European Ocean Biodiversity Information System

Each year, three observers take place on board the vessel “Thalassa” to record sightings of seabirds, marine mammals, large fish and fishing boats, from dawn to dusk. Following distance sampling methods, visual censuses are made by two observers (while the third observer is resting) from the upper platform of the boat (min. 14m above the sea level). They are placed on each side of the deck, looking ahead for marine predator with an angle of 180°. For each sighting, the species and the number of individuals are recorded, as well as the behaviour, distance and angle (upon request). Purpose: One of the main advantages of this survey lays in its ecosystemic approach, which provides information on all the components of the food web (from planktonic organisms to predators) as well as data on the environmental parameters (sea surface temperature, salinity…). Interactions between prey and predators are complex in marine ecosystems, which are submitted to strong spatio-temporal variations. Thanks to ecosystem-based surveys, observed distributions and densities of marine predators can be related to the occurrence of their prey, providing to scientists and managers a better understanding of the marine ecosystems structure. Supplemental information: [2017-01-05] sighting records in 2016 were appended. Time and group size of the sightings are not available online. They may be released upon request.