Persistent pollutants in a salmon population (Salmo salar) of the southern Baltic Sea

Persistent pollutants in an Atlantic salmon (Salmo salar) population spawning in a river of southern Sweden were investigated. The population was characterized by a high growth rate. Some males reached 20-30 kg after 3 to 4 years in the sea. The fat content of migrating salmon varied by one order of magnitude and was the most significant correlate of pollutant concentrations. No relationships were recorded between fat content and gender, age (weight, length), year at sea, or different measures of condition. The reasons for this may be the varied evolutionary strategies for maximizing reproductive output; male salmon may enter the spawning river as small grilse and spawn opportunely, or migrate at a larger size, when they can hold spawning territories in the river. Females have a greater and more uniform size, and spend more energy on gonadal products. The varying fat content of individual fish may also be attributed to foraging in different areas of the Baltic and thereby to migration distances as well as foraging strategies. When pollutant levels were normalized for fat content, other factors such as age (weight, length) were shown to be important for uptake; older fish had higher levels of pollutants than younger ones.