Once living and ecologically rich marine ecosystems are nowadays exposed to destructive effects of overfishing. Several fish species are already ecologically extinct, i.e. at the edge of their biologically necessary stock size. However, proper management of some overfished species can lead to a sustainable use of fishery yields.

Overfishing occurs when fish are caught faster than they can produce offspring. A fish stock can only be maintained if there are enough adult fish in the stock to replace the animals that have died naturally or by fishing, with sufficient offspring. According to official estimates, at least 33% of the world’s stocks are overfished. Small-scale fishing is taken barely into account in these calculations, illegal fishing and by-catches not at all.

For many marine researchers, overfishing is one of the most urgent problems in the oceans these days. Overfishing of fish stocks affects the entire ecosystem and makes it more susceptible to pollution and human impacts.

The signs of overfished stocks are manifold. If improved catch techniques and higher “catch per unit effort (CPUE)” and longer journey times for fishermen do not lead to higher catch success for a fish species, these are already serious signs of a shrinking or even overfished stock. Many large fish species can no longer be found in the sea, and the size of the fish caught is constantly decreasing. As a result, too many fish are caught before sexual maturity – a vicious circle.

Overfishing also reduces populations of seabirds and marine mammals, which are deprived of food. For many fishermen, fishing is a livelihood and yet they are often set the goal of exploiting fish populations to the maximum.

The list of overfished species is long and many fish populations in waters of the European Union are close to collapse. The EU’s Common Fisheries Policy (CFP) has set a target of eliminating overfishing in EU waters by 2020. Despite catch limits and quotas, 41% of commercial species in the EU are still considered overfished. The ICES (International Council for the Exploration of the Seas) issues annual recommendations on a scientific basis for the maximum catches of fish stocks in the North-East Atlantic, which are often exceeded when quotas are set in the EU. A recovery of many species is still not possible as economic interests are prioritized. The immediate reduction of catch quotas worldwide is a matter of survival for many fish species. But it is also essential to look beyond the borders of the EU and other industrialised nations, where most fish is consumed per capita: Wealthy countries are responsible for 97% of industrial fishing, poorer countries for 3%, but 78% of these 97% come from national waters of poorer countries.

The fisheries committees are called upon to promote sustainable fisheries management through research and to implement the relevant laws. For species to recover there is an urgent need to plan fisheries-free zones where fish can retreat. In 2016, the European Union agreed on a ban on bottom trawls in deep-sea regions of the Atlantic: They may only be used to a depth of 800 metres. However, all other fishing areas in shallower regions or other parts of the ocean remain unprotected. In the case of marine use, the sea should be treated according to the precautionary principle: as long as little is known about fish stocks and fish biology, it should only be used gently or not at all. This applies in particular to the increasing deep-sea fishing on the submarine mountain tops. More than two-thirds of fish stocks are still inadequately known today. One of many examples of overfishing is tuna.


  1. https://www.wwf.de/themen-projekte/meere-kuesten/fischerei/fischereipolitik-in-europa/
  2. FAO. 2018. The State of World Fisheries and Aquaculture 2018 – Meeting the sustainable development goals. Rome.
  3. J. McCauley, C. Jablonicky, E. H. Allison, C. D. Golden, F. H. Joyce, J. Mayorga, D. Kroodsma (2018) Wealthy countries dominate industrial fishing. Sci. Adv. 4, eaau2161
  4. Esther Gonstalla, Das Ozeanbuch, 128 Seiten, oekom verlag München, 2017

Blogposts on overfishing (german):

Factsheets (german):


By-catch means fish and other marine organisms which are accidentally caught in the course of commercial fishing. The less selective the fishing equipment the greater the proportion of unwanted by-catch.

Around 300,000 whales, dolphins and porpoises die this way every year. This means that more whales are currently killed by by-catch each year than at the peak of whaling in the 20th century. Sea turtles, starfish, sponges and rays are also sorted out of the nets and thrown overboard, as are fish of the wrong sex, size or quality. Most animals do not survive this procedure and are decimated unnoticed. Not only animals living in water, but also seabirds, for example, get caught in the nets – around 100,000 albatrosses unintentionally end up in fishing nets every year.

On average, fishermen worldwide throw one kilogram of by-catch back into the sea for every four kilograms of target fish caught. For some fishing gear, such as shrimp trawls, the ratio is as high as 20 kilograms of by-catch to one kilogram of shrimp. Whether sea turtles or sharks: commercial fishing kills millions of additional animals in this way. According to ecosystem estimates, 38 million tons of marine animals are lost every year, which corresponds to 40% of the world’s fish catch. Apart from the ethical justifiability of treating living creatures like garbage, this wastage destroys the fragile marine ecosystem, threatens the basis of fishing and brings species to the brink of extinction. The disappearance of porpoises, sea turtles, deep sea corals and other species reduces the productivity and stability of the marine ecosystem, which can have dramatic consequences, particularly in the context of climate change.

