Ecological impacts of recent extension of feeding migration of NE-Atlantic mackerel intothe ecosystem around Iceland

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Changes in environmental conditions have caused changes in feeding migration of pelagic fish stocks and such changes have been observed for centuries. Changes in migration can be expected to have impacts on the invaded ecosystem for bad or good through for example predation on native species, competition with native species for limited food resources, and/or being a prey for native species. Since around 2006 Northeast Atlantic mackerel (NEAM) has been extending its summer feeding distribution towards north and west, associated with increased sea temperature. The objective of this paper is to evaluate the ecological meaning and impacts of this extension on the ecosystem around Iceland through (i) exploration of its diet composition in comparison to those of two herring stocks feeding in the same area, (ii) providing estimates of weight gain and total food consumption of NEAM there, and (iii) exploring the inter-annual variation in body condition of the three fish stocks. The results show that calanoidea was in highest mass in NEAMs’ stomachs in most areas while calanoidea and euphausiacea in herring. Fish prey was in higher proportion in NEAM than herring. NEAM in Icelandic waters increased in weight by 42%, 43% and 55%, during the summers in 2009–2011, respectively . Considering its abundance estimates in 2010 and 2011 in Icelandic waters, this corresponds to consumption of around 2.2 million tons each year. This invasion does not have apparent impacts on inter-annual variability in body condition of the herring stocks, while NEAM shows a decreasing trend in condition in the area.