Fish is an important food base for humans. The estimated value of fish caught worldwide is about $90 billion per year. This makes fishing an important industry. However, in many parts of the world's oceans, fish stocks are threatened by permanent overfishing. Fisheries and aquaculture worldwide catch about 140 million tonnes of fish and produce fishery products. Until the early 1990s, the development of marine fisheries was characterized by an almost continuous increase in catches. Between the 50s and 1990s, the global land area quadrupled, from less than 20 tonnes per year to about 80 million tonnes. Since the 90s of the 20th century, the total amount of fish, mussels and crayfish caught in the ocean has remained almost constant.
Fish farming is also expanding due to the high demand for fishery products, especially in Asian countries. Aquaculture is one of the fastest growing food industries, with an annual growth rate of about 7%. Today, its share of global fish production exceeds 40%. However, many fish farmed in aquaculture are carnivores and need other fish for food. Therefore, wild-caught fish are used for feeding. Although the amount varies depending on the fish species, on average, about five kilograms of fishmeal and fish oil are consumed for every kilogram of fish produced. In addition, wild-caught fish are used as stockings for breeding. Eating fish raised in aquaculture does not mean that it automatically protects wild fish.
The expansion of marine fisheries has played a large role in the shrinkage of global fish stocks, in part due to the collapse of global fish stocks. Overfishing can affect particularly long-lived species, such as redfish, which only produce offspring in old age. In extreme cases, stocks may even plummet. For example, after years of overfishing, cod stocks in the northwest Atlantic of the United States have plummeted.
North Sea cod stocks have also declined significantly due to intensive fishing. The consequences of predatory exploitation in the ocean can manifest themselves in a typical way (see box on the next page). Experts refer to the self-sustaining population of a species in a geographically limited area. Spawning stocks, i.e. breeding animals of fish populations, are of particular scientific importance. The Food and Agriculture Organization of the United Nations (FAO) does not provide precise definitions for different categories of diseases. For example, the transition between fully exploited and overfished states is not very obvious. According to FAO, managing fish stocks that are close to maximum production and have no room to expand catches are considered fully exploited. Overfished fish are considered to exceed sustainable levels. This can be seen in the fact that inventories continue to decrease. One stock has collapsed and its catch is well below historical observations, even under high fishing efforts. When catches begin to rise again after a crash, the stock is expected to recover.
FAO estimates that the proportion of overfished and collapsed stocks has increased since the 70s of the 20th century. In 2006, the share of underutilized equities fell by half again.