Harbor porpoises on the decline in the German North Sea

(Frontiers) The harbor porpoise population is declining in the German North Sea, according to a recent study which surveyed the species over a 20-year time period. Harbor porpoises are known as a "sentinel species" - animals which indicate the health of an ecosystem and point to potential risks (think of the canary in the coal mine) - and their decreasing numbers indicate the extent to which human activities have affected marine wildlife.