Impact of dredged substrate dumping on commercial fish and Lithuanian fishery in the Baltic

Dumping zone in Lithuanian EEZ exists since 1987 and is located at 38–47 m depths 12 miles southwards from Klaipeda sea port. Annual load on the dumping site is around 1.5 mln m 3 of substrate. Fishery investigations proved that the dumping site in fact attracts commercially valuable fish species, especially cod. Abundance of commercially valuable fish species within the dumping site follows overall fluctuations of resources within the whole Baltic area, and corresponds with seasonal cycles of migration as well as circadian rhythms. Biomass of live fish has been calculated both withing and outside the dumping site. In 2003–2005 juveniles and mature adults of twaite shad (Alosa fallax), that exhibit high sensitivity to pollution, were observed in this area. Lon- term multi year observations of cod and flounder caught in the dumping area do not show any increase of incidence of skin anomalies. The region where the dumping site is located was known as one of the most productive areas for trawl fishery before 1987. We estimated an approximate harm to fishing business caused by under-exploitation of resources within the dumping area.