Blue whales (Balaenoptera musculus)
Blue whales are the largest animals known to have inhabited the earth, reaching over 100 ft in length and weighing nearly 200 tons. They were heavily exploited by the whaling industry, and populations in every world ocean were reduced to mere fractions of their historical numbers. In the southern hemisphere, there are two subspecies currently recognized. One is referred to as the pygmy blue whale (B. m. brevicauda) (Ichihara 1966), characterized by a shorter body with different body proportions. Paradoxically, the pygmy blue whale actually weighs more than the typical or true blue whale (B. m. intermedia), due to the fact that its shorter body has greater girth. Although some mixing has been documented, pygmy blue whales tend to inhabit lower and middle latitudes, while the true blue whales spend their summers farther south, closer to the Antarctic continent. Although their morphological differences are readily seen in dead animals and they apparently have different vocalizations (McDonald et al. 2003),at-sea visual identifications are difficult.
There is a great deal of interest in knowing whether and how well blue whales in different parts of the world are faring. True blue whales in the Antarctic once numbered over 150,000 but in the 1970s were thought to number in the hundreds. Understanding current health of the population depends on making sure that what appears to be a slight recovery of true blue whales is not instead an increasing number of pygmy blue whales in what was traditionally the true's home waters. Obviously, we can't go killing them and hauling them onto decks to identify them, so we are developing genetic tools for use on wild populations. Our current research is focused on the determining the genetic differences between these two forms in the southern hemisphere, with the goal of determining diagnostic genetic tests for identification from simple biopsy samples (LeDuc et al. 2003).
LeDuc, R. G., Dizon, A. E., Goto, M., Pastene, L. A., Kato, H. and Brownell, R. L., Jr. 2003. Patterns of genetic variation in southern hemisphere blue whales. Paper SC/55/SH9 presented to the IWC Scientific Committee, 2003 (unpublished).
McDonald, M. A., Hildebrand, J. A. and Mesnick, S. L. 2003. Biogeographic characterization of blue whale song worldwide. Paper SC/55/SH7 presented to the IWC Scientific Committee, 2003 (unpublished).