AUSTIN, Texas—Enlisting the help of 15 Weddell seals as underwater photographers, researchers from The University of Texas at Austin have discovered important new information about two ecologically important fish species living far beneath the ice pack in the dark and frigid waters of Antarctica’s McMurdo Sound.
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Fuiman |
The research team discovered that silverfish (Pleuragramma antarcticum) migrate from depths of 827 feet at night to 1,132 feet by day. These movements coincide with changes in surface light intensity — even during Antarctica’s months of constant sunlight. Toothfish (Dissostichus mawsoni), previously thought to be a species living in deep water, frequently occurred at shallow depths, between 39 feet and 591 feet. The depth at which they swim may also change with the time of day.
Dr. Lee Fuiman, a behavioral ecologist with the university, said this is the first research project to employ marine mammals to photograph an entirely different animal species by carrying a combination video camera and data logger. Fuiman is a senior research scientist at the UT Austin Marine Science Institute in Port Aransas.
The research on the two fish species, the most important fish in the Antarctic in terms of abundance and crucial position in the food chain, is being published in the March issue of the journal Marine Biology, and currently is available online.
Co-authors include Dr. R.W. Davis of Texas A&M University Galveston and Dr. T.M. Williams of the University of California Santa Cruz. Fuiman, Davis and Williams previously have used seals, whales and dolphins as camera operators for research on their own species.
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Seals “observed” three different species of fish: a) Antarctic silverfish, b) Antarctic toothfish, and c) bald rockcod. Weddell seals frequently eat silverfish and rock cod and sometimes the much larger toothfish. Bald rock cod live just under the ice surface. Silverfish and toothfish inhabit much deeper and darker waters. |
“Few details are known of the habits of Antarctic midwater fish, especially those living below the heavy pack ice and shore-fast ice, because they are difficult to capture or observe at depth,” Fuiman said. “We used video sequences with synchronized positional data recorded by Weddell seals to describe such things as the location, movements, population trends and swimming behavior of the two fish species — popularly known as Antarctic silverfish and Antarctic toothfish.”
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(top) The head and pectoral fins of an Antarctic toothfish are silhouetted by the bright under-ice surface in shallow water (12 m deep).(bottom) As the seal approaches, the toothfish descends slowly using its large pectoral fins. Three vertical bands on the side of the fish become apparent. |
Previous knowledge of the habits of these two fish has been gained by trawling in ice-free areas, an inexact method at best, Fuiman said.
Fuiman said his team’s observations were made by attaching video cameras and synchronized multi-sensor data recorders to seals. Data was recorded as the marine predators foraged under the ice.
The researchers used black-and-white video and miniature, low-light sensitive video cameras encircled by an array of near-infrared light-emitting diodes (LEDs). Scientists believe that the infrared illumination from the LEDs was invisible to seals and fish and, thus, did not interfere with normal behavior. Yet, it enabled the camera to record images underwater in complete darkness to a distance of about one meter.
Ten male and five female seals made up the film crew. The sea mammal film crew members worked for four to five days at a time over three springtime field seasons at McMurdo Station. The research was supported by the National Science Foundation.
For more information, contact Dr. Lee Fuiman at (361) 749-6775 or (361) 749-6711 or e-mail <lee@utmsi.utexas.edu>. Also see Fuiman’s Web site and video clips.
