Jan. 21, 2002 By employing one underwater species to "spy" on two others through novel use of technology, Antarctic researchers have gained new insights into two little-known fish species. The team expanded their knowledge base by equipping Weddell seals to follow the fish and record their behavior.
The fieldwork by an eight-member team at McMurdo Station in Antarctica provides a rare glimpse into the habits of two very important Southern Ocean species, the Antarctic silverfish and the Antarctic toothfish, which is prized by commercial fishing fleets. It could also have wider applications in studying other species that thrive at great depths, the researchers argue.
The results of the work, supported by the National Science Foundation (NSF) were reported in the online version of the journal Marine Biology. The paper will appear in print in the March edition of the publication.
To obtain the images and data, Lee Fuiman of the University of Texas at Austin, Randall Davis of Texas A&M University, Galveston, and Terrie Williams of the University of California, Santa Cruz, equipped 15 Weddell seals over the course of three Antarctic summers with a video camera, infrared LED's and data recorders to track both their movements from their breathing holes through the water and their interactions with their prey.
"This use of a marine predator as a guided, high-speed sampling device for its midwater prey provided clarification and new insights into the behavior, interactions, and ecology of species that have been especially difficult to study," they write. "This new information expands the base of knowledge of two of the most important fish species in Antarctica and indicates that some existing notions about their distribution and behavior may need to be revised."
Much that is known about these key fish species comes from a variety of indirect evidence such as trawl catches, catches on hooks and from the stomach content of predators. But the camera and data recorders allowed these scientists to "accompany" the seal as surrogates on their hunts and to record firsthand what the seals and their prey were seeing and doing.
For the silverfish, this meant that the majority of the 336 fish were observed at depths greater than 160 meters (524 feet), with a few being watched at a depth of 414 meters (1358 feet). In the case of the toothfish, most encounters began at approximately 180 meters (590 feet).
The team's findings shed new light on the behaviors of the two species. For example, the researchers now believe, based on the "seal cam" data, that the silverfish migrate from deeper to shallower water using ambient light, even in the absence of a sunset during the Antarctic summer, as a cue.
"Nevertheless," they write, "our few observations of [silverfish] under the thicker permanent ice shelf suggest that light intensity may not be the only determinant of vertical position." More observation, they say, is needed to see if other factors, such as the distribution of predators or prey, which also may respond to the amount of ambient light, may also play a role in species distribution. The data also indicate that toothfish may be more common at depths less than 200 meters (656 feet) than previously thought.
Although their data were gathered in Antarctic waters and the researchers acknowledge that all data sampling techniques have their limitations, the "seal cam" technique, they argue, is promising and "could be used to study other pelagic and deepwater fishes and invertebrates that are otherwise impossible to observe in their natural environment."
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