This dataset was collected during PS119 during a dedicated distance sampling survey for cetaceans in the Southern Ocean conducted on board of Polarstern during the austral summer 2019 (25-04-2019 - 21-05-2019). Effort related sighting data were collected along the ship track of R/V Polarstern to infer density distribution of southern hemisphere fin whales. Surveys were conducted whenever wheather and ship operations permitted. Surveys were conducted with 2 observers and one data logger from the crow's nest at ~ 29m ASL. Positions were logged every 4 seconds using a dedicated survey software and all cetacean sightings were recorded upon detection. All changes that may impact detection probability of cetaceans were noted as described by the observers. This dataset contains all cetacean sightings recorded on track, including species, group size and effort related data including position (lat / lon) and datetime (utc format). All cetacean sightings were identified using binoculars (if possible) and comprise the number of animals in the group. Groups were defined as animals in close proximity at no more than two body lengths apart (not to be compared with e.g. acoustic groups that may stretch across hundreds of kilometers). All detections were made using naked eye, binoculars were only used for species identification.