A rich and varied biodiversity, composed by healthy stocks of marine species, plants and their habitats is crucial for the proper functioning of the Baltic ecosystem. Due to the special conditions of the Baltic, only a handful of the so called “cornerstone” species form the basis of the marine food web. Baltic cod is one of those species for example. Helcom, the Helsinki Commission has published the HELCOM Red list of threatened and declining species of lampreys and fish of the Baltic Sea, where they red-list threatened species with high priority that are important for the ecosystem and that at the same time suffered a biomass decline.
In total, 34 species are red-listed with high priority on the Helcom list, because of severe decline mainly provoked by overfishing. Those high-priority species include thirteen different sharks and rays, as well as some highly commercialized fish species like Baltic cod, salmon and autumn spawning herring.
Furthermore, also marine mammals that were once frequent in the Baltic are threatened today. The Baltic harbour porpoise suffered severe declines and is often caught accidentally and found dying in fishing nets, chiefly gillnets.