Cetacean Systematics and Taxonomy

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An integral part of managing and conserving cetacean populations is understanding their taxonomy. At one level, this means having a good idea of the numbers of species that are extant. This, in turn, requires an understanding of the geographic boundaries morphological differences between species, which is not always evident for closely related or very similar looking species. For example, Perrin's work on dolphins of the genus Stenella  (Perrin 1975, Perrin et al. 1981, Perrin et al. 1987) proved invaluable for conservation efforts on these species, which include those entangled in tuna purse seines in the eastern tropical Pacific. More recently, genetic research on Bryde's whales (Balaenopteraedeni/brydei; Wada and Numachi 1991, Yoshida and Kato 1999, LeDuc and Dizon 2002, Kato 2002) provided evidence that there are at least two species of Bryde's whales, whereas most taxonomies had only recognized one. The pygmy Bryde's whale, which has now been documented from various locales in the tropical Indo-west Pacific, has now been added to modern cetacean species lists. However, there is still much to learn about the Bryde's/sei whale complex. Ongoing genetic work, in conjunction with morphological and ecological research, will focus on better delimiting the geographic boundaries of the pygmy Bryde's whale, deciding what scientific name it and the "ordinary" Bryde's whale should bear, and determining the paterns of relatedness with other populations of other whales in the complex. A similar focus on killer whales (Orcinus orca) is of great importance for their conservation.

perrin.gifAt a higher taxonomic level, determining the patterns of relatedness among species and genera can also provide valuable insights. For example, molecular phylogenetic analysis of the dolphin family Delphinidae (LeDucet al. 1999) provided evidence that two genera of dolphins (Stenellaand Lagenorhynchus) were artificial assemblages of unrelated species. Besides helping with our understanding of dolphin evolution, such findings also have implications for comparative studies of dolphin ecology. In other words, when comparing biological characteristics of closely related species, one needs to know who the closely related species are.

Kato, H. 2002. Bryde's whales Balaenopteraedeniand B. brydei. pp 171-177 in W. F. Perrin, B. Wursig and J. G. M. Thewissen (eds.) Encyclopedia of Marine Mammals. Academic Press, San Diego. 1414 pp.among the delphinid cetaceans based on full cytochromeB sequences. Marine Mammal Science 15:619-648.

LeDuc, R. G. and Dizon, A. E. 2002. Reconstructing the rorqual phylogeny: with comments on the use of molecular data for systematic study. pp 100-110 in C. J. Pfeiffer (ed.) Molecular and Cell Biology of Marine Mammals. Kreiger Publishing. Malaber, FL. 427 pp.

Perrin, W. F. 1975. Variation in spotted and spinner porpoise (genus Stenella) in the eastern tropical Pacific and Hawaii. Bulletin of the Scripps Institution of Oceanography. University of California 21. 206 pp.

Perrin, W. F., Mitchell, E. D., Mead, J. G., Caldwell, D. K. and van Bree, P. J. H. 1981. Stenellaclymene, a rediscovered tropical dolphin of the Atlantic. Journal of Mammalogy 62:583-598.

Perrin, W. F., Mitchell, E. D., Mead, J. G., Caldwell, D. K., Caldwell, M. C., van Bree, P. J. H. and Dawbin, W. H. 1987. Revision of the spotted dolphins, Stenella spp. Marine Mammal Science 3:99-170.

Wada, S., and Numachi, K. 1991. Allozyme analyses of genetic differentiation among the populations and species of Balaenoptera. Report of the International Whaling Commission (Special Issue 13): 125-154.

Yoshida, H. and Kato, H. 1999. Phylogenetic relationships of Bryde's whales in the western North pacific and adjacent waters inferred from mitochondrial DNA sequences. Marine Mammal Science 15:1269-1286.

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