Data for: Coherent long-term body-size responses across all Northwest Atlantic herring populations to warming and environmental change despite contrasting harvest and ecological factors

Body size is a key component of individual fitness and an important factor
in the structure and functioning of populations and ecosystems.
Disentangling the effects of environmental change, harvest, and intra- and
inter-specific trophic effects on body size remains challenging for
populations in the wild. Herring in the Northwest Atlantic provide a
strong basis for evaluating hypotheses related to these drivers given that
they have experienced significant warming and harvest over the past
century, while also having been exposed to a wide range of other selective
constraints across their range. Using data on mean length-at-age 4 for the
sixteen principal populations over a period of 53 cohorts (1962-2014), we
fitted a series of empirical models for temporal and between-population
variation in the response to changes in sea surface temperature. We find
evidence for a unified cross-population response in the form of a
parabolic function according to which populations in naturally warmer
environments have responded more negatively to increasing temperature
compared with those in colder locations. Temporal variation in residuals
from this function was highly coherent among populations, further
suggesting a common response to a large-scale environmental driver. The
synchrony observed in this study system, despite strong differences in
harvest and ecological histories among populations and over time, clearly
indicates a dominant role of environmental change on size-at-age in wild
populations, in contrast to commonly reported effects of fishing. This
finding has important implications for the management of fisheries as it
indicates that a key trait associated with population productivity may be
under considerably less short-term management control than currently
assumed. Our study, overall, illustrates the need for a comparative
approach within species for inferences concerning the many possible
effects on body size of natural and anthropogenic drivers in the wild.