Population identity, site-fidelity, movement ranges and preliminary estimates of abundance of southern right whales in the Antarctic Indian sector inferred from genetic markers

Baleen whales are important components of the Antarctic marine ecosystem as ‘sea-based’ top predators. Information on their distribution, movement and abundance trend is important as input data for ecosystem modelling studies. Genetic analyses were conducted to investigate the population identity as well the individual identity of southern right whales distributed in summer in the Antarctic Indian sector. The latter analysis was conducted to assess their site-fidelity, sex-specific ranges and abundance based on ‘mark-recapture’ methods in the Antarctic Indian sector (i.e., between 80°-135°E and south of 60°S). In total, 157 biopsy samples were collected as skin biopsies from free-ranging whales during fourteen summer surveys. The DNA was extracted from each biopsy sample, sequenced for 381 nucleotides of the mtDNA control region, genotyped at fourteen microsatellite loci, and the sex determined by the presence of a Y-chromosome specific locus. The mtDNA analysis suggested that whales in the Antarctic Indian sector in summer are closely related to the Australian calving ground. Eight incidences of individual matching (‘mark-recapture’) were detected (four males and four females). Individual matching by multi-locus genotypes was supported by mtDNA, sex determination, and in two cases where pictures were available, by photo-identification. These eight re-captures suggested that individual whales tended to return to the same location in the Antarctic Indian sector in subsequent years. The average longitudinal dispersal ranges were 13°06’ and 7°15’ in males and females, respectively. The time span between the ‘mark’ and the ‘recapture’ ranged from 3-13 years with an average at 7.3 years. Preliminary application of a ‘mark-recapture’ method based on an open population model, resulted in abundance estimate trend in the Antarctic Indian sector similar to those obtained using sighting survey data and the Line Transect Method in the same sector and similar period. However differences were observed in some years, which suggest that some of the assumptions used in the genetic ‘mark-recapture’ method should be further considered in future.