Après de multiples cycles au cours des siècles passés, la récolte des algues dans le Finistère se renouvelle et s’inscrit comme une filière d’avenir. Au-delà des changements socio-économiques, elle se confronte aux problématiques actuelles de conservation de la biodiversité et de partage de l’espace maritime. Comment dès lors concilier activités anthropiques et préservation du milieu ? La démarche ethnoécologique mobilisée, interroge la gestion des ressources par les populations locales au travers de leurs engagements — pratiques, savoirs locaux et représentations. L’objectif de la thèse est donc double : comprendre les dynamiques des engagements des collecteurs d’algues ? Et comprendre comment ils sont mobilisés et ils évoluent face aux enjeux actuels ? Grâce à une enquête ethnographique et aux méthodes de l’ethnoécologie, nous avons interrogé les cadres scientifiques, sociaux et administratifs de manière diachronique pour saisir le contexte et les enjeux. Ensuite, nous avons questionné l’identité des collecteurs au travers des « statuts administratifs », puis de cinq profils émergeant des données. Cette diversité des formes d’engagement se retrouve dans les perceptions sensorielles mobilisées lors de la récolte, dans les systèmes de classification vernaculaires des algues et dans l’appréhension de l’espace. L’analyse de ces trois dimensions révèle un ensemble très riche de savoirs « intimes », « incorporés » et « situés » indissociables des techniques, sur les algues, le milieu aquatique et les dynamiques de l’écosystème. Différents éléments au travers des savoirs et des représentations éclairent les conflits et illustrent l’influence des scientifiques et des industriels sur les collecteurs. L’aléa climatique de l’hiver 2013-2014, en impactant la ressource algale, a contraint les collecteurs d’algues à s’adapter. Il a révélé les jeux d’acteurs dans les filières et la nature composite, voire hybride des engagements, premier pas vers une cogestion. / After several cycles over the course of past centuries, seaweed harvesting in Finistere is once again experiencing a revival and emerging as a promising sector. Beyond socio-economic transformations, it is also faced with current issues of biodiversity conservation and the sharing of maritime space. How can human activity and preservation of the environment be reconciled? The mobilized ethnoecological approach looks at resource management by local communities through their engagement - practices, traditional ecological knowledge, and representations. The aim of this thesis is thus twofold: understanding the dynamics of seaweed harvesters' engagement, and understanding how they mobilize and cope with current issues. Through ethnographic survey and ethnoecological methods, the scientific, social, and administrative frameworks were investigated diachronically to understand the context and the issue. The identity of the collectors were studied through both 'administrative statuses' as well as five profiles that emerged from the data. This diversity in forms of engagement is reflected in the sensory perceptions mobilized during harvesting, in the vernacular classifications of seaweed, and in how space is apprehended. The analysis of these three dimensions reveals a rich body of 'intimate', 'embodied', and 'situated' knowledge that is inextricable from practices relating to seaweed, aquatic environments, and ecosystem dynamics. Finally, various elements across knowledge and representations shed light on conflicts and illustrate the influence of science and industry on collectors. The climate event that took place during the winter of 2013–2014, for example, left an impact on seaweed resources and forced collectors to adapt. It revealed the interplay between actors of the various sectors and the composite (or even hybrid) nature of their engagement, a first step towards co-management.

As living beings, seaweeds exist at the periphery of people’s awareness, and not much is known about what they mean to people, and the relationships we can have with them. They are useful, versatile commodities, and multitask as foodstuffs for people and other beings, as sources of biofuel and medicinal compounds, and the list goes on... but, what else? This work seeks to shed light on the kinds of relations that people can have with seaweeds when relationships of use are purposefully bracketed out, in order to understand their social and symbolic worlds. To this end, during the months of November through January, the author discussed the perceptions of seaweeds with the neighbours of the area of Loch Hourn, a sea-loch (fjord) in the western seaboard of the Scottish Highlands, and some other nearby townships. The present study interlaces participant observation nuanced by the winter and the weather, and interviews, to explore how, through relations of biosociality, companionship, awareness and interanimation of the environment, alternative configurations of knowing, Gaelic tradition, symbolism, and hope, seaweeds embody different aspects of the meaning of‘sanctuary’.