Distributional shifts of species in the North Atlantic: the rule or the exception?

This work addresses recent shifts in the distribution of marine pelagic fish in the northern North Atlantic and attempts to set them in the context of climate variability, climate change, population dynamics and migration processes. Shifts in the distribution of North-east Atlantic mackerel, and the associated political dispute over fishing rights, has drawn much attention in recent years. However, a closer examination of spatial distributions of pelagic fish in this region suggests that such shifts are not by any means unique: several other examples, both well- and less-well-known, are presented and discussed here. These examples are then used to illustrate the potential importance of various mechanisms that can control the distribution of these species, such as climate variability and change, and population and migration dynamics. A set of simple analytical approaches is demonstrated that can be used to assess the relative importance of each of these mechanisms. Finally, these observations are drawn together to reveal a picture of a dynamic ecosystem in a constant state of flux and to emphasis the necessity