seal
Image: COURTESY OF LEE FUIMAN

To study the behavior of two elusive species of fish, scientists have enlisted the help of some unlikely photographers: seals. Antarctic silverfish and Antarctic toothfish, though abundant in the Southern Ocean, spend much of their time at great depths and under thick ice, making observation of these ecologically important creatures difficult. But as the fishes' natural predator, the Weddell seal knows exactly where to find them. Now, thanks in large part to data collected by seals equipped with video cameras, researchers have gained new insight into the fishes' mysterious ways. Their findings will appear in the March issue of Marine Biology.

Among other things, behavioral ecologist Lee Fuiman of the University of Texas at Austin and colleagues discovered that both species swim at shallower depths than previously thought. Whereas earlier data derived from trawling catches suggested that the anchovy-size Antarctic silverfish swim at depths below 400 meters, the seals found them between 160 and 414 meters down. Intriguingly, the fish moved up to shallower waters when the sun was lower in the sky. Whether this relates to the ambience of the light or to the dispersal of predators, however, remains to be seen. Similarly, the much larger Antarctic toothfish, thought to prefer depths of 300 meters or more, was spotted in waters as shallow as 12 meters.

To turn the seals into spies, the researchers attached video and data recorders to the heads and backs of the animals and then set them loose, hoping for the safe return of their equipment. Surrounded by near-infrared light-emitting diodes (LEDs), the video cameras could capture images to a distance of up to one meter in total darkness. Invisible to the seals and their prey, the emissions did not disrupt their normal behavior. This "seal cam" technique, the study authors note, could thus prove useful in future studies targeting other fish and invertebrates "that are otherwise impossible to observe in their natural environment."