Gender related structure in blue whale ( Balaenoptera musculus ) pairs from eastern Canadian waters

Abstract:

Studies of blue whales ( Balaenoptera musculus ) were carried out in the Gulf and Estuary of the St. Lawrence during the months of June to October, from 1979 to 1998, with an average effort of 128 days per season. A photographic-identification catalogue of 350 individual blue whales was compiled, and 160 skin biopsies were taken. Gender was determined through analysis of sets of primers specific to either the ZFY or ZFX sequence found on the sex chromosome found in the skin samples and resulted in the sexing of 113 individuals. Blue whales were predominantly observed singly or in pairs, which were made up of a lead animal and a companion individual following to the left or right, within a body length. We observed 288 pairs of blue whales, divided into three categories: pairs for which we knew the gender of both animals (59), pairs for which we knew the gender of one animal (141), and pairs for which we knew neither individual's gender (88). Results from analysis of pairs where both animal's gender was known, indicated that 66% of blue whale pairs were mixed. Analysis also revealed that females lead 94% of pairs where the gender of both individuals was known. Females lead 77% of the pairs, where only the gender of females was known, while in pairs where only the males were determined, males were following 84% of the time. We found that pairs were observed with greater frequency as the season progressed from spring to fall. Because reproduction is thought to take place in late fall and winter in this species, such pairings in blue whales may have a significant bearing on their reproduction. It is likely that by maintaining a rear flanking position males can keep track of females more easily and defend their position against intruding males - similar behavior to that found in humpbacks on their winter breeding grounds.

Sears, R., P. Palsbøll, C.L. Berchok, T. Doniol-Valcroze, and C. Ramp. 1999. Gender related structure in blue whale ( Balaenoptera musculus ) pairs from the North Atlantic . Oral presentation to the 13th biennial conference on the Biology of Marine Mammals, Maui, Hawaii, November 28 – December 3, 1999.