Collection of cetacean sightings recorded during research cruise on Maria S. Merian collected during March 2023 along the Western Antarctic Peninsula. Data were collected whenever conditions for the dedicated line transect survey for cetaceans were not met. At least two observers were stationed on the observation deck, or, if conditions were harsh, on the bridge, logging all sightings of cetaceans. This data set includes all opportunistic observations of fin whales and aggregations, i.e. all observations made during station work or transit.