Population status of Ross Sea killer whales (Orcinus orca, Type C) in McMurdo Sound, Antarctica, based on photo-identification studies

We studied Ross Sea killer whales (RSKWs; Orcinus orca, Antarctic type C), a fish-eating ecotype, in McMurdo Sound, Antarctica, during 7 seasons, over a 14-year period from 2001/02 to 2014/15. Using photo-identification methods, we identified 352 individual RSKWs in the Sound and up to 175 there annually. Despite high turnover of different whales between years, we used a Bayesian mark-recapture approach to identify a seasonal ‘resident’ population with an average annual abundance of 55 individuals (95% probability = 44-68) that exhibited strong inter- and intra-annual site fidelity, with individuals resighted over 2-14 years. Contrary to recent reports that commercial overfishing of Antarctic toothfish (Dissostichus mawsoni) may have led to a marked decline RSKW numbers in the southwestern Ross Sea, our analysis suggests that at least the resident killer whale population in McMurdo Sound is stable with the average annual estimated number of deaths (= 2.4, 95% probability = 1.2-4) being balanced by the estimated number of recruits (= 2.6, 95% probability = 0.9-4.4).