Harbour porpoise (Phocoena phocoena)
Harbour porpoise have seasonally variable, high overall metabolic rates. Maintaining the body temperature of a warm-blooded mammal in cold water uses a lot of energy, as does hunting fast-moving individual fish as prey. Mothers may often be nursing young and pregnant at the same time and so need ample nutrition on a continuous basis. Harbour porpoise therefore need a rich and continuously available supply of food.
Zu den wichtigsten Beutearten in Nord- und Ostsee gehören Plattfische (z.B. Flundern und Seezungen), Grundeln, Dorsche (Kabeljau) und Sandaale.
Harbour porpoise in the North Sea and Baltic Sea mostly prey on flatfish (flounders, sole, etc), gobies, cod and sandeels.
This makes conserving these fish and their habitats critical to the long-term survival of this cetacean species in German marine waters. Harbour porpoise have a highly developed echo-location system. They produce a series of very brief high-pitched clicks and use the echo from these clicks for guidance, navigation and foraging. This near-constant use of biosonar gives scientists a way of detecting the cetacean species acoustically.
Common seal (Phoca vitulina vitulina)
The North Sea common seal population bounced back after a devastating epidemic of phocine distemper virus (PDV) in the 1990s. But the species can easily come under pressure again, as another outbreak showed in 2002. Seal conservation must not be neglected.
Preliminary research findings show that common seals migrate a long way between their resting sites and feeding grounds. In some cases they can even be out foraging at sea for several days without a break. It is thought that they may navigate by salinity fronts, where plankton and hence fish are in ample supply. Common seals are opportunistic feeders and live on a range of different fish species.
Grey seal (Halichoerus grypus)
Grey seals are much bigger than common seals and have a characteristic flat head, conical teeth and a characteristic coloration. Unlike common seals, grey seals whelp in winter. Animals tagged in Great Britain have frequently been sighted on the German North Sea coast off Amrum and Heligoland. Open sea migration routes and gathering places nonetheless remain largely unknown. Regarding the situation of Baltic Sea grey seals, only about 250 individuals remain south of a line from Gotland to the Gulf of Riga, most of them on the Swedish coast. They are very rare on the German Baltic Sea coast. The continued presence of these animals critically depends on the conservation of open sea habitats providing fish on which grey seals can feed, and most importantly of their resting and whelping sites.