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19091
Open
SC/68C/SH/18
Population trend in right whales off southern Australia 1993-2020
Smith, J.N., Kelly, N., Double, M. and Bannister, J.L.
IWC
2021
Annual aerial surveys of southern right whales have been conducted off the southern Australian coast, between Cape Leeuwin (W.A.) and Ceduna (S.A.) over a 28 year period between 1993 and 2020, to monitor the recovery of this species following commercial whaling. We conducted an aerial survey of southern right whales between the 20th and 24th August 2020, to continue these annual series of surveys and inform the long-term population trend. The comparable count for the 2020 survey utilised the maximum count for each leg and incorporated a correction for the unsurveyed area between Head of the Bight to Ceduna due to the inability to cover whole survey as a result of COVID-19 restrictions between State borders. This resulted in 384 individuals, consisting of 156 cows accompanied by calves of the year and 72 unaccompanied adults. Of these, 126 images of individual whales have been selected for photo-identification matching. This is 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 to 2,585 in 2020. 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, makes it difficult to detect consistent and reliable changes in abundance from one year to the next, or even over longer periods of time. This severely inhibits our ability to identify immediate threats to the population and strongly supports continued annual population surveys.
