International Bottom Trawl Survey (IBTS2019-Q1). French cruise report

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. have to carry out surveys at sea in order to evaluate abundance and stocks distribution, independently of commercial fisheries data. The first target 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 years 70’s and gradually standardised. Since the years 80’s, a common protocol is implemented and used by all participants. The same fishing gear and the same working methods are used. In addition, to calculate an index for herring and sprat larvae (0 groups), each participating vessel operates with a MIK net during the night (Methot Isaac Kidd). For 20 years, the southern part of the North Sea has been allocated to the French vessel and since 2007, the Eastern Channel has been integrated to the whole sampled area. As interactions and circulation of stock between these two areas are important, Eastern Channel is often associated the North Sea for stock assessment. Herring for example which is exploited all the year in the North Sea comes into the Channel during November and December for reproduction. More precise information on larvae indices will be obtained when this area is sampled. In order to study the whole marine ecosystem of the North Sea and English Channel, some additional studies are carried out during the Survey on the R/V Thalassa. For example, the Continuous Underwater Fish Eggs Sampler device (CUFES) is used to study fish spawning areas. Abundance and distribution of the winter planktonic community (phyto and zoo plankton) and a monitoring study on the structure and distribution of the benthic macroinvertebrates community are also carried out. At last, more samples are done for the Marine Strategy framework since 2015.