MBES bathymetry data were collected using the ship's own Kongsberg EM 122 multibeam echosounder during the RV SONNE cruise SO306 CoWIO (Port Louis, Mauritius - Durban, South Africa). The primary goal of the cruise was to search for cold-water coral mounds in the West Indian Ocean. Data were recorded in the EEZs of Mayotte, Tanzania, Mozambique, and South Africa. These studies were endorsed as an UN Ocean Decade 2021-2030 of Ocean Science for Sustainable Development activity. This dataset includes 4 bathymetric grids produced based on the MBES data collected in the EEZ of Mayotte between 2024-08-11 and 2024-08-15. The grids represent 4 surveyed areas: 1) transit to the calibration area; 2) calibration area for the EM122 MBES north east of Mayotte; 3) main working area south west of Mayotte; 4) transits between the two working areas. Postprocessing of raw .all files was performed onboard by Evgenia Bazhenova and Alissa Bach using the QPS Qimera software. Data quality control included 1) verification that the SVP data were applied correctly based on the time and location; 2) blocking outer beams and in-turn data to ensure the best possible quality of the overlapping swaths, 3) manual point cloud cleaning if required. Depths measured by the MBES are reported in respect to the water level. Only static draft was taken into account. No tidal corrections were applied during the data acquisition or data postprocessing.

These data should not be used for navigational purposes.