18.104.22.168 Changes in marine fisheries
Northerly geographical range extensions or changes in the geographical distribution of fish populations have recently been documented for European Continental shelf seas and along the European Continental shelf edge (Brander et al., 2003; Beare et al., 2004; Genner et al., 2004; Perry et al., 2005). These geographical movements have been related to regional climate warming and are predominantly associated with the northerly geographical movement of fish species (sardines, anchovies, red mullet and bass) with more southern biogeographical affinities. Northerly range extensions of pelagic fish species have also been reported for the Northern Bering Sea region related to regional climate warming (Grebmeier et al., 2006). New records have also been observed over the last decade for some Mediterranean and north-west African species on the south coast of Portugal (Brander et al., 2003). Cooling and freshening of the North-West Atlantic (e.g., in the sub-polar gyre, Labrador Sea and Labrador Current) over the last decade has had an opposite effect, with some groundfish species moving further south (Rose and O’Driscoll, 2002) in the same way as plankton (see 22.214.171.124).
Regional climate warming in the North Sea has affected cod recruitment via changes at the base of the food web (Beaugrand et al., 2003). Key changes in the planktonic assemblage, significantly correlated with the warming of the North Sea over the last few decades, has resulted in a poor food environment for cod larvae, and hence an eventual decline in overall recruitment success. This is an example of how the dual pressures of over-fishing and regional climate warming have combined to negatively affect a commercially important fishery. Recent work on pelagic phenology in the North Sea has shown that plankton communities, including fish larvae, are very sensitive to regional climate warming, with the response varying between trophic levels and functional groups (Edwards and Richardson, 2004). The ability and speed with which fish and planktonic communities adapt to regional climate warming is not yet known.