This is a technical report on the results from the 2021 aerial survey of southern right whales off southern Australia, specifically aimed at researchers and policy makers within the government. Collection of these data is a ‘high priority’ in the Australian EPBC Act Recovery Plan (Conservation Management Plan 2011-2021) to assess the current status of this threatened species and assess the effectiveness of federal and state management approaches that aim to facilitate this species’ recovery and range expansion. The whale count data from 2021 shows a significant decrease in overall sightings that has not been observed for over 13 years when compared to long term trend data for the population; last seen in 2007 (N = 286 individuals). The subsequent population estimate for the Australian ‘western’ subpopulation is 2,585 whales, which is also a significant decrease in estimated population size from 3,164 in 2019. The extremely low number of unaccompanied adults (N = 68) had the greatest impact on the overall number of sightings in 2020, and is the lowest number sighted since 1993 (N = 47). Previous surveys in 2007 and 2015 have been noted as years of low whale counts that had been deemed anomalous years, although the low numbers from this survey questions this and may suggest the 3-year female breeding cycle is becoming more unpredictable. Considerable inter-annual variation in whale numbers, and cycles in population growth, severely inhibits our ability to identify immediate threats to the population and strongly supports continued annual population surveys.