The fishing sector is an important part of the local economy and social-cultural landscape in many coastal communities: It provides work and attracts economical activity (like tourism), it connects people and gives a cultural identity. Unfortunately, fishing is also associated with environmental problems: many fish stocks are under pressure of overfishing or are overfished. Intensively fished marine ecosystems are sometimes heavily disrupted. This not only undermines the character and natural productivity of our seas, but also endangers the food supply.
According to the 2016 data of the Food and Agriculture Organinisation (FAO) of the United Nations, 30% of the fish stocks worldwide is being overfished. Almost 60% is being fished to the maximum and cannot handle any increase in fishing pressure. It is called overfishing when there is more fish caught than the amount that is recruited in a fish population. This happens when the fishing mortality is higher than the natural recruitment minus the natural mortality in a population. The fish stock will than decrease. If there are no correcting measures being taken and the fishing pressure is not adjusted, the fish stock can get into danger. There will not be enough mature (reproducing) fish to keep the stock on level. Under long-time overfishing, the stock can collapse. Sometimes the fishing pressure is low enough to allow the stock to grow, but the stock is in such a bad shape (by overfishing in the past or natural circumstances) that we still call it an ‘overfished stock’. To determine if there is overfishing, the following criteria are assessed:
- Fishing pressure on a stock (the mortality that is caused by a fishery);
- Stock size, the amount of mature fish in the population
Most fishermen not only catch the targeted fish species in their nets or on their hooks, but also several other species. Unselective seabed disturbing catching techniques lead to bycatch of bottom dwelling animals. With longline fishery the bycatch can also include dolphins, sharks, sea turtles, birds and sea mammals. Catch can also be discarded due to economic reasons: this happens with species that have a low market value, like sea stars and common dab. Sometimes the fishermen try to maximize the the market value of their catch by discarding the less valuable (e.g. the small, damaged individuals). This happens mainly when there is little quota left. This is called high-grading and is prohibited in the pelagic fishery. Since 2015 a discard ban is being implemented in the European Union for commercial species (species with quota).
Damage to the seafloor
The main commercial fishing method in north-west Europe uses bottom trawls, like the beam trawl fishery. A beam trawl uses heavy chains that are towed over the seafloor and rakes the seabed. This causes long-lasting changes in the ecosystem and impoverishment of the seafloor.
A trawl is a very effective method to catch fish. In the bottom trawl fishery a net is trawled over the seafloor. In the flatfish fishery these nets are often equipped with heavy ‘tickler chains’, which are stretched horizontally over the net and turn over the top layer of the seabed and drive out the fish out of the seabed. It looks like that this raking can have a positive effect on the productivity of some flatfish species. However, bottom trawls also disrupt and damage the bottom life, including habitat forming organisms like sea grasses, seaweeds, sea anemones and corals. Research has shown that intensive fishing with bottom trawls can lead to a change in the species composition and the habitat in the sea. For example, the species composition in the southern North-Sea has completely changed in some parts due to bottom raking fisheries. It is still a good fishing ground for flatfish, but other species have disappeared. Throughout the world, the impact of fishing has led to the loss of special habitats such as seagrass fields, seaweed forests, shellfish reefs and deep-sea coral reefs. Especially the areas that have a low degree of natural disturbance are vulnerable to bottom raking fisheries. The negative effects on the the seabed and species composition can be mitigated by switching to lighter and less bottom raking catching methods and closing vulnerable habitats to bottom fishery.