North Atlantic and southern right whale social interactions and sexual behavior have been studied for decades. Understanding whale mating systems can inform about many aspects of their biology and even their anatomy. Right whales have a polygynandrous mating strategy where females and males mate with multiple partners within a breeding season. It is hypothesized that this promotes sperm competition among males and likely explains the large testis-to-body-size ratio in Eubalaenids. Surface active groups (SAGs) characterize mating behavior in North Atlantic and southern right whales, where two or more animals are at the surface with frequent physical contact. Observations of copulation in SAGs have led to the hypothesis that conception is the primary function, with females practicing a mating strategy where the chance of conception with the largest and likely healthiest male would be maximized. Right whales produce their entire acoustic repertoire of known calls while in SAGs and sounds are thought to serve a social communication function. In the North Atlantic, surface active behavior is seen in all habitat areas and in all months of the year in which right whales are sighted. SAGs tend to increase in size and vigor as the mating season approaches, resulting in spectacular and highly energetic courtship activity with group sizes numbering 30 animals and more; however, the whereabouts of any breeding ground is unknown. On southern right whale calving grounds, mother-calf pairs use relatively shallow waters along the coastline, and SAGs tend to occur farther from shore: calving and mating occur in winter in largely the same habitat areas. Analyses of seasonal timing and group composition of individually identified animals within SAGs suggest that they may serve multiple other roles, since conceptive and non-conceptive groups have been revealed. SAGs often include pregnant females, juveniles, and occasionally calves. Some groups consist of exclusively same sex individuals. It has been hypothesized that, in addition to conception, SAGs may also provide opportunities for right whales to socialize, play, learn, practice mating, and identify potential future mates.
