Advection of zooplankton onto the Nordic shelves and effects on forage fish, demersal fish and seabirds

The abundance of zooplankton in the Norwegian Sea is of great importance to the ecosystem in the Norwegian Sea and has gained considerable interest in recent years. The East Icelandic Current (EIC) flows southeast towards the Faroes from an area that contains the highest amounts of zooplankton in the Norwegian Sea. The zooplankton biomass in the Norwegian Sea in May has been monitored annually since 1995 in connection with an internationally coordinated ecosystem survey (ICES/PGNAPES). It is noteworthy that the zooplankton biomass has decreased over time with a relatively strong negative shift around year 2005 and a small increase in the last five years. Not surprisingly, the distribution and diet of Norwegian Spring Spawning Herring in May seems to be closely linked to the zooplankton biomass in the southwestern Norwegian Sea.

In connection with the NHK project ”Ecosystem based management of sand eels, demersal fish and seabirds in boreal ecosystems in the North-east Atlantic” (project number 200004, 2020-2022), that synthesized data on forage fish, demersal fish and seabirds in NE Atlantic, it was noticed that the abundance of zooplankton in the Norwegian Sea is of great importance to the productivity of the shelf ecosystems in Nordic waters (Iceland, Faroes, Norway). This hypothesis is not new, but when comparing the various national data it was clear that many of the available time series support this concept. Zooplankton (and probably also nutrients) in the south-western Norwegian Sea is advected with the East Icelandic Current southwards towards the Faroe Plateau and remnants of this water mass, termed Modified East Atlantic Water (MEIW), is observed north of the Faroes and even along the Norwegian Shelf.

Hence, the goal of the project was to evaluate the hypothesis that oceanographic features, i.e. the subpolar gyre (SPG) and the East Icelandic Current (EIC), cause an advection of nutrients and/or zooplankton onto the Icelandic, Faroe and Norwegian shelves that stimulate the abundance of forage fish, demersal fish recruitment and production of seabirds.