Home


       

Genetic Diversity of Central Pacific Marine Mammals

Recent studies of genetic diversity in marine mammals have investigated patterns of paternity and kinship, the effects of near-extinctions on reductions of genetic variability, migration patterns of populations, and the differentiation of populations applicable to the management of stocks (Hoelzel 1993,1994). To date, paternity and kinship patterns have not been investigated in western Pacific Island marine mammal populations (Hoelzel 1994). Reductions of genetic variability were created by the near-extinctions in the late 19th and early 20th century of the Hawaiian monk seal (Figure), North Pacific right whale, and northern elephant seal, creating historical genetic bottlenecks for these species (Hoelzel 1993; National Oceanic and Atmospheric Administration 1996). Genetic investigation of cetacean migration patterns in the North Pacific established that humpback whales from the western and Hawaiian breeding populations disperse to several discrete feeding grounds around the Pacific (Baker et al. 1993). In contrast, minke whales from distinct breeding populations mingle in common feeding areas (Hoelzel 1994).



Figure. A female Hawaiian monk seal with her 4-week old pup at Laysan Island, northwest Hawaiian Islands. Courtesy B. Becker, National Marine Fisheries Service

Most investigations of genetic diversity in western Pacific cetaceans have concentrated on identifying the degree of divergence of geographic or morphological populations. Divergent genetic populations are considered stocks that can be used to evaluate the status and trends of these species (Dizon et al. 1992). Less is known about this differentiation in the western Pacific than in most other areas. For example, no information exists on genetic variability of 12 species of small cetaceans found in the U.S. Pacific Islands. Even the species identity of the tropical bottlenose whale is unknown (Jefferson et al. 1993).

   

Genetic investigations have clarified the status of controversial cetacean populations. Genetic divergence of minke whale populations in the North Atlantic, North Pacific, and Antarctic is as great as that found between other whale species, suggesting that these populations deserve recognition as at least subspecies (Wada and Numachi 1991; Dizon et al. 1992). The Bryde's whale, which may be the most common great whale of the tropical Pacific Islands, is differentiated into a larger offshore form and smaller inshore form (Wada and Numachi 1991). Studies of mitochondrial DNA suggest that the large form is a distinct species. Morphologically distinct short- and long-nosed forms of the common dolphin also show a high level of genetic distinctiveness (Rosel et al. 1994).

   

Many of the smaller cetaceans found near U.S. Pacific Islands have more complex population structures. Killer whales are highly mobile with little morphological variability. Although their stock structure is not well understood, their social behavior and preliminary genetic data suggest considerable genetic variability among pods in a single region (Hoelzel 1993,1994). In contrast, eastern Pacific spinner dolphins have morphologically distinctive forms that are not genetically divergent, compared to a population in the far western Indo-Pacific (Dizon et al. 1991). Genetic intergradation and a zone of hybridization in eastern Pacific spinner dolphin stocks have been suggested as causes of this morphological differentiation, in the absence of genetic divergence (Dizon et al. 1991, 1994).

   
  Author
Bruce C. Mundy
National Marine Fisheries Service
National Oceanic and Atmospheric Administration
Honolulu Laboratory
2570 Dole Street
Honolulu, Hawaii 96822

References


Home