Ecosystem services provided by the Baltic Sea ... - Naturvårdsverket

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SWEDISH ENVIRONMENTAL PROTECTION AGENCY Report 5873 • Ecosystem services provided by the Baltic Sea and Skagerrak Economic Marine Information reported when landed. Recently, the European Commission inspected fishing vessels throughout the Baltic and found that vessels consistently reported proportional differences between landing weights, when inspected and when not inspected (150). In the case of Poland the inspected landings were on average 48.7 % higher than the uninspected. According to the investigation, surveys of Swedish vessels indicated the second highest proportion of unreported fishery among the surveyed states (21.4 %). A subsequent investigation by the SBF suggested that this figure was overestimated and the figure was accordingly corrected to 8 %. In Lithuania the difference was 15.6 %, in Germany 13.6 %, in Demark 12.7 % and in Latvia 8 %. The proportion of assumed illegal fishing were then subtracted from the respective country‘s TAC in 2007. Figure 14. European plaice. © Kajsa Garpe The combined threats of over-fishing and eutrophication It should be noted that excessive uptake of one species not only jeopardizes the population of this particular species, but may further cause altered interspecific processes with implications for food web dynamics and ecosystem function and, as a consequence, loss of other ecosystem services. If, for example, the number of predators is reduced, plankton-eating fish may increase. In the Baltic, the decline in cod populations has favoured their prey, sprat. This may, in turn, decrease the number of zooplankton, which feed on phytoplankton. Consequently, the loss of top predators may result in eutrophication and reduced water transparency – a typical case of top-down control. Sprat dominance is believed to be further stabilized by increased predation on cod eggs and larvae by sprat (37) as well as by the competition between sprat and cod juveniles for zooplankton food (151). As an example of bottom-up control, the deterioration of water quality, due to eutrophication has consequences also for top predators, such as cod, thus creating a feedback loop. 97
SWEDISH ENVIRONMENTAL PROTECTION AGENCY Report 5873 • Ecosystem services provided by the Baltic Sea and Skagerrak Economic Marine Information Juvenile cod are often associated with macroalgal beds or sea-grass, habitats which are sensitive to light conditions and may become limited in extent with decreased water transparency. In summary, over-extraction may exacerbate loss of habitat with consequences for recruitment to the adult population. Flatfish, like the European plaice (Pleuronectes platessa; Fig. 14) are also significantly affected by eutrophication. Their recruitment is negatively affected by abundant filamentous algae covering shallow soft bottoms. The recruitment loss resulting from current dominance of algal mats has been estimated to result in a 30 – 40 % reduction in commercial catches (152). Commercial catches of perch, pike (Esox lucius) and zander have also declined significantly in the Baltic proper (Fig. 15). Regarding perch and pike this is believed to be the result of major recruitment problems (153). 100 tonnes 80 60 40 20 0 1994 1995 PERCH PIKE ZANDER 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 Figure 15. Swedish commercial landings of perch, pike and zander in the northern Baltic proper (Kalmarsund – Stockholm). Source: Fiskeriverket 2008 (81). Pollution On the one hand we are recommended to eat fatty fish due to its health-promoting content of omega-3 fatty acids. On the other hand, there are constraint to the recommended intake due to high levels of environmental pollutants, such as dioxins and PCBs. Moreover fatty fish from the Bothnian Bay cannot be exported to other EU countries due to its toxicity. Although concentrations of PCBs have been significantly reduced, they remain high in the Baltic proper (154). Similarly, unsatisfactory levels of dioxins are maintained and have not decreased further since their initial reduction in the 1980s. Today, some of the hazardous substances threatening the provision of food fit for consumption include heavy metals, PFCs (perfluorinated substances), BFRs (brominated flame retardants) and TBT (triorganic tin compounds), the latter released from anti-fouling paint and known to cause sterility and other hormonal disorders in marine invertebrates (155). In addition, cadmium levels in Baltic mussels are high (three times those in Skagerrak) but have at least ceased to increase. Although sub-lethal effects of 98
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