Over the last two centuries humans have killed hundreds of thousands of sperm whales. Much to our surprise, we understand very little of these creatures and much of what we "know" turns out to be myth, as revealed by our recent genetic studies. For example, examination of stranded groups of whales in Tasmania revealed that these groups are not strictly matrilineal, as previously believed, but instead contain many unrelated individuals. Sperm whales remain one of the most mysterious of the great whales because they live in remote deep waters; so far these animals have defied most attempts to attach satellite tags, which would help us to understand long-term and long-distance movements. Thus, genetics are among the only tools that may unlock the secrets of these denizens of the deep.
Killer whales attacking sperm whales off the California coast (H. Neville)
Sperm whales are extreme creatures in many ways. They are the largest of the toothed whales and they have one of the most extensive global distributions of any marine mammal species, rivaled perhaps only by the killer whale (Orcinus orca). They are found in all deep (>1000m) oceans of the world from the equator to the edge of the pack ice. Sperm whales are the most sexually dimorphic of the cetaceans, with mature males reaching 18m in length and females 12m. Sperm whales prey mainly upon meso- and bathypelagic squids and fishes. When foraging, they are typically submerged to about 400-600m for 40 minutes, followed by 10 minutes at the surface. However dives to 2500m and possibly 3200m have been noted, as well as dives lasting as long as 138 min. They have the largest brain on earth and are remarkable for their strong social bonds.
When populations are comprised of groups that contain related individuals, traditional methods of estimating population structure are biased; our work provides a new look at sperm whale stock identity in the North Pacific by taking into account the social structure of the species. This is a molecular project in which we use both nuclear and mitochondrial markers to determine population and social structure and in which we design new analytical techniques to remove the bias due to relatedness. We have looked at hundreds of individuals across the North Pacific within dozens of social groups. Currently, NOAA Fisheries manages three stocks of sperm whales in the North Pacific: the California/Oregon/Washington, Hawaii and Alaska stocks. Our goal is to re-examine these stock designations using molecular genetic data. In addition, we use the genetic data to determine patterns of relatedness within groups of sperm whales encountered at sea. These data shed light on the evolution of sociality at sea and the nature of social bonds in groups of free-ranging cetaceans.
Biopsy of sperm whales in the eastern tropical Pacific (Marine Mammal and Turtle Division, SWFSC, Fearnbach and Douglas)
We also work in collaboration on a number of different management issues involving sperm whales. We are involved in a project on sperm whales that have learned to eat fish caught on longlines in the Gulf of Alaska (with Jan Straley, University of Alaska). To aid mitigation efforts, our work provides information from genetic markers to identify the gender, number of individuals and population identity of the animals involved. A collaborative effort with Phillip Morin and Terry Gasterlaand (Scripps Institution of Oceanography) uses sperm whales as a model system with which to develop single nucleotide polymorphisms (SNP) markers for use in conservation genetics. Another project we are pursuing involves combining data from a group of international researchers (Hal Whitehead, Dan Englehaut, Kenneth Richard, Mary Dillon, and Jo Bond) to examine worldwide population structure in sperm whales based on mitochondrial markers. We are also interested in the use of acoustic signals to discriminate stock boundaries and how analyses using acoustic data compare with those using molecular data (with Hal Whitehead, Dalhousie University, and with John Hildebrand, Scripps Institution of Oceanography).
Adult male sperm whale following a sablefish longliner (Marine Mammal and Turtle Division, SWFSC)
Mesnick, S.L., Evans, K. Taylor, B.L., Hyde, J., Escorza-Trevino, S and Dizon, A.E. 2003. Sperm Whale Social Structure: Why it Takes a Village to Raise a Child. Pages 170-174, In, Animal Social Complexity: Intelligence, Culture and Individualized Societies (F.B.M. de Waal and P.L. Tyack, eds.). Harvard University Press.
Mesnick, S.L. 2001. Genetic Relatedness in Sperm Whales: Evidence and Cultural Implications. Behavior and Brain Science 24(2):346-347.
Mesnick, S. L., Taylor, B.L., Le Duc, R.G., Escorza Trevino, S., O'Corry-Crowe, G.M. and Dizon, A.E. 1999. Culture and Genetic Evolution in Whales. Science, 284: 2055a
Mitchell, E. A., Mesnick, S.L. and Allen, A.C. 2002. Sperm Whale Depredation in the Demersal Longline Fishery for Sablefish, Anaplopoma fimbria, in the Gulf of Alaska: Research Needs and Approaches to Mitigation. Working Paper for the Workshop on Cetacean Interactions with Commercial Longline Fisheries in the South Pacific Region: Approaches to Mitigation, Apia, Samoa, November 2002.
Pitman, R.L., Ballance, L.T., Mesnick, S.L. and Chivers, S. 2001. Killer Whale Predation on Sperm Whales: Observations and Implications for Large Whale Biology. Marine Mammal Science: 17(3):494-507.
Ruiz Castro, R. I., Gendron, D., Agu i n iga, Mesnick, S.L. and Carriquiry, J.D. 2004. Trophic relationships between sperm whales and jumbo squid using stable isotopes of C and N. Marine Ecology Progress Series. 277:275-283.
Taylor, B.L. and Mesnick, S.L. Manuscript. In prep. Kin-Be-Gone: a program for removing related individuals from data sets when estimating population structure. Submission to Molecular Ecology.
Whitehead, H. and Mesnick, S.L. 2003. Social structure and effects of differential removals by sex in sperm whales: methodology. Working paper SC/55/O18 at the 55th Annual Meeting of the International Whaling Commission. Berlin, June 2003.
Whitehead, H. and Mesnick, S.L. 2003. Population structure and movements: genetic, acoustics and marks. Working paper SC/55/O14 at the 55th Annual Meeting of the International Whaling Commission. Berlin, June 2003.