Year class strengths of zooplankton in the North Sea and then-relation to cod and herring abundance

• Published in: Journal of Plankton Research
• Main Author: Rothschild, B.J.
• Format: Text
• Language: English
• Published: Oxford University Press 1998
• Subjects: ORIGINAL ARTICLES; Buchan; North Atlantic
• Online Access: http://plankt.oxfordjournals.org/cgi/content/short/20/9/1721; https://doi.org/10.1093/plankt/20.9.1721

Time series of North Sea cod, herring and zooplankton indicated a peak in biological production in the northern North Sea in the late 1960s and early 1970s. An increased recruitment of cod corresponded with high and increasing rates of fishing mortality. During the same time, the Buchan herring increased in abundance under stable fishing mortality. A synthetic analysis of CPR Area C2 ‘total Calanus ’ and ‘ Paracalanus/Pseudocalanus ( PP )’ reflected a declining abundance in the early 1970s. An analytic analysis of time series enabled the identification of large and small year classes of Calanus and PP. Large year classes of cod appeared to require large year classes of either PP or Calanus , but not both. Large year classes of cod appeared to be more associated with large year classes of PP rather than large year classes of Calanus. Simultaneous large year classes of PP and Calanus rarely occurred. A large year class of either Calanus or PP appeared to be required to produce a large year class of cod. However, the presence of a large year class of Calanus or PP did not guarantee a large year class of cod. The biological changes in the North Sea appeared to be coupled with a difficult to define climate signal involving changes in the windfield, deep convection in the north Atlantic, the great salinity anomaly, and changes in the vertical structure of the ocean off Bermuda.