A second example which involves species conservation issues and improved understanding of population biology is for the humpback whale ( Megaptera novaeangliae). Like turtles, most of the ``great whale'' species have undergone phenomenal losses due to human hunting, particularly prior to international efforts to protect them. The global population of humpback whales was especially impacted by whaling, having been reduced to an estimated 5% of their natural size by the early 1960s [ Chittleborough, 1965]. This dangerously small population may be at risk, even after it is protected, due to reduced genetic variability. Molecular-genetic analysis of individuals from different geographic regions can be valuable for determining remaining genetic variation within the global population.
Like most baleen whales, the humpback whale migrates annually between summer feeding grounds in temperate and near-polar regions and winter breeding grounds in shallow tropical regions. In the North Pacific Ocean, for example, this species has two distinct migration routes between Hawaii and Alaska, and between Mexico and just offshore of the Farallon Islands, California [e.g., Baker et al., 1990]. Important questions in terms of genetic diversity and conservation of this species are, do these different migration routes represent different populations, or, do individual whales transfer between routes so often that they can be considered one global population?
Baker et al. [1990, 1993] addressed these questions by analyzing mtDNA patterns of humpback whales collected at the four terminal migration locations in the North Pacific mentioned above, and several locations in the North Atlantic. Individuals from Alaska and Hawaii had similar mtDNA types, which differed from those occurring in central California or Mexico. Thus, populations along these two migration routes are genetically distinct and need to be managed and preserved as separate entities. In fact, Baker et al. [1990, 1993] found substantial genetic variation among individual humpback whales sampled throughout the world's oceans, indicating that the prompt international efforts to stop harvesting them may have prevented major inbreeding depression.