What top predators can tell us about ocean ecosystems
Dr. Sara Iverson, scientific director of the Ocean Tracking Network Canada and a University Research Professor at Dalhousie, along with
graduate student Gregory Thiemann and Ian Stirling from the Canadian Wildlife Service, examined the diets of 1,700 polar bears across the Canadian Arctic over a 30-year period using the “quantitative fatty acid signature analysis” (or QFASA for short) she developed. QFASA has proven to be an important tool, allowing researchers to do their work without harm to the animals. Prior to its development, estimates of diet were imprecise and limited to only the animal’s last meal.
From a sample of animal fat, Sara Iverson can determine what predators at the top of the food chain are eating, and by extension, how their diet has changed due to changes in ecosystem.
QFASA is one of several innovative tools researchers have to study marine mammals, which are elusive subjects because they spend so much of their time in the sea. Others include satellite tags, physiological and chemical tracers and “critter cams,” which let the researchers “see what the seal sees.
The polar bear is the first animal to be considered vulnerable because of the consequences of climate change. (Polar bears are listed as a threatened species under the Endangered Species Act in the U.S. and as a “species of special concern” in Canada.)
It can still be quite a process to obtain the samples required for analyses. For example, the male northern fur seal is notoriously vicious, given its massive size (340 kg) and predilection for fighting.
To study fur seals, the researchers (three at a time) assemble in a plywood box with no ceiling or floor, and shuffle into the midst of the rookery. They bring females into the box one at a time, take samples and attach a tag, before releasing them again, all the while with one person on the lookout for the ornery male.
“Polar bears are absolutely dependent on sea ice to hunt seals, which use the ice as a platform to breed. With the loss of ice, they’re having a difficult time. A major source of food has been removed and in some areas they’ve been forced ashore earlier in the spring in poor condition.” -Dr. Sara Iverson, scientific director of the Ocean Tracking Network Canada and a University Research Professor at Dalhousie.
“You have to have a good sense of humor and there are times when you think, ‘what in the world am I doing here? But it is absolutely incredible to see these animals in their natural environment.” -Dr. Sara Iverson, scientific director of the Ocean Tracking Network Canada and a University Research Professor at Dalhousie.
“You go to spectacular places and work with amazing animals. Sometimes I can’t believe they actually pay me to do this. You cannot be handed the data and have the same feel for it. Field work give you an insight you would not get otherwise.” -Dr. Sara Iverson, scientific director of the Ocean Tracking Network Canada and a University Research Professor at Dalhousie.
|Sara Iverson |
Dr. Iverson and other researchers enter the northern fur seal rookery in a plywood box
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