European Ocean Biodiversity Information System

The North Sea cod and plaice egg surveys have been conducted in 2004 and 2009 and will be continued in 2013 alongside the MIK herring larvae sampling during the IBTS survey.

The surveys were originally directed at cod and plaice, but also supply data of other winter spawning North Sea fish. The surveys are conducted with Gulf III or VII plankton torpedo’s, Bongo nets or CUFES. With the Gulf’s and Bongo’s double oblique hauls are conducted through the water column till 5m above the sea floor or a maximum of 200m depth. The CUFES sampling is a continues sampling at 5m depth. The mesh size of all sampling equipment is 280 μm. During the sampling temperature and salinity are measured. Flowmeters are used to measure the amount of water filtered while sampling.

The database contains the haul information data, position, time , duration, water volume, depth, temperature and salinity. Eggs and larvae in the samples werecounted. All eggs >1mm were measured and identified to species were possible. Eggs <1 mm are counted and in 2004 measured and identified as well. There is large overlap in size some gadoids, including cod, and other species, thus identification by eye is not possible. For these, genetic analysis was used to identify the species. All eggs that are measured and identified were also staged following the stage descriptions in Appendix A. Larvae in the samples were identified to species, measured and development stage assigned.