulate a large amount of plankton, which accounts for about half of the creation of oxygen on Earth. Oxygen is something that is essential for the majority of all living things on Earth, particularly humans. For that reason, the shark is seen as a very important keystone in the circle of life, of which the conservation work should be obvious.