Publication Abstract

Cod

Climate change and cod

G.H. Engelhard*, M.R. Heath and J.K. Pinnegar*

Cod’s response to climate change—arguably the most extensively studied among fishes—remains enigmatic, but crucially important given the species’ huge commercial importance. Landings almost throughout the species’ range have recently shown marked, and sometimes catastrophic, declines, at a time when temperatures have generally warmed. Within the North Sea, a northward shift in the mean latitudinal distribution of cod has occurred but there is much controversy as to the causes—whether active migrations (now considered unlikely), higher fishing mortality in the south, local differences in recruitment, or a mixture of this and other causes. Experiments have shown that eggs and larvae develop best at specific temperatures, but also dependent on other factors such as prey. Recruitment is negatively related to temperature in more southerly populations, but positively in the northern ones, with no significant relationships recorded for some stocks at intermediate latitudes. Recruitment has, within the North and Barents Seas, also been shown to be linked to copepod zooplankton (in turn affected by climate), whereas in the Baltic there are links with salinity. Marked maturity changes have taken place in several cod stocks in recent decades; these have been attributed partly to climate, partly to selective effects of fishing, and partly to density-dependent effects through stock depletion. A warmer climate may have had a subtle, positive effect on growth rates. One forecasting study has modelled the possible responses of different cod populations to future climate change scenarios as projected by the IPCC. For Baltic and North Sea cod, several authors have studied implications of projected climate change for future fishery management: where an important point of agreement was that by and large, fishing mortality needs to be reduced at short–medium term, with climate change potentially kicking in on the longer term.

G.H. Engelhard*, M.R. Heath and J.K. Pinnegar*

In: Rijnsdorp AD, Peck MA, Engelhard GH, Möllmann C, Pinnegar JK (eds) Resolving climate impacts on fish stocks. ICES Coop. Res. Rep. No. 301, pp 162-174.