Assessment of the population structure of western North Atlantic right whales (Eubalaena glacialis) based on sighting and mtDNA data

Photoidentifications and 11 years of sighting data revealed that only two-thirds of the western North Atlantic right whale (Eubalaena glacialis) reproductive females took their calves to the Bay of Fundy, the only known summer nursery. Study of cow–calf pairs further indicated that female, and to a lesser extent male, calves were philopatric with respect to this nursery. To further examine population structure, mtDNA composite restriction morphs were determined for 150 animals (47% of the population). Using 11 restriction enzymes, three composite mtDNA morphs were identified. One morph was not found among reproductive females that brought all of their calves to the Bay of Fundy. In contrast, all three morphs were present, in the same relative frequencies, among males that were seen in the Bay of Fundy and those that were not. These findings support the hypothesis that this population may be divided into two subgroups, which are defined by their use of the Fundy nursery, and that males are generally less philopatric than females. Animals from both subgroups were seen on the southern Scotian shelf, where most right whale courtship behavior was observed. Hence, although segregated by nursery areas, the western North Atlantic right whales probably represent a single breeding population.