Oceanographic Variability Constrains Recovery of Overexploited Cod and Haddock on the Faroe Bank: Evidence for Environmental Recovery Windows at Low Stock Size

ABSTRACT

In a changing global ocean certain fish populations are approaching the upper limits of their thermal tolerance. Understanding how a warming climate and plankton dynamics affect stock recovery is thus a central challenge for fisheries management. Here we use the Faroe Bank ecosystem in the northeast Atlantic as a climate‐sensitive case study to investigate how environmental variability influences recovery of demersal fish stocks following overexploitation. Atlantic cod ( Gadus morhua ) and haddock ( Melanogrammus aeglefinus ) on the Faroe Bank declined rapidly after 2003, collapsed in 2005 and remained in a prolonged low‐abundance state until 2018–2020, despite a commercial fishing moratorium implemented in 2008. Using ~25 years of fisheries, biological and oceanographic observations, we evaluate environmental factors associated with this delayed recovery. Initial stock collapse was driven by heavy exploitation, whereas the prolonged low‐abundance state appears to have been reinforced by depensatory dynamics under relatively warm and less productive ecosystem conditions. Stock recovery began only when spring bottom temperatures declined in 2015–2016, coinciding with increased phytoplankton productivity, improved 0‐group fish growth and the return of sandeel ( Ammodytes spp.). We identify two interacting environmental bottlenecks limiting recovery at low abundance: (i) relatively warm and low‐productivity conditions limiting pelagic 0‐group growth and survival and (ii) temperature‐productivity constraints on 0‐group sandeel abundance reducing the availability of a key lipid‐rich prey resource for recovering stocks. The resurgence of 0‐group sandeel preceded increases in adult cod and haddock biomass and coincided with cooler, more productive conditions associated with variability in the subpolar gyre. These results suggest that the success of management actions to rebuild chronically depleted stocks can depend on “environmental recovery windows”, when reduced fishing pressure coincides with favourable temperature and trophic conditions. The Faroe Bank ecosystem therefore demonstrates how modest climatic variability can strongly influence stock rebuilding, with important implications for ecosystem‐based fisheries management under continued ocean warming.