Part of the Northeast Atlantic mackerel population migrates towards the southern spawning area (Cantábrian Sea) at the end of winter. In this seasonal handline fishery targeting mackerel, the most important in the study area that targets this species, the timing of the peak of catches has shifted forward (later) in recent years. This paper presents results pointing to the likelihood that this shift is due to a change in the timing of the spawning migration to the southern area of the Northeast Atlantic mackerel population. Three types of fleet have been identified within this fishery, and in all of them there is a forward shift in time in effort exerted. Moreover, a new model has been defined for the standardization of catch per unit effort (CPUE). The fishing season appears to have shifted forward by 29 days between 2000 and 2006. Nevertheless, changes have been detected neither in the exploitation pattern nor in the duration of the fishing season during the period studied. A shift on this scale has important consequences for the management of the resource, the fleets that exploit it and the resource assessment survey designs that will have to be adapted to this new scenario.

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