Sharp Declines in Lipid-Rich Prey Appear to Alter the Distribution of Coastal Cod Spawning Groups

Gulf of Maine cod have been collapsed along the northern New England (NE) coastal shelf for approximately twenty years.  This study examined fine scale ecological events associated with the loss of spawning components there during the 1960s.  Four temporally separate studies were analyzed to evaluate the effect sharp reductions in local concentrations of alewives near Muscongus Bay had on a bordering coastal cod group.  The results indicate cod abandoned their spawning grounds near alewife nurseries when sharp declines of YOY alewives and juvenile Atlantic herring occurred, but did not abandon spawning grounds located where Atlantic herring were still abundant. A comparison of these changes, based on the historical population structure of cod in northern New England, suggest that the loss of local spawning activity was related to sequential changes in the metapopulation structure that led to the collapse of a subpopulation. This implies that large, stable concentrations of lipid-rich prey species were important in maintaining coastal spawning groups of cod and by deduction were a prerequisite for re-establishing coastal metapopulation nodes.  The analysis of interspecies relationships at multiple ecological scales suggest that re-establishing alewife spawning migrations can be used to rebuild cod populations along the NE coastal shelf.