Winter is cool: spatio-temporal patterns of the squat lobster Munida gregaria and the Fuegian sprat Sprattus fuegensis in a sub-Antarctic estuarine environment

In the sub-Antarctic waters of southern South America, two species that form conspicuous pelagic aggregations are considered both potential fishery resources and ecologically important: the Fuegian sprat Sprattus fuegensis and the squat lobster Munida gregaria. Here, we estimate spatio-temporal patterns of the relative abundance, distribution and potential areas of overlapping of M. gregaria and S. fuegensis in the Beagle Channel. Acoustic data were collected from 18 surveys conducted between 2009 and 2016 in the Beagle Channel. Our observations on the pelagic aggregations revealed that M. gregaria swarms and S. fuegensis schools occurred along the channel throughout the year. However, the occurrence of S. fuegensis was more evident in the inner part of the channel during the winter. There was a negative relationship between the relative abundance of squat lobsters and Fuegian sprats throughout the year. This interaction may result from spatial competition associated with resources, particularly in summer. The vertical distribution and morphology of aggregations of both species showed seasonal differences. Specifically, schools of Fuegian sprats were typically pelagic in summer, whereas in winter they were bigger and associated with the bottom layer. This change could be associated with a seasonal change in the oceanographic regime of the Beagle Channel. The information presented here is necessary to understand processes in a context of possible opening of fisheries targeting these two species that have key ecological roles in this sub-Antarctic ecosystem.