National Geographic Today
By mounting video cameras on the heads of Weddell seals in Antarctic
seas, scientists have gained much insight into the life of the seals.
But the technique also provides another unexpected bounty: a rare
spy's-eye look at species the seals prey on.
Antarctic fishes, particularly those living in the freezing, dark waters beneath the ice pack, are difficult to capture or even observe. But during studies of the foraging behavior of Weddell seals, the researchers acquired considerable data on two important fish species: the Antarctic silverfish and the Antarctic toothfish.
The silverfish (Pleurogramma antarcticum) and toothfish (Dissostichus mawsoni) are major players in the ecology of the southern oceans, said fish biologist Lee Fuiman of the University of Texas at Austin. He led the study, which is published online in Marine Biology, at a research station in Antarctica's McMurdo Sound.
This far south in the High-Antarctic Zone there are no krill, Fuiman explained. So silverfish replace krill at the bottom of the food chain, providing a major source of food for fish, seals, whales, seabirds, and other creatures.
"The seals feed on these fish like popcorn, getting a hundred or so in a single dive," noted collaborator Terrie Williams of the University of California at Santa Cruz.
Silverfish are about 15 to 20 centimeters (six to eight inches) long. Trawling data has revealed that they are one of the most abundant fish in southern oceans, but little is known about where exactly they live.
Toothfish, which range from three to six feet (one to two meters) long, are both economically and ecologically important. Their similarity to the Chilean sea bassa popular menu item and a heavily overfished specieshas made them a recent target of the commercial fishing industry.
Fishing trawlers are heading farther south into the domain of the Antarctic toothfish, which, unlike the silverfish, is higher up on the food chain.
Video film from the seal-mounted cameras enabled Fuiman and his colleagues to get a much more detailed profile of where in the water column these fish spend most of their time, how fast they travel, and their vertical migrations during the day.
But the film, recorded over three years and captured by 15 seals, also revealed tantalizing details of the fishing techniques of the Weddell seals.
Weddell seals sunbathe during the Antarctic summer, hauling their huge blubbery bodies out of the frigid waters. Once the seals were on the ice, Fuiman and his colleagues lightly sedated them and took them to a lab, where the animals were rigged with a fist-size infrared camera; a computer that records depth, speed, and bearing; and satellite and radio tags.
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