First direct observation of a successful southern right whale (Eubalaena australis) birth in South African coastal waters

Abstract

Southern right whale females (Eubalaena australis, hereafter SRWs) usually migrate between higher latitudes where they forage in summer to coastal areas at lower latitudes where they give birth and nurse their young in winter (Best, 2000). In South Africa, the SRW calving season extends between late June to late October, with a birthing peak in August (Best, 1994). This predictable coastal presence has enabled population monitoring since the late 1960s by means of annual aerial surveys (e.g., Best, 1990;Best et al., 2001). In addition to monitoring population recovery postwhaling, these long-term surveys have also allowed for the observational assessment of reproductive parameters. As such, the age at first parturition in the population was estimated at 8 years with an average calving interval of 3 years and an estimated gestation length of 12-13 months (Best, 1994;Best et al., 2001). However, despite these long-term research efforts, very little is known regarding the actual birthing event in SRWs (Best, 1994). Three accounts of possible SRW births off the coast of South Africa have briefly been discussed in Best (1970) and Best (1981) but they all relate to anecdotal evidence from distant shore-based observations. Documentation of SRW births is equally rare across calving grounds throughout the southern hemisphere. In 2012, an unsuccessful birth was documented in Argentina (Península Valdés) from a whale watching vessel and reported in Sironi et al. (2019). The authors suggested that there were a few possible factors indicating that this was an abnormal parturition including the repeated protrusion and withdrawal of the calf, lengthy time-period before full expulsion of the calf, and resighting of the female without a calf (Sironi et al., 2019). However, despite the increasing boat-based presence around SRWs, mostly in the form of whale-based tourism, close and detailed observation of a successful birth has, to our knowledge, never been directly observed and documented. Therefore, here we report the first documented successful SRW birth observed along the South African coast, supplemented with photographic evidence. † Deceased.