One of the terms we frequently use when describing right whale behavior is surface active group (SAG). A SAG has a fairly broad definition--two or more whales within a body length interacting at the surface--but typically, the SAG is comprised of one female and a number of males competing with each other in order to mate with her. Some SAGs are extremely active, with a lot of rolling and white water, whereas others are more sedate. The number of animals in a SAG can range from two or three to more than 40!
For years researchers presumed that the primary reason for a SAG was mating. However, conception is thought to take place in the winter (since gestation is about 12 months and right whales usually give birth between December and February), yet SAGs occur year round. Recent analyses of the composition and seasonality of these SAGs indicate that actually only about half of them include females able to reproduce. Thus, SAGs are not just for mating purposes.
Some have been documented to be all male, or all female, or all youngsters. Our colleague, Dr. Susan Parks from Woods Hole Oceanographic Institution, wrote a paper about SAG behavior in collaboration with Aquarium researchers (see below). She hypothesizes that, in addition to conception, SAGs may serve a variety of different roles including practice, play and social bonding.
Studying the behavior of marine mammals such as right whales is much more difficult than that of terrestrial species, because we get just a glimpse of these animals when they're at the water's surface. But the long-term photo-identification aspect of the Aquarium's program has enabled researchers to answer some very basic and important questions. The researchers found themselves in the right place at the right time and recorded fantastic videos of SAGs here and here.
Top photo: Taken by Monica Zani in the Southeast U.S.
Bottom photo: A typically boisterous SAG in the Bay of Fundy. Photo taken by Moira Brown
Parks, S. E. et al. 2007. Occurrence, Composition, And Potential Functions Of North Atlantic Right Whale (Eubalaena glacialis) Surface Active Groups. Marine Mammal Science 23(4): 868-887.