Plankton effect on cod recruitment in the North Sea

Abstract

TheAtlantic cod (Gadus morhua L.) has been overexploited in the North Sea since the late 1960s and great concern has been expressed about the decline in cod biomass and recruitment1 Here we show that, in addition to the effects of overfishing1 . , fluctuations in plankton have resulted in long-term changes in cod recruitment in the North Sea (bottom-up control). Survival of larval cod is shown to depend on three key biological param- eters of their prey: the mean size of prey, seasonal timing and abundance. We suggest a mechanism, involving the match/mis- match hypothesis2 , by which variability in temperature affects larval cod survival and conclude that rising temperature since the mid-1980s has modified the plankton ecosystem in a way that reduces the survival of young cod.