Multivariate determination of Atlantic herring population health in a large marine ecosystem

Atlantic herring are among the most harvested marine fish species globally and are of extraordinary ecological and economic importance. Within the Scotian Shelf and Bay of Fundy management zone (NAFO Division 4WX), herring support one of the largest fisheries in Canada, yet the conservation status of the stock is currently unclear. We use field observations, stock assessments, and published studies to evaluate the long-Term (1965-2016) status, or health, of 4WX Atlantic herring based on 33 indicators that serve as proxies for the ecological dynamics across the larval, juvenile, and adult stages. Sixteen indicators that showed evidence of significant and synchronous temporal changes were integrated to produce a standardized series of herring population health. This multivariate index exhibited a gradual, long-Term decline punctuated by a more rapid decline between 1980 and 2005. Following normalization, future trajectories of herring spawning stock biomass (SSB) over this period were best forecast by the average weight of herring (r² = 0.63; lag = 6 years) and indicated that SSB would remain low over the next 6 years. Our study suggests that integrating factors related to population health can provide deeper insight in situations where individual series are uncertain and can complement existing assessment approaches.