Southern right whale population connections, trophic ecology and health on their South Georgia (Islas Georgias del Sur, SG/GS) feeding ground
J.A. Jackson, Gabriele Stowasser, Emma L. Carroll, Fredrik Christiansen, C. Scott Baker, Manuela Bassoi, Danielle L. Buss, Susannah Calderan, Ted Cheeseman, Martin A. Collins, Paul Ensor, Karina Groch, Ailsa Hall et al.
Southern right whales (Eubalaena australis) are regularly observed during the austral summer on the South Georgia (Islas Georgias del Sur, SG/GS) feeding ground. Here we report new results on the population connections, trophic ecology and health status of right whales on this feeding ground, combining results from summer expeditions conducted in 2018 and 2020. Our findings add to the evidence for the connection of this ground with the southwest Atlantic calving grounds: a whale photographed in SG/GS in 2020 matched a female sighted off Brazil in 2002 (as a calf), 2005 and 2007 (with a calf). We have also matched a whale photographed in SG/GS with one from the Antarctic Peninsula (the first time a match has been made between the two areas). Within the SG/GS photo-ID catalogue (77 identifications of whales from the left, right, both sides or overhead), 44 right whale images had sufficient coverage to be reviewed for kelp gull (Larus dominicanus) lesions (evidence of past visits to the Península Valdés calving ground in Argentina). Of these, eight whales (18%) had evidence of lesions and two had possible lesions. Visual assessments of whale health using vessel-based photographs primarily collected in 2017/18 and 2019/20 showed good levels of body fat, with all whales in good (55.7%) or medium (44.3%) body condition. Observed skin condition was poorer, with 46.2% of all assessable whales having poor skin condition, including the presence of lesions and sloughed skin. Quantitative measurements of body condition of five southern right whales in SG/GS in 2020, using drone photogrammetry, showed that both juveniles and adults were in similar condition to southern right whales measured on the Península Valdés calving ground in Argentina. Stable isotope analysis suggests the 6 females encountered at SG/GS in 2020 were likely feeding south of the Polar Front in the austral winter and early spring, while of the 3 males, two were feeding at lower latitudes and one south of the Polar Front. Overall southern right whales at SG/GS were in relatively good body condition in 2018 and 2020, with stable isotope patterns suggesting most of the whales encountered in 2020 had been feeding south of the polar front prior to visiting SG/GS.