The fish populations of the Baltic Sea are burdened by overfishing, oxygen depletion and high levels of hazardous substances, as well as by natural challenges like cold winter temperatures and varying levels of salinity. Many Baltic fish populations are now thought to be dangerously low.
Limited diversity
Relatively few fish species are found in the brackish waters of the Baltic Sea. The dominant commercial species are cod (Gadus morhua), herring (Clupea harengus) and sprat (Sprattus sprattus). Sprat and herring feed on zooplankton, and are themselves food for cod and salmon (Salmo salar).
The distributions of fish species are largely shaped by salinity levels. Marine species dominate in the Kattegat and in the Baltic Proper, while freshwater species are more common in the north and east, and in coastal waters.
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Read about eel, flatfish and sturgeon in the Baltic.
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Cod
Cod (Gadus morhua) is the most important commercially exploited fish species in the Baltic Sea, but current levels of fishing are unsustainable. Stocks are declining rapidly due to overexploitation and unfavourable environmental conditions for hatching.
Annual cod spawning stock biomass
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Cod need salty water
Cod eggs will only float and survive in fairly saline and oxygen-rich water, so their main spawning areas are in the southwestern waters of the Baltic. This is also why cod are relatively scarce in the Gulf of Bothnia and the Gulf of Finland, except after major influxes of saline and oxygen-rich water from the North Sea, when fish may also spawn further north than usual, in the Gotland Deep. The general decline of cod in the Baltic during the 1980s and 1990s is at least partly due to the lack of any major influx of water from the North Sea. In some areas the only waters saline enough for their eggs now lie at depths where there is too little oxygen.
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Salmon
The wild Baltic salmon (Salmo salar) is recovering after having been in danger of extinction. During a period of just four years (1994 - 1998) the proportion of truly wild salmon among the salmon in the Baltic Sea had declined from 14% to less than 8%. Now, the production of wild Baltic smolt has once more increased to up to 1.3 million in 2001 from 0.3 million in 1995, thanks to joint efforts of HELCOM and the International Baltic Sea Fishery Commission.
Saving the salmon
In 1997, HELCOM and the International Baltic Sea Fishery Commission (IBSFC) launched the Salmon Action Plan 1997-2010 to prevent the extinction of the wild Baltic salmon. Attempts will be made to rebuild stocks to at least 50% of their potential reproductive capacity. As part of the plan the IBSFC has listed rivers with naturally reproducing salmon populations whose stocks should no longer be artificially supplemented after 2005.
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Genetic variation is crucial
Anadromous fish such as the salmon spend most of their lives in the sea, but then migrate into fresh waters to spawn. In genetic terms, each salmon river contains a unique population. But many salmon rivers around the Baltic have been dammed to produce hydroelectricity, or have become polluted. Extensive restocking programmes for Baltic salmon have been operating for many years. Salmon fry are raised in artificial hatcheries and then released to compensate for the loss of these natural spawning areas. This has staved off the extinction of the Baltic salmon, but has also inevitably diminished the overall genetic diversity of the population as wild fish interbreed with hatchery-reared fish, which have a low genetic variability. This can make the entire population more susceptible to diseases like the M74 syndrome.
Links
About Baltic salmon
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Herring
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The ubiquitous herring
Several distinct local stocks live in different waters of the Baltic. Some stocks move between the Baltic and the North Sea, including the fast-growing herring that spawn around Rügen Island off the north German coast. After spawning these fish migrate into the Skagerrak and the North Sea for the summer, before returning to the Sound and German waters for the winter.
Ups and downs
According to the International Council for the Exploration of the Sea (ICES), most Baltic herring (Clupea harengus membras) stocks are in reasonable shape, and some could even be considered as under-utilised. Surpluses have been linked to declining populations of predatory fish like cod and salmon. There have also been reductions in fishing due to a fall in the demand for herring.
But some herring stocks are clearly not faring so well, and have decreased in recent years. Autumn-spawning Baltic herring were abundant during the first half of the 20th Century, but have been scarce since the 1960s. The growth rates and general condition of herring in the Baltic Proper, the Gulf of Finland and the Gulf of Riga have deteriorated since the early 1980s. In the central Baltic herring catches have shrunk noticeably, and stocks are considered to be below safe biological limits.
Annual hering spawning stock biomass
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Sprat
The sprat (Clupea sprattus) distributed through most of the Baltic Sea are generally regarded as a single stock. Sprat spawn in open waters in the Baltic Proper, the Gulf of Riga and the Gulf of Finland between March and August. The Gulf of Bothnia is not saline enough for sprat to spawn in.
Sprat is fished both for human consumption and more widely for processing into fish-meal and oil. The annual catch increased after the early 1990s, peaking at 530,000 tonnes in 1997. Reduced predation by cod and favourable environmental conditions for hatching during the 1990s have contributed to an increase in the Baltic sprat stock, which is considered to be within safe biological limits.
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Eel
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The commercial eel (Anguilla anguilla) catch in the Baltic has been decreasing ever since 1955, the first year for which data is available. Shrinking catches indicate that the stock has decreased, but there are still no reliable estimates of the total stock size, and some catches pass unreported. Eel stocks have indeed decreased throughout the species' distribution in western Europe.
There are indications that the Baltic eel stock has been seriously depleted to a level where recovery is difficult. The International Council for the Exploration of the Sea (ICES) has consequently recommended that fishing for eel should be kept to minimal levels, and that a recovery plan should be implemented.
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Flatfish
The commercially most important flatfish in the Baltic Sea are plaice (Pleuronectes platessa), flounder (Platichthys flesus), turbot (Psetta maxima) and dab (Limanda limanda).
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Plaice are mainly caught in the western Baltic, and the total catch fluctuates considerably, probably due to irregular migration of plaice from the Kattegat. Flounder catches indicate that stocks are only being moderately exploited and are more or less stable. Turbot catches increased from around 100 tonnes in the 1960s to around 1,200 tonnes in the mid 1990s, but then fell back to about 600 tonnes in 1999. Dab catches also dwindled during the late 1990s.
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Sturgeon
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The decline and fall of the sturgeon
An endemic variety of the common sturgeon (Acipenser sturio) was once abundant throughout the southern waters of the Baltic Sea, spawning in several major rivers. But only occasional catches have been reported since 1915, and the Baltic sturgeon may already be extinct in the wild. The reasons for its downfall include dams preventing migration to spawning sites, water pollution and other changes in rivers affecting spawning sites, as well as overfishing for meat and caviar.
Although the Baltic sturgeon is now presumed to have disappeared from Baltic waters, HELCOM has set up a project to re-establish the sturgeon in the Baltic region.
Wild sturgeon are extremely rare in Europe, and the only realistic way to save the species is through the rearing of breeding stock in captivity according to long-term reproduction plans designed to preserve genetic heterogeneity.