The difficult construction of a trust relationship between professional, scientific fishermen and managers in relation to an unknown phenomenon. The example of liga on the Basque coast.

At the end of the years 2000, the professional fishermen of the Basque coast have to launch alarm. The presence of liga increases (frequency and duration of the episodes). The liga is a gelatinous and sticky substance which sticks to the nets, prevented the capture of fish and obliges to clean hardly fishing tackle. Research program LIGA (2013-2016) will finish in a few months. It will specify the physicochemical nature of this substance. But the problems do not stop with the questions biophysics purely. Which is the origin of this substance? Which problems its presence poses? How are its impacts, its possible dangerousness perceived? How the people concerned evaluate do to them proper capacity to suffer this damage, to act and to adapt? Who is responsible for his development? Who is responsible for his management? All these questions explain why a socio-economic shutter was carried out. We conducted a survey based on semi-directing interviews (winter 2015-2016) in order to better know the social representations of the various actors concerned with this phenomenon. This knowledge is impossible to circumvent because the representations are the base of the “public opinions”. In this communication, we will have the great results of this study. We will particularly endeavour to describe the relation fishermen/scientific world/field of the action and the public administration. Although the analyses are still in hand, we observe that the topics of the knowledge, the scientific knowledge and its diffusion are central in the construction of a trust relationship between the actors of the territory. However, for the time being, the questioned professional fishermen evoke in a generalized and marked way a lack of transparency, slowness, the existence of hidden challenges, pressures. One observes at the same time an internal problem of coherence of their speech and several levels of contradiction. It will be seen that it is not enough to advance relevant elements from a scientific point of view, by definition “neutrals”, even if one can that it is never completely true, to be heard. Various brakes are initially with raising. Beyond the case of the phenomenon liga, recent and specific to the Basque coast, the set of themes of the knowledge sharing, its co-construction is relevant whatever the subjects of studies since the challenges observed on the littorals mix the economic questions and environmental