The observation of ecosystems by Ifremer's Fisheries Information System (SIH) is based on a network of sea cruises. It aims to assess the state of stocks of the various species fished in France and Europe. It also enables the characterisation of the marine ecosystem in which the populations evolve. 23 scientific cruises take place each year at sea, enabling data to be collected for more than 30 years for the oldest. Thanks to the use of standardised fishing gear, the data acquired each year on board scientific vessels or professional fishing vessels contribute to the calculation of the index of abundance, with thousands of fish taken during timed trawls. The fish are measured and their age is assessed by measuring their otoliths (small bones located in the inner ear of the fish).