The otter (Lutra lutra) in Sweden--population trends in relation to sigma DDT and total PCB concentrations during 1968-99

Polychlorinated biphenyl (PCB) has been suggested as the major cause of the European otter (Lutra lutra) population decline. This study investigates temporal and geographical changes in otter numbers as well as total PCB and sigma DDT concentrations in otters and their food in different parts of Sweden with various pollution impacts during three decades. In Sweden, rare species belong to the State and carcasses of such specimens are sent to the authorities. Two-hundred and eight specimens have been used to investigate temporal and spatial variation in the otter populations during 1968 and 1999. One-hundred and twenty-five of them have been chemically analysed. The population trends in northern Sweden coincide with the temporal trends of the contaminants. When concentrations of PCBs decrease in the environment, otter population increases. Neither aldrin/dieldrin nor mercury pollution seem to explain why the Swedish otter populations decreased dramatically during the 1960s-1980s. In southern Sweden total PCB concentrations are still high and the indications of improvement of the population are weak.