IBTS surveys (International Bottom Trawl Survey) are carried out within an international framework. Main countries bordering the North sea participate to it according to the European Community regulations (EC N°1543/2000 and N° 1639/2001) which specify that countries from E.U. must carry out surveys at sea in order to assess abundance and stocks distribution, independently of commercial fisheries data.

The first aim of the IBTS survey is to have a diagnosis on the main commercial fish stock and to calculate abundances index by age for these species. This survey started in the 1970's and was progressively standardised. Since the 1980's, a common protocol and material is implemented and used by all participants. In order to compute an index for herring and sprat larvae (groups 0), each participating vessel operates with a MIK net during the night (Methot Isaac Kidd).

Since 20 years, the southern part of the North sea is allocated to the French vessel and, since 2007 the Eastern Channel is integrated to the whole sampled area. Because of interactions and circulation of stock between these two areas are important, Eastern Channel is often associated the North Sea for stock assessment. For example, Herring is exploited all the year in the North sea and comes into the Channel during the end of the year (November-December) for reproduction. Thus, sampling this area during the IBTS survey provides a more complete assessment of larval indices for this species. As part of an ecosystem approach, a complementary work is done to study most biological compartments, from phytoplankton to top predators. For example, the Continuous Underwater Fish Eggs Sampler device (CUFES) is used to study fish spwaning areas. In the same way, the distribution of phytoplanktonic, zooplanktonic and macroinvertebrates communities is also assessed. Finally, additional samples are collected since 2015 for the Marine Strategy Framework Directive (MSFD).