Ontogenetic spatial constraints of sub-arctic marine fish species

Climate change influences ecological processes and biogeochemical cycles of marine environments. Species may respond and adapt to these changes through shifting spatial distributions, but options may be limited by the required occupancy of essential habitats which are anchored in space. Marine fish species typically have complex life cycles composed of multiple life stages with different degrees of habitat preferences. Limited knowledge of when spatial constraints are most likely to occur in marine fish life cycles has impeded the development of realistic distribution forecasts. In this study, we develop and implement analytical techniques to identify spatial constraints, defined by both the consistency through which a particular geographic area is used year after year, and by the extent of such area with respect to the entire population range. This approach is applied to ten case studies including six groundfish species from the Eastern Bering Sea, three from the Scotian Shelf, and one from the Barents Sea. Our analyses illustrate that the early phase of the species’ life cycle is more spatially constrained than older life stages, and that adult stages are more closely associated with particular temperatures or climate velocities. We detected significant species-specific variability in both the degree to which species are anchored in space throughout their life cycle, and the ontogenetic changes of the geographic association. Some of this variability can be explained by the species life history strategy and this provides promising avenues to extend similar analyses to data poor species. The presence of life history spatial constraints, particularly during early life stages, indicates restrictions exist to changes of spatial distribution and thus questions the assertion that global warming will uniformly result in an increase of harvest at higher latitudes and decreases at lower latitudes. Species distribution models are often parameterized from data based on life stages that are highly variable in space, such as the adult stages during summer months which may result in unrealistic forecasts of distribution. Our study develops ecological and analytical insights that are critical for developing accurate projections of species distributions under different climate change scenarios.