The Northeast Atlantic blue whiting (Micromesistius poutassou) stock has undergone striking changes in abundance in the last 15 years. The stock increased dramatically in the late 1990s due to a succession of eight unusually strong year classes and dropped again equally dramatically after 2005 when the recruitment collapsed to former levels. The North Atlantic subpolar gyre has previously been shown to have a strong influence on the behaviour of this stock: synchronous changes in the gyre and recruitment suggest a causal linkage and the possibility of forecasting recruitment. A range of mechanisms are reviewed that may explain these observed changes, with two major candidate hypotheses being identified. One hypothesis suggests that the large mackerel (Scomber scombrus) stock in this region may feed on the pre-recruits of blue whiting, with the spatial overlap between blue whiting and mackerel being regulated by the subpolar gyre. Alternatively, variations in the physical environment may have given rise to changes in the amount, type and availability of food for larvae and juveniles, impacting their growth and survival and therefore recruitment. It was not possible to draw firm conclusions about the validity of either of these hypotheses: nevertheless, forecasting recruitment to this stock may be possible in the future if the underlying mechanisms can be resolved.
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