The importance of fisheries

The Swedish fishing, aquaculture and production industry employs a total of around 5,000 people and has an annual turnover of around SEK 5 billion. Cod and the pelagic species are responsible for ¾ of the total catch value of Swedish fishing (1).

Changes in the Baltic Sea

The Baltic Sea is a unique inland sea with brackish water and special ecosystems. The conditions are largely governed by factors that have the potential to change if the climate changes. The sea water temperature is affected directly by a rising air temperature. Salinity and oxygen content are affected by the turnover of water, which in turn is controlled by precipitation and wind conditions (1).

The Baltic is considered a threatened sea. The temperature in the Baltic Sea will rise by several degrees and the extent of ice cover will decrease substantially. With increasing westerly winds and a substantial increase in precipitation, the salt level will be almost halved. If this happens, dramatic changes will occur in which almost all marine species will disappear (1).

Even more modest effects on salt levels, together with the rise in temperature and increased input of nutrients, will probably lead to large-scale consequences and an increased burden on an already polluted sea. Modelling calculations indicate that algal blooms will increase in the southern Baltic, while they may decrease elsewhere. There is great uncertainty on how the aggregate changes will affect biology (1).

An increase in temperature of 2.5–4.5°C, which is predicted in the scenarios towards the end of the century, will have various effects on fish communities depending on the depth conditions in the environment in question. The thermocline will be displaced away from the coastline, moving to a deeper level. This means that the warm-water species will have more space in which to live, at the expense of the cold-water species. The extent of the change will depend on the depth conditions in the environment in question (1).

Living space for marine species in the Baltic Sea is expected to decrease due to the reduction in salinity that is predicted in most climate scenarios. The extent of the changes will depend on the extent of the reduction in salinity. The flow situation in freshwater sources entering the Baltic will change, with less seasonal variation but a greater overall outflow, primarily from the rivers in Norrland. …There is great uncertainty regarding the extent of the change. The results from several global climate models vary, showing everything from an average fall in salinity at the sea surface of 45% to a statistically insignificant increase of 4%. The interface between salt water and surface fresh water (the halocline) will remain, but will be around 10 metres deeper than today (1).

It is difficult to calculate the changes in the overall balance, however, and there is currently no overall scientific consensus on the impact of climate change on the total nutrient supply to the Baltic Sea (1).

In a long-term perspective, there is an unequivocal trend towards increasingly low oxygen levels across all major areas. Oxygen deficiency also occurs in large parts of the Kattegat during the late summer and early autumn (1).

Vulnerabilities

In particular, the stocks of cod in the Baltic Sea, the Kattegat and the North Sea are threatened with collapse. The high pressure from fishing has resulted in a reduction in the average size of the fish, and adult fish now constitute a smaller proportion of the total biomass. The reduction in cod can also be linked to changes further down in the chain in the Baltic Sea’s eastern basins, where the amount of zooplankton in the spring and early summer has decreased, which correlates with grazing by the large stock of sprats (1).

There is a great deal to indicate that the reduced importance of cod in the ecosystem has produced consequences at several stages, which has resulted in a regime shift taking place in the Baltic Sea. The majority of the Baltic Sea will be dominated by ecosystems that are more reminiscent of inland lake conditions, and the level of biodiversity will decrease.… Cod fishing currently represents 25% of the total value of Swedish fishing, around SEK 200 million annually.Flatfish will also decrease in the Baltic Sea …. New species will gradually colonise Swedish waters and may seriously disrupt ecosystems (1).

The eutrophication of lakes and watercourses increases. Fish are seriously affected through changes in species composition and a shift towards warm-water species. Foreign species will also spread out further. Overall fish catches may increase, particularly in certain lakes (1).

Cod being wiped out in the Baltic Sea would entail a reduction in catches equivalent to SEK 200 million annually. In total, the fishing industry would suffer losses of around SEK 230 million annually. Calculated on the basis of a successive change through until 2100, this will give rise to reduced earnings of approximately SEK 15 billion. The increased aggregate costs of damage for drinking-water supply and fisheries in Sweden in the period 2010-2100 would be 60-140 SEK billion (1).

The total loss of cod fishing in the Baltic Sea would have a very serious impact on a large proportion of the Swedish fishing industry, as the leading value-creating species in the Baltic would be lost. This would probably also have significant consequences for both employment and the cultural environment in smaller towns and fishing villages, primarily in south-eastern Sweden (1).

In general it is difficult to distinguish the impacts of climate change on fisheries from other anthropogenic impacts when observed by means of conventional ecological criteria regarding the abundance, growth and catches of different species (2).

In the long run, climatic warming may have a significant effect on the state of waters, fish stocks, fishing and fish farming but, in the short run, other factors such as market conditions, fishing restrictions, increase of the grey seal population, reduced fishing capacity and natural variation of fish stocks will have a significantly greater impact than climate change on occupational and leisure fishing (3).

Benefits

A general increase in North Atlantic and Arctic fisheries is likely, based on traditional species as well as the influx of more southerly species. This will affect East Greenland, Iceland, Norway, Sweden, Finland, Northwest Russia, and adjacent seas (4).

An increased yield of marine warm-water species can be anticipated as a result of the inward migration from the south of species such as mullet and European sea bass. Increased bottom water temperatures also entail higher growth for lobsters, crabs and Norway lobster. Catches of Norway lobster have increased by 30% over the past two warm years, for example (1).

Despite the negative consequences for especially cod, total fish production will probably increase in fresh water, as the warm-water species, including commercially important species such as pike, zander and perch, will be able to spread further across the country due to higher temperatures and an increased supply of nutrients to watercourses as a result of increased runoff (1).

Adaptation strategies

The EU has a clear role to play in reducing the input of nutrients to the Baltic Sea. The EU’s marine strategy and the EC directive linked to the strategy to some extent improve the prospects of initiatives in support of the Baltic. A common Baltic Sea Action Plan can make a further contribution to create the necessary basis for extended efforts (1).

In freshwater and in the North Sea, there is a clearer trend towards greater numbers of warm-water species and a greater spread of these northwards. To make it easier for species to spread to new lake systems and thereby to facilitate the preservation of a particular fish, even when cold-water species are declining due to climate change, it is essential for migration opportunities between and within water systems to be maintained or increased. Alternatively, the artificial distribution of fish can be considered (1).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Sweden.

1. Swedish Commission on Climate and Vulnerability (2007)
2. Marttila et al. (2005)
3. Ministry of the Environment of Sweden (2009)
4. ACIA (2004)