This dataset was collected during PS112 during a dedicated distance sampling survey for cetaceans in the Southern Ocean conducted on board of Polarstern during the austral summer 2018 (23-03-2018 - 24-04-2018). Effort related sighting data were collected en-route using helicopter flights planned ad-hoc based on the current position of R/V Polarstern to infer density distribution of southern hemisphere fin whales. Surveys were conducted whenever wheather and ship operations permitted. One observer was seated on the port side of the helicopter and the data recorder was seated in the copilot seat on the port side. 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. Surveys were conducted at an altitude of 600ft at 100 kts and seastates less than 3 Bft.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 confirmed if possible (pending on fuel limitations and accessibility of the cetacean group) 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).This data has been used in a number of publications and results of these analysis has been mentioned in various media outlets.