Fisheries Research

Since 2020 there is a fishing ban for the cod. However, ALKOR Expedition AL594 is not engaged in commercial fishing, but in research. Trawling has been conducted in the deep basins of the Baltic Sea since 1986. The expedition continues one of the best available multidisciplinary long-term data series for the Baltic Sea.

The scientists from GEOMAR caught and measured about 2,000 cod for their studies, but among them was only one fish over 50 centimeters long. In the 1980s, cod up to one meter long were still regularly caught in the central Baltic Sea.

The researchers believe that years of intensive overfishing is the reason. The large cod were all fished away. What remained were only the small specimens, which passed on their genes to the next generation. In this way, the cod in the central Baltic Sea has been practically bred small over the years.

The ALKOR expedition AL594 was underway for 15 days. Off the coast of Schleswig-Holstein, cod larvae were caught with so-called bongo nets. These larvae drift through the sea. Using current models, the scientists later want to calculate where the corpses are located.

The scientists will need almost a year to process and evaluate all the data from the expedition. These data could be crucial for the planning of the future Baltic Sea National Park with regard to regions that are suitable as habitats for fish stocks worthy of protection. All photos: Sarah Kaehlert/GEOMAR

Fisheries Research

Fish - food and livelihood for the growing world population, industrial sector and a finite resource. Within a few decades, industrial fishing has spread from the classic fishing areas in the northern hemisphere to all seas. Many stocks of edible fish are considered overfished and have collapsed. However, the situation is not hopeless. Various countries have now shown that fish stocks can indeed be rebuilt through sustainable fisheries management. Researchers at GEOMAR are therefore looking at fish as a resource from different perspectives. Their common goal is to find new solutions for environmentally sound fisheries management.

What is overfishing?

Even in the late Middle Ages, sturgeon, rays, porpoises, sea lampreys and lobsters were caught on the North Sea coast. Image: The fish market, Frans Snyders (1618)

Atlantic bluefin tuna (Thunnus thynnus) in the fishery hall Altona near Hamburg 1931 before the auction. The tuna stock in the North Sea and Baltic Sea is already extinct decades ago. Photo: Emil Puls, Source: SHMH-Altonaer Museum, Inv.-Nr. 2-1478a

Overfishing: More fish are caught than regrowth

More fish are caught than regrowth: fishing pressure (F) on a stock is higher than that which can produce maximum sustainable yield (MSY). Illustration: Christoph Kersten/GEOMAR

Fish stocks are too small: spawning biomass (B) is smaller than a certain minimum size that can produce maximum sustainable yield (MSY). Illustration: Christoph Kersten/GEOMAR

According to an analysis of 397 fish stocks in European waters from 2013 to 2015, only 46 stocks (12 percent) meet sustainable fishing criteria. Illustration: Christoph Kersten/GEOMAR, Source: Froese et al. 2018 Marine Policy

Good fish - Which fish can you still eat with a clear conscience?

In Northern Europe alone, about 200 fish stocks are commercially exploited, but only a few of them meet the internationally binding criteria for sustainable fishing. GEOMAR has joined forces with the German consumer organizations and some NGOs to jointly publish an annual list of those marine fish that consumers can still eat with a reasonably good conscience.

Here, researchers from GEOMAR take over the scientific assessment of sustainable stock size and sustainable fishing pressure and verify compliance with these criteria. They are guided by the United Nations Convention on the Law of the Sea and its implementation in the EU's Common Fisheries Policy. According to this, fish stocks must be larger than a certain minimum size that can produce the maximum sustainable yield. In addition, fishing pressure on a stock must not exceed that which can produce maximum sustainable yield in the long term. Additional criteria, such as low-impact and low-bycatch fishing methods, are assessed by the other partners.

The fish and marine animals on the joint "Good Fish" list meet these criteria, in some cases with conditions that determine whether they remain on the list in the future. This is also intended to improve fisheries management. The list explicitly does not claim to be complete.

Baltic plaice (Pleuronectes platessa), fishing area: Baltic Sea, permitted gears: pots or traps — **Baltic plaice**
*(Pleuronectes platessa)*

Fishing area: Baltic Sea

Acceptable gears: pots and traps

Baltic Sea flounder (Platichthys flesus), fishing area: western Baltic Sea, permitted gears: pots or traps — **Baltic Sea flounder**
*(Platichthys flesus)*

Fishing area: Western Baltic Sea

Acceptable gears: pots and traps

Baltic Sea dab (Limanda limanda), fishing area: Baltic Sea, permitted gears: fish traps or traps — **Baltic Sea dab**
*(Limanda limanda)*

Fishing area: Baltic Sea

Acceptable gears: pots and traps

Extract from the list "good fish". Plaice, flounder and dab are flatfish that live mainly on the seabed. The stocks in the Baltic Sea are doing well and are fished sustainably if caught with traps and pots.

Aquaculture is no solution

Conversion of mangrove forest to commercial aquaculture ponds at Krishna river delta, India Photo: Srikanth Mannepuri / Ocean Image Bank

The farming of aquatic life in separated areas, known as aquaculture, is often seen as a supposed solution to the problem of intensive overfishing, but it too cannot satisfy the global hunger for fish and seafood and has already reached its ecological limits. An analysis of the growth rates of aquaculture production shows that the zenith has been passed and the numbers are declining.

Large-scale catching of small inexpensive fish as feed for expensive farmed fish also places a heavy burden on developing countries, African and South American coastal states in particular. Providing most of the world's food fish through aquaculture, with the existing geographic focus, could therefore have serious socioeconomic, nutritional, and food security consequences for the entire world.