Degraded recruitment synchrony in Northwest Atlantic cod stocks

摘要

Correlated recruitment between North Atlantic cod stocks, separated by hundreds of kilometers, has consistently been interpreted as indicative that a proportion of pre-recruit mortality is forced by large-scaled abiotic conditions. This large-scale pattern was based on analyses that predated the overexploitation-driven stock abundance declines and collapses of the 1990s. We used a sliding window analysis to examine the temporal trajectories of the e-folding decorrelation scales of synchrony of both bottom temperature and de-trended cod recruitment for the Northwest Atlantic from 1950 to 2006. The characteristic scale of temperature synchrony rose from roughly 400 km to 800 km in the 1990s. Rather than mirror changes in temperature as expected, the scale of cod recruitment synchrony declined in the 1990s from roughly 500 km to 250 km, coincident with the severe declines in abundance. Dispersal between populations, another mechanism that generates synchronous population dynamics, may have been an overlooked contributor to recruitment synchrony documented in earlier analyses. Cod are highly mobile, and it has been suggested that they are structured as metapopulations. Over-exploitation may have interrupted these dispersal patterns and the associated metapopulation structure, thereby reducing synchrony. If so, dispersal from the most productive of the remaining populations may be an avenue for future recovery.