BALLAST WATER EXCHANGE AREAS. Prospects of designating BWE areas in the Skagerrak and the northern Norwegian Trench

Typ: Rapport
Serie: Oceanografi 88
Författare: Pia Andersson


Investigations were made to find out if there are areas with suitable environments for ballast water exchange (BWE) in the Skagerrak and the Norwegian Trench. Suitable conditions may be areas of certain depths (preferably >200 meters) or distance from the coast (preferably >200 nm or >50 nm). Certain oceanographical, biological and envitonmental issues should also be considered. In the Skagerrak there is no area >50 nm from the coast, but there is a small area within the Swedish territorial waters with depth >200 m. There is an area >50 nm from the coast with depth >200 m in the northern Norwegian Trench. Discharged ballst water in the BWE areas will be transported towards a coast or protected area. The main distance between the potential Skagerrak BWE area and the Natura 2000 areas are 10 to 15 nm. There are strong currents in both BWE areas and discharges could be transported over large areas during the following month. The entire Skagerrak area would be reached. Most parts of the costal zone would be reached within a week. The probability that a BW discharge will reach the nearby Natura 2000 areas is high. The shortest drift time to the protected areas along the Swedish coast and to the Norwegian coast is only a few days. A ship would have to stop or greatly reduce its speed to complete a BWE within the proposed Skagerrak area. In the northern Norwegian Trench, there is no major shipping lane nearby. The wave climate in the Skagerrak may not cause major concern for the safety for large ships. In the northern Norwegian Trench BWE area of interest, wave heights are a significant hazard on board most ships. Nutrient levels are not low enough to efficiently reduce the survival rate of the organisms introduced by BW. Discharged pollutants could normally affect the protected areas if transported to the area. There is no way to say what specific salinity level kill BW organisms since there are many different organisms in the BW. As a rule of thumb, there is always a risk that they may survive. If the organisms are harmful, they can or will affect vulnerable native organisms. The environment at the BWE area or in nearby protected areas, possibly with important assets, can be affected by the BW, although it is dependant on the BW contents. There is a wide variety of what it can contain. If the organisms or pollutants are harmful to a single species or to entire ecosystems, there is a clear risk of affecting protected areas. Important assets like fish and mussel farms can be affected. Competing or predatory species may cause harm, especially in spawning areas of fish or on benthic native species. Circulation of the central Skagerrak surface waters and eddies in the northern Norwegian Coastal Current, increase the risk of ships taking up previously discharged BW. The waters in the BWE areas have strong stratification, which prevents mixing with deep water. The risk of uptake is high, albeit with a reduced concentration. In many of the referenced texts however, the concentrations of the organisms are not of major importance. New organisms may survive and reproduce even at low starting numbers. Most results indicate that the proposed BWE areas are not suitable for BWE with reference to the requirements in the Ballast Water Convention and G14.