水中如何追踪鱼群

How do you track a fish? There's no "Google Maps" for finding fish. The radio signals that are the backbone of traditional GPS cannot pass through seawater. But sound travels remarkably well, so scientists often use acoustic telemetry（声波遥测） to estimate an individual fish's location. That means attaching an acoustic transmitter to a fish and then using a network of stationary underwater listening stations to monitor for the short clicking sounds that these tags emit. When a fish swims near to a receiver, its click is heard, and its individual code number is recorded.

Even with this clicker-listener observation network in place, though, there's much uncertainty about a fish's whereabouts at any given time. To date, most researchers have used ad hoc methods（特殊方法） to analyze their data, and typically have not quantified uncertainty.

"In science, knowing how certain or uncertain you are is often the prime objective," said Kevin C. Weng, manager of the Pelagic Fisheries Research Program at the University of Hawai'i at Mānoa and a graduate faculty member in the Department of Oceanography. "We're used to knowing within 20 feet where you can find that bison, wolf or bird. But underneath the ocean surface, we don't have the luxury of using GPS. So marine scientists use sound, which results in much lower accuracy."

But what is that accuracy? Martin W. Pedersen, a UH Mānoa postdoctoral fellow from Denmark, explains: "In the traditional tracking system, a fish is generally assigned the position of the receiver that detected it, even though the fish might be anywhere in that receiver's detection range. And if none of the receivers have heard from the fish for a while, no positions are assigned, even though the network may be providing some, albeit uncertain, information about the fish's whereabouts. For example, we could possibly estimate how far a fish could travel in a certain time since it was last heard, and could also infer locations where it isn't, due to the lack of detections."