NA - Recruitment dynamics of the herring stocks in the western North Pacific and Norwegian Sea

Atlantic herring (Clupea harengus) and Pacific herring (Clupea pallasi) are closely related but biologically distinct species, residing mainly in the Northern parts of the two oceans. Both species are pelagic plankton-feeders and contain both migratory as well as quite stationary stocks. Many stocks in both species are characterized by huge variation in the strength of the year-classes. This proposal aims at integrating, in a comparative manner, the analysis of Norwegian Spring-spawning herring and Hokkai do herring. Herring has large economic importance for the fisheries and are also ecological keystone species. These herring stocks are strongly affected by both internal and external controls. An understanding of their joint effect on demographic parame ters (e.g., survival, growth) is central to predicting changes in population abundance in the face of underlying environmental variability. It is unknown whether the primary factors that affect herring recruitment in the Norwegian Sea and western North Pa cific change over contrasting environmental and climate phases. It is also unknown whether the stage of recruitment control in the herring changes in relation to external variables. This lack of knowledge is particularly severe because it does not provide managers with the understanding of how contrasting environmental and climate phases affect the earliest available index of herring year-class strength. The overarching objective of this research project is to examine the joint effects of density-indepen dent and density-dependent variables on demographic parameters of the herring stocks in the Norwegian Sea and the western North Pacific. To our knowledge, this is the first study that specifically addresses the mediating effects of environmental variabil ity on the intensity of density-dependent forcing and on the stage of recruitment control, and further, compare the effects over different herring stocks in different oceans.