SealCam: Pinniped Paparazzi Shoot Fish

With a little help from a group of Weddell seals, a team of marine scientists has uncovered new information about the two ecologically most important fish species living far beneath the ice pack in the dark, frigid waters of Antarctica's McMurdo Sound.1 Behavioral ecologist Lee A. Fuiman of the University of Texas, Austin, biologists Randall W. Davis of Texas A&M University, Galveston, and Terrie M. Williams of the University of California, Santa Cruz, and their team at McMurdo equipped each of the pinnipeds with a sort of mini seal cam, then sent them down beneath the ice. "The objective of the research as it was initially planned and conceived was to study the Weddell seal," explains Fuiman. "We didn't expect to gather new information about fish species." This investigation actually emerged from data that these researchers and John Francis, of the National Geographic Society research and exploration committee, collected using mini-marine mammal cams over the course of three Antarctic summers in the late 1990s. The small packs—which feature a black-and-white video camera and data logger—are usually attached via a wet-suit-like belt and produce illumination through an array of near-infrared light emitting diodes (LEDs). (Infrared light is invisible to seals and fish, the researchers believe, and therefore does not interfere with normal behavior.) Lightweight and unobtrusive, the camera/data logger devices allow the researchers to videotape the mammal's movements and interactions with other species, taking the scientists to go on virtual journeys into oceanic worlds. Those virtual journeys returned a host of new data about those species' hunting habits, behavior, and deep-diving physiology.2,3 Garnering More Information than Expected After reviewing the tapes over time, however, Fuiman says, "we realized we had quite a lot of new information about the biology of the Antarctic silverfish [Pleuragramma antarcticum] and the Antarctic toothfish [Dissostichus mawsoni], two fish species that have been particularly difficult to study." They found that silverfish—a keystone species that essentially fills the ecological niche in the Antarctic that krill fills in the southern ocean—migrate from depths of 827 feet at night to 1,132 feet by day, guided by ambient light even during Antarctica's months of constant sunlight. "What's really intriguing is that these fish are definitely moving up and down with the clock, and seem to be moving up and down with light intensity, even though there's very little change in light intensity and that the light intensity is reduced by three meters of ice and two meters of snow on top of the water," points out Fuiman. The toothfish—"the major fish predator" with "the potential to control ecosystems from the top down"—has long been thought to be a deep-water species. "But our research shows that they're not as rare in shallower waters as we used to think," he adds. The revelations about the silverfish and toothfish species represent important new information, says Fuiman, especially considering previous knowledge was gleaned "from scientists who fished with bait and hook." Since the toothfish is also now a target of commercial fishing, the unique marine mammal cam technique for data collection may well become critical. "As a long-lived species that matures late, it would be very easy to [over fish and] endanger them," he explains. Fuiman, Davis, and Williams suggest that their marine mammal cams could be used to study a host of "other pelagic and deepwater fishes and invertebrates that are otherwise impossible to observe in their natural environment." They may be, in fact, on their way to doing just that. More to Come Although the researchers have uncovered as much new information as they can about the fish species from these videotapes, they recently returned from another three-month trip to Antarctica, where they had the Weddell seals record hundreds more hours of videotape. "We have barely reviewed the new tapes yet, but we have already seen a lot more fish, and that may lead to new data," Fuiman says. "In the first series of experiments, we ... drove the animals to our camp and a single ice hole; on this last trip we instrumented the seals and let them free range with all the other seals out there," Williams expounds. "It really was exciting. Some of them were diving straight down to the bottom and we saw things at 400 meters in the Antarctic ecosystem that no one has ever seen, because you can't send [remote-control diving vehicles] to these places. Invertebrates, starfish and things that look like they're from an entirely different planet were just whipping by these seals." Meanwhile, the original videotapes are still revealing "new physiological insights about the seals every day," says Williams, noting that another report on how the mammals' are expending and partitioning energy during the dives will be forthcoming soon. "While the videotapes have shown us what the seals are seeing, at the same time we have all this other instrumentation data that reveal speed, oxygen consumption, heart rate and so on, and we haven't even begun to match all those different physiological and performance variables. So, in addition to reviewing the latest videotapes, we are simultaneously still looking at all the other data from the first set of tapes." "We have so much videotape now," sighs Fuiman, "it's going to take years for us to go through it all." A.J.S. Rayl (ajsrayl@loop.com) is a contributing editor. References 1. L. Fuiman et al., "Behavior of midwater fishes under the Antarctic ice: observations by a predator," Marine Biology, March 2002, online at link.springer-ny.com/link/service/journals/00227/contents/01/00752/. 2. T.M. Williams et al., "Sink or Swim: strategies for cost-efficient diving by marine mammals," Science, 288:13-6, April 7, 2000. 3. A.J.S. Rayl, "Sink, swim ... or glide," The Scientist, 14[14]:1, July 10, 2000.

SealCam: Pinniped Paparazzi Shoot Fish

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