Studies of Reproductive Strategies of Gray and Harbor Seals at Sable Island
Research
Research on Sable Island focuses on the lactation and mating strategies of gray and harbor seals. Seals spend most of their lives at sea, where they find an abundant supply of fish for food. However, they must come ashore to give birth and rear their young. This dichotomy has produced some of the most extreme mating strategies among mammals.
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| Hooded seals have the shortest known lactation period of any mammal, just four days. |
The current research on Sable Island is a collaboration between the National Zoo and Canadian Department of Fisheries and Oceans (DFO) scientists. In Canada, government-sponsored seal research focuses on the potential impact of seals on the commercial fisheries. In the U.S., however, all marine mammals are protected under the Marine Mammal Protection Act of 1972, and much of the research focuses on managing populations. Together, scientists study the basic ecological and life history processes of individual seals, while monitoring changes and effects on the populations as a whole.
To do this, the researchers employ state-of-the-art technologies, including:
- Radio transmitters – to locate and track seals
- Time-depth recorders – to measure length and depth of dives
- Satellite-linked time-depth recorders – to measure location and diving data
- Geographical Position System – to locate seals within three to five meters
- Isotope dilution techniques - to collect information on body condition and energy use
In addition to these, scientists use CritterCam and DNA analysis. Attached to a seal’s back, the CritterCam is programmed to videotape while the animal is at sea. Collaborator Greg Marshall of the National Geographic Society developed the CritterCam. Working with colleague Dr. Rob Fleischer, from the Molecular Genetics Laboratory, scientists assess levels of relatedness among seals using DNA analysis. This information is then used to answer questions about paternity and the effect of kinship on behavior.
The collaboration started in 1984 when the National Zoo's Dr. Daryl Boness and Olav Oftedal went to the ice pack off Labrador to study the lactation strategies of harp and hooded seals. Working with Dr. Don Bowen of DFO, on the Canadian research vessel Baffin and two helicopters, this early collaboration discovered the incredibly short lactation period of the hooded seal. Though a very successful expedition, cost and availability of resources, such as the Baffin, made any long-term program impossible.
The relationship struck up by the three researchers proved strong enough to overcome these obstacles, and long-term studies on Sable Island began in 1987. Previous work by the DFO resulted in a large number of tagged and identifiable animals with known ages, which in turn became the subjects of the current work on Sable Island.