What are the ways out of this dilemma? Global fishermen should work in their own interest to reduce by-catches. So-called “smart nets” can reduce by-catch through specific hook shapes, exit windows and the use of magnetic or acoustic signals and weights. Although some of these methods are effective, they are not the final solution. Following a comprehensive reform proposal for the Common Fisheries Policy (CFP), the European Parliament imposed a landing obligation for all species used for fishing on 1 January 2015. On the one hand, this should create an incentive for fishermen to minimise their by-catch and, on the other hand, oblige them to use the organisms that have already been killed and caught. According to a report by the German Environmental Aid (DUH), however, the by-catch quantities are not sufficiently documented and controlled, so that a far too high proportion of the by-catch is still discarded. There is still a need for action here: for example, surveillance cameras could be used to set up cost-effective and complete documentation of fishing activities. In the interests of all, fishermen, scientists and politicians should work together to find solutions to the by-catch problem, which should not be underestimated.

Ghost nets

Every year thousands of dolphins, whales, sea turtles and sea lions die in commercial fishing nets or in marine debris. The Food and Agriculture Organization (FAO) estimates that at least 640,000 tons of fishing equipment, such as driftnets and longlines, are lost or left behind worldwide each year. Lost nets and other waste wrap around fins and other limbs, causing drowning, infection or amputation.

Some dolphins, porpoises and whales are particularly vulnerable. Often they feed on the same fish species that fishermen target or they simply live in the regions rich in fish. Only the total protection of marine mammals by developing more gentle fishing methods can help here. Furthermore better methods must be developed against ghost nets, lost illegal nets in the sea. The fishermen should, in their own interests, use internal controls to put a stop to the harsh traders, because only sustainable use can guarantee them a catch.

Shark conservation

The international shark conservation is still the problem child of international ocean politics. An estimated 20-50 million animals or more die in nets and long lines of the currently very unselective fisheries industry. The repercussions for the oceans are dramatic.
Until 2013 we, together with the Shark-Alliance n the EU, have worked towards improving fisheries, especially the call for a “fins attached” policy. At the CITES-species protection conference and other committees some successes have been celebrated. However: The EU remains an important trader for shark meat and fins. And in Germany shark products remain on the market. Forgo this “delicacy” and support further educational work of DEEPWAVE regarding the conservation of sharks.

Text: Onno Groß, 2016

Aktualisierung: Franziska Bils und Antonia Uthoff, 2019


Aquaculture or aquafarming is the aquatic equivalent of agriculture or farming on land. Defined broadly, agriculture includes farming both animals (animal husbandry) and plants (agronomy, horticulture, and forestry in part). Similarly, aquaculture covers the farming of both animals (including crustaceans, finfish, and mollusks) and plants (including seaweeds and freshwater macrophytes). While agriculture is predominantly based on the use of freshwater, aquaculture occurs in both inland (freshwater) and coastal (brackish water, seawater) areas.

© FAO SOFIA 2018

In order to feed the world’s growing human population, attention will need to increasingly focus on from where the protein needs of the world will be supplied. While capture fisheries have now reached a plateau of production, marine aquaculture of fish, shellfish, and algae has been steadily increasing over the past decades and has become a valid option to make up the protein shortfall. However, one of the major constraints for the aquaculture production sector is the availability of and access to space. In many coastal areas, competition with other marine activities is already high, mainly because the bulk of marine aquaculture is located close to the shore. Furthermore, water quality in some coastal areas is often not good enough to allow high-quality production. Besides, there is a need for increased ocean protection and the preservation and/or restoration of marine ecosystem health.

However, aquaculture systems can have significant environmental impacts. Building intensive fish-farming aquaculture sites can destroy natural habitats like mangrove forests and cause severe damage to the coastal environments. If we look at the ecological importance of mangroves, we see that mangroves protect coral reefs from sedimentation, provide vital food sources for many fish species and invertebrates, serve as a shelter for prey, protect shorelines from waves, hurricanes and tsunamis, absorb vast amount of carbon dioxide, reduce the risk of coastal erosion and flooding and finally their roots have the ability to filter organic waste and maintain water quality.
This means, that the damage caused due to mangrove destruction includes carbon release and accelerated climate change, reduction in biodiversity and fish stocks, as well as erosion and flooding of coastal areas.

Furthermore, carnivores species in aquaculture farms need to be fed a large amount of fish. This fish is often wild-caught, which comes with all problems associated to classical fisheries.
Every time wild fish is caught for feeding aquaculture fish, there is often bycatch of nontargeted fish species and other aquatic animals, which are simply discarded. Bycatch can negatively affect species such as dolphins, sea turtles, protected fish, and whales by harming and killing animals, contributing to population declines, and impeding population recovery.

Aquaculture facilities can negatively affect the local coastal fish species. Nonnative fish species, disease and parasite outbreaks and the resulting use of antibiotics or other chemicals escape from the aquaculture sites. Specifically, the survival of wild populations can be reduced through the movement of diseases and parasites from farmed to wild individuals, competition with escaped farmed individuals, and hybridization.

Additionally, during water exchange uneaten fish feeds, leftovers, feces, pathogens, and parasites discharge into the wild. Uneaten fish feeds and feces lead to eutrophication, which is when a body of water becomes overly enriched with minerals and nutrients which induce excessive growth of algae. This process may result in oxygen depletion of the water body.

As the demand for high-quality proteins and a reliable food source is rising, a sustainible solution is needed. If all of the above enviromental issues are taken into account and responsible aquaculture practices are established, we can replace the damaging practice of exploiting our oceans with industrial fishing. In this way, and it has already been technologically proven possible in small scale integrated fish farming experiments, aquaculture could be part of the solution to provide food for everyone without sacrificing our future.


A text by Yonathan Kibreab