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 various contaminants have been demonstrated, to date there are no indications of population effects on fish (156). Alien species Alien species, which commonly arrive with ballast water, could if invasive threaten native populations of commercially important fish as well as create problems for the fishing industry. One example of an unwelcome guest is the spiny water flea. The flea originates from the Black Sea from where it was transported via ballast water. The first official sightings of large populations of spiny water flea where made in the summer of 1992 in Pärnu Bay in the Gulf of Riga from where it is believed that it has spread to other parts of the Baltic Sea. When spiny water fleas reach high densities, they aggregate to form a jelly-like mass that resemble wallpaper glue. Fishermen in the Gulf of Finland have reported that flea aggregations make gill nets useless. In a recent memorandum, SBF presents ways in which marine alien and invasive species may threaten fisheries (157). The Swedish National Food Administration has, among others, issued the following advice concerning the consumption of food fish: Fish is healthy food rich in vitamins and minerals Fatty fish like herring, sprat, salmon (Salmo salar) and mackerel (Scomber scombrus) contain polyunsaturated fatty acid which can reduce the risk of cardio-vascular disorders. From a health perspective people should eat more fish. Certain freshwater fishes and fatty Baltic fishes contain exceeded concentrations of environmental contaminants. Therefore pregnant and nursing should be careful. Most consumers do however not need to limit their fish consumption. Limited sustainability of aquaculture The farming of fish-eating fish has many critics. Today farmed fish are typically reared on fish meal and fish oil, originating from wild-caught fish. This production of food for fish from fish is a questionable use of resources (chapter P2). An investigation from the Swedish Institute for Food and Biotechnology (SIK) estimated that if half of the salmon fodder is of marine origin, it typically takes 3 kg of wild-caught herring, sprat or tobis to produce the 1.3 kg of fodder which is necessary to farm 1 kg of salmon, which in turn provides a filet weighing 600 g. In other words, 5 kg of wild caught fish supplies one 1 kg of salmon filet. (158). Another common objection against fish farming is the narrow genetic make-up of farmed animals, as well as the many diseases and parasites that farmed fish may spread, jeopardizes the sustainability of the whole industry. Fish farms further contribute to nutrient release from discarded food and fish excrements. This nutrient input may affect food web dynamics and primary production. Critics argue that while nutrient leakage is battled in other industries, it appears contraproductive to allow for the establishment of major fish-farms, known to release substantial amounts of nutrients to surrounding waters. However, it may be argued that in the Baltic Sea, not all regions are eutrophied and in contrast to nutrient 99
SWEDISH ENVIRONMENTAL PROTECTION AGENCY Report 5873 • Ecosystem services provided by the Baltic Sea and Skagerrak Economic Marine Information leakage from land use, part of the nutrients from fish farms (discarded food) may become ingested by wild fish, thus rapidly reaching higher trophic levels. SEPA is currently financing an investigation of the effects of local nutrient release from fish farms on bottom substrate composition. Although relatively minor and more localized, the farming of mussels also results in increased sedimentation of organic material below farms. Climate change There is concern that fishing and climate change act in concert to reduce exploited population below a population size from which they cannot easily recover (159). For example, effects of diseases and pathogens may become more severe given warmer waters (160). Also, different responses to climate change could affect relationships in the food web (chapter S3), with potential consequences for fishery production. Potential impacts from fish farms Sea lice - migrating fish risk acquiring the infective larval sea lice parasite as they pass through the areas around the cages. Contamination - transfer of infectious disease from farm fish. Genetic dilution - the impact on natural genetic diversity resulting from escaped farm fish breeding with wild naturals. Pheromone barrier - it is theorized that a chemical messenger can be released by caged fish which creates a “fear” marker that will frighten migrating fish from returning to their breeding streams or rivers. Chemical and medicine controls - agents used to control or reduce disease or infestation can have a harmful effect on a significant range of living organisms. There is a European Directive that the fish farm must obey and the Swedish environment agency must enforce. This directive, “The Dangerous Substances Directive” stipulates the limits of concentration of chemicals (specifically medicines) that are used by fish farms. This directive was not made without good reason. Release of nutrients - a fish farm exports nutrients from discarded food and fish excrements. This nutrient input may affect food web dynamics and primary production. Impact to sea floor - the sea floor can be changed in numerous ways by the presence of fish farms. Marine acidification The most recently acknowledged threat, ocean acidification, is potentially threatening a number of resources, including most organisms with calcareous skeletons. This includes shellfish, corals and plankton and may lead to additional distortion of food webs. Moreover, reproductive failure among invertebrates and a possible failure to produce functional ear bones among juvenile fish may cause 100
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Ecosystem services provided by the Baltic Sea ... - Naturvårdsverket

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