Résumé
Here we present an approach to identify partners at sea based on fishing
track analysis, and describe this behaviour in six different fleets: 1) pelagic
pair trawlers, 2) large bottom otter trawlers, 3) small bottom otter trawlers,
4) mid-water otter trawlers, all operating in the North-East Atlantic Ocean, 5)
anchovy purse-seiners in the South-East Pacific Ocean, and 6) tuna
purse-seiners in the Western Indian Ocean. This type of behaviour is known to
exist within pelagic pair trawlers. Since these vessels need to be in pairs for
their fishing operations, in practice some of them decide to move together
throughout their whole fishing trips, and others for only a segment of their
trips. To identify partners at sea, we used a heuristic approach based on
joint-movement metrics and Gaussian mixture models. The models were first
fitted on the pelagic pair trawlers and then used on the other fleets. From all
of these fisheries, only the tuna purse-seiners did not present partners at
sea. We then analysed the connections at the scale of vessels and identified
exclusive partners. This work shows that there are collective tactics at least
at a pairwise level in diverse fisheries in the world.