The extent to which the assumptions underlying line transect sampling are satisfied in shipboard surveys of crabeater seals hauled-out on the Antarctic pack-ice is examined. Crabeater seals showed little movement in response to the approaching ship. Movement away from the ship by seals close to the ship’s track was partially responsible for a relative lack of sightings close to the transect-line, but otherwise had little effect on the sighting histogram. Minor deviations from the transect direction to avoid running over seals violated the assumption of uniform distribution of groups, and contributed to a relative lack of sightings, close to (