Effects of contaminants on marine mammals
Effects of persistent organic pollutants (POPs) have been found on the hormone, vitamin, enzyme and immune systems of polar bears. Lower concentrations of pollutants may mean that these effects will decline in the years to come. Since the fitness of polar bears and their food supply can vary considerably in the course of a year, there will be periods when bears will be more prone to the effect of the fat-soluble pollutants.
The sea ice is the most important polar bear hunting ground. The primary threat to the polar bear will therefore be global warming and melting sea ice. If these lead to food becoming less readily available, the concentration of contaminants may rise because the polar bear must turn to its body fat and burn that, but it is not clear how the contaminants will affect the bear in such periods. Changes in the type of prey due to altered habitat use may also result in changes in how the animals are exposed to different types of contaminants. Future studies will be able to reveal how levels and effects of different substances may be determined by changes in habitat use as a consequence of climate change.
The levels of PCBs, DDT,, brominated flame retardants and toxaphene are significantly lower in ringed seals from Svalbard than those from the Baltic Sea. Based on the current level of contaminants in Svalbard ringed seals, there is no reason to believe that contaminants are affecting their immune, hormone or reproductive systems. However, as the ringed seal may experience periods with little food, and since it loses weight when moulting due to eating little, it cannot be ruled out that contaminants can affect the health of ringed seals in Svalbard in these periods.
The principal threat to the ringed seal is, like the polar bear, global warming which melts the sea ice. The ringed seal depends upon the ice to give birth, suckle, rest and moult. It uses ice exclusively when it is not in the sea, and never lies on land. It also uses ice-covered areas to seek food.