The relationship between Gulf Stream position and copepod abundance derived from the Continuous Plankton Recorder Survey: separating biological signal from sampling noise

The mean annual abundance of copepods was calculated from ContinuousPlankton Recorder records for the period 1966-1992, and foran area to the north of the UK bounded by latitudes 58-64Nand longitudes 3E and 21W. Spatial heterogeneity of copepodabundance, when combined with changing tow routes, introducedconsiderable noise as well as an artifactual increasing trendin copepod abundunce into the time series. We therefore defineda more homogeneous subarea spanning {small tilde}270 km eitherside of the shelf edge between latitudes 59 and 6IN, withinwhich the noise introduced by changing tow routes was considerablyless. There was a significant (P < 0.01) positive linearrelationship between the annual copepod abundance for this smallhomogeneous subarea and the annual Gulf Stream position betweenlongitudes 79 and 65W. The copepod abundances for the last4 years of the time series (1989-1992) were, however, significantly(P < 0.01) lower than those predicted from the Gulf Streamposition in these years. Evidence suggests that the anomalyof these years was not an artifact caused by poor sampling orchanging tow speeds.