The Atlantic mackerel (Scomber scombrus) is a gregarious pelagic fish emblematic of the North Atlantic, the English Channel, and the Mediterranean Sea. Lacking a swim bladder, it is forced to swim constantly to maintain buoyancy, which gives it excellent swimming capabilities. Its streamlined body, recognizable by its blue-green back adorned with sinuous dark chevrons and its silvery flanks, features five characteristic finlets before the caudal fin. As a migratory species, it traditionally alternates between a demersal winter phase, marked by fasting in deep waters, and a spring and summer pelagic phase dedicated to planktonic feeding and reproduction.

Mackerel migration is intimately linked to water temperature, a decisive factor for its survival and movement. Historically, mackerel likely do not frequent waters with temperatures below 8.5 °C. In the 1970s, environmental changes and warming waters led to a major shift in behavior: a large part of the western stock, which previously distributed itself differently, began overwintering in the Western English Channel. This phenomenon marked a break from previous migratory patterns, illustrating the species' sensitivity to thermal fluctuations. By 2012, this trend was confirmed, with climate change now pushing mackerel to migrate further north toward colder areas to find a suitable habitat, rendering old quota allocation agreements obsolete as the populations are no longer located where the treaties had initially positioned them.

This forced modification of migratory routes has had dramatic consequences for the species' sustainability, exacerbated by failing international governance. In the absence of a global agreement following recent developments, states have set quotas unilaterally, leading to massive overfishing. The resource has collapsed, with the biomass of reproductive-age individuals halved over five years, reaching a critical threshold. The renewal of generations is also threatened by a significant drop in the number of young mackerel. Faced with this situation, scientists are sounding the alarm: to hope for stock recovery, drastic reductions in catches are necessary. The case of the mackerel, trapped between the shift in its natural habitat and uncoordinated fishing pressure, serves as a warning for the management of migratory species in the context of global climate change.