The Arab herders that we followed travel over 100kms from their "homeland" in the Sahel to the shores of Lake Fitri, their "host zone" where sedentary farmers reside, organized around a sultanate. In the face of the climatic changes affecting the Sahel, these herders have been led to modify their routes and mobility schedule. More and more of them are attracted to this wetland; they tend to come earlier, stay longer each year and enter the lake more. In the course of a year, they therefore have to cross different ecosystems (between desert and wetland areas), negotiate their presence with groups to which they are more or less linked (between herders in the north/on foreign territory in the south), and deal with the strong seasonality of resources (abundant in the rainy season, more scattered at the beginning of the dry season, and then very concentrated at the lake before they run out). The exchange of livestock is one of the important adaptation mechanisms of these nomadic pastoral systems: the sale of livestock allows people to modulate the size of their herd, to make partners and support their relatives, and to quickly free up the money needed to manage the numerous expenses. Thanks to environmental monitoring since the great droughts of the 1970s and 1980s, a good knowledge of the multifunctionality of the lake and precise surveys of animal exchanges in two herders' camps since 2020, we will describe these different ways of circulation during the year and present the recent evolutions. We will show that these exchanges are at the heart of the concerns of the herders: it is a question of being able to give up enough animals to face these seasonal challenges, without threatening the viability of their herd; a balance not always easy to maintain.
