Female southern right whales Eubalanena australis: Are there reproductive benefits associated with their coastal distribution off South Africa?

Predictability in both meso- and microscale distribution of southern right whale Eubalaena australis females off the coast of South Africa is attributed to maternal philopatry, as well as favourable environmental conditions (calm water, generally shallow sloping, sedimentary sea bed) conducive to reduced energy consumption and a lowered risk of injury for both cows and calves. Spatial differences in reproductive success were compared between favoured (nursery) and non-favoured (non-nursery) areas and related to environmental differences in those areas. Reproductive success was inferred from analysis of calving intervals (3 yr = successful, 2 and 4 yr = unsuccessful; n = 808 calving events). Resighting rates as well as differences in distribution between experienced cows (3 or more calves) and inexperienced cows (1 or 2 calves) were also analysed. Less experienced cows were found to have significantly more unsuccessful calving intervals than experienced cows. No relationship was found between calving success and spatial distribution using calving interval analysis. Significant spatial differences in stranding rates of neonatal calves strongly suggest higher rates of calf mortality in areas dominated by non-cows, independent of environmental conditions. Social structure within wintering grounds was concluded to be more important than previously thought and potentially as important as environmental conditions for calf survival.