Report of the Working Group on Small Pelagic Fish, their Ecosystems and Climate Impact (WGSPEC)

The Working Group on Small Pelagic Fishes, their Ecosystems and Climate Impact (WGSPEC) has met during its second reporting period (2013–2015) in Malaga (Spain), Santa Cruz de Tenerife (Spain) and Thessaloniki (Greece). Scientists from the General Mediterranean Fisheries Council (GFMC) from Greece, Italy, Spain and Turkey played a vital role in the WG. The meetings were attended by experts in climate variability, physi-cal oceanography, zooplankton and fisheries biology.The overarching theme of the WG was the impact of the Atlantic Multidecadal Oscilla-tion (AMO) and related physical drivers such as the contraction of the subpolar gyre, the weakening of the North Atlantic Oscillation (NAO) and the eastward shift of the Iceland-ic Low on the dynamics of Eastern North and Central Atlantic ecosystems including North Sea and Mediterranean. The early focus of the WG was on small pelagic fishes. Dynamics of abundance and migrations of populations of small pelagic clupeoid fish such as anchovy (Engraulis encrasicolus), sardine (Sardina pilchardus), sardinella (Sardinella aurita), sprat (Sprattus sprattus) and herring (Clupea harengus) in the eastern North and Central Atlantic between Senegal and Norway vary in synchrony with the warm and cool phases of the Atlantic Multidecadal Oscillation (AMO). This is shown by compiling retrospective data on fish catches and anecdotal observations, which in some cases date back to the mid-19th century. It is not primarily the temperature which drives the dy-namics of the small pelagic fish populations. Instead, the AMO seems to be a proxy for complex processes in the coupled atmosphere–ocean system of the North Atlantic. This is manifested in large-scale changes in strength and direction of the current system that move water masses around the North Atlantic and likely involves the North Atlantic Os-cillation (NAO), the Atlantic Meridional Overturning Circulation (AMOC), the Mediter-ranean Overflow Water (MOW) and the subpolar gyre (SPG). The contractions and expansions of the SPG apparently play a key role. This was particularly obvious in the mid-1990s, when the SPG abruptly contracted with the result that warm subtropical wa-ter masses moved to the north and east. Small pelagic fish populations in the eastern North and Central Atlantic, including those in the Mediterranean responded quickly by changing abundances and migrating northwards. It seems that the complex ocean–atmosphere changes in the mid-1990s caused a regime shift in the ecosystems of the east-ern North and Central Atlantic and the small pelagic clupeoid fish populations are the sentinels of this shift. WGSPEC extended these studies to other components of NE Atlan-tic ecosystems, particularly plankton, larger pelagic and demersal fish species with a par-ticular view to the regime shift in the mid-1990s. WGSPEC also started to assemble and analyse different data sets on early life stages of small pelagics, with the aim of investi-gating the effect of environmental change on their recruitment. The future work of WGSPEC will be a global comparison of climate variability impact on small pelagics.