Two components of Northeast Atlantic herring within the same school during spawning: support for the existence of a metapopulation?

• Published in: ICES Journal of Marine Science
• Main Authors: Johannessen, Arne, Nøttestad, Leif, Fernö, Anders, Langård, Lise, Skaret, Georg
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2009
• Subjects: Northeast Atlantic
• Online Access: http://dx.doi.org/10.1093/icesjms/fsp183; http://academic.oup.com/icesjms/article-pdf/66/8/1740/29134868/fsp183.pdf

Abstract Johannessen, A., Nøttestad, L., Fernö, A., Langård, L., and Skaret, G. 2009. Two components of Northeast Atlantic herring within the same school during spawning: support for the existence of a metapopulation? – ICES Journal of Marine Science, 66: 1740–1748. It has been hypothesized that some stocks of Atlantic herring are subject to genetic exchange and therefore should fit the definition of a metapopulation with subunits. Genetic exchange requires spatial overlap of individuals from different populations during spawning. We investigated a local herring population that is assumed to feed and spawn within the semi-enclosed marine ecosystem of Lindåspollene in west Norway, which is connected with the outer fjord only by a narrow sill. Acoustic recordings and gillnet samples demonstrated the mixed presence of two components within a single school throughout the spawning period 2005–2007. Members of the two components were of about the same size and in a similar stage of gonad development at all times, but the age composition was completely different. These observations represent the first documented case of different components being present in a spawning school and provide strong indications of regular interbreeding. Our data suggest that the two components represent autochthonous Lindås herring and allochthonous herring of coastal/oceanic origin, thereby supporting the metapopulation concept. Two alternative explanations, based on one migratory and one resident component of a single Lindås stock, are also discussed.