Results of the spring 2004 North Sea ichthyoplankton surveys. The distribution of fish eggs and larvae from the international ichthyoplankton survey
A key recommendation of the meeting of scientific experts, which accompanied the Fifth International Conference on the Protection of the North Sea, 20-21 March 2002, Bergen, Norway, was that there should be regular monitoring of the spawning grounds of important commercial fish species. Up to this point there had never been a comprehensive survey of spawning grounds covering the whole North Sea. The problem was seen as particularly pressing in relation to cod, where a lack of up-to-date information hampered the design of suitable protection measures. In response, ICES set up a planning group (PGEGGS) to review whether a complete North Sea survey targeting eggs and larvae would be feasible. Planning took several years owing to the complex international nature of the problem, but in late 2003 and early 2004, ichthyoplankton surveys covering the whole North Sea were conducted to comprehensively assess the spawning areas of cod and plaice. The survey itself was titled PLACES (Plaice and Cod Egg Survey) to distinguish it from the work of the planning group (PGEGGS). A group of international research institutes took part from England, the Netherlands, Germany, Denmark, and Norway. Subsamples of eggs that were “cod-like” in appearance were presorted from samples at sea and preserved in ethanol for analysis using species-specific genetic probes. The remainder of each sample was preserved in formalin, and the ichthyoplankton were identified later, using traditional visual methods. A full account of the material and methods used, plus initial results of the distributions of cod and plaice spawning, can be found in Fox et al (2005a). Details of the molecular methods used to identify cod-like eggs are reported in Taylor et al. (2002). For the cod-like eggs, proportions were assigned, based on the genetic results at each station, but these results are not presented here. This report presents the distributions and abundances of eggs and larvae of the other species identified from the survey series.