UH researchers test more sophisticated fish tracking.

You can radio tag a bird or a mammal to track their movements with GPS, but the technology doesn’t work so well under water.

Researchers have overcome this with satellite tags that report locations when whales or seals or turtles come to the surface. And there are tags that automatically release and float to the surface, where they can report their positions.

(Image: Map of fish tracking stations at Palmyra Atoll. Credit: UH Mānoa.)

But tracking a fish that stays down in the water can be a problem, so researchers have adopted sound waves as their tracking systems.

One solution has been acoustic monitoring, since sound travels well in the water. It works this way: you set up an array of precisely located listening devices on the reef. Then you attach small noisemakers to fish, and the sounds collected on the listening devices give you a sense of when fish are present and which microphone they’re closest to.

New research is fine-tuning the information.

“Previous methods were not formulated with the fish, ocean and acoustics in mind. They therefore do not exploit all available information, such as the biology of the fish limiting its range of possible movement.” Martin W. Pedersen, a UH Mānoa postdoctoral fellow.

Pedersen and Kevin C. Weng, manager of the Pelagic Fisheries Research Program at the University of Hawai‘i at Mānoa, published their new fish tracking model in the scientific journal Methods in Ecology and Evolution.

Pedersen and Weng’s new state-space model for estimating individual fish movement is two-part—one part that models the fish behavior, and one that models the detection of that behavior.

The system uses data on fish behavior, along with information on where fish are detected and where they are not detected to help pin down their precise locations.

“Knowing where the fish is not located actually tells you a lot about where it is located, and with our new method, we are able to utilize that information and achieve a better accuracy,” Pedersen said.

Their tracking model was tested in remote Palmyra Atoll, far to the south of Hawai`i, where 51 underwater observation stations were established. They were able to create maps that helped show where the fish were and how they moved.

“It helps us to better understand how they feed, breed and rest,” Weng said.  “Ultimately, more accurate movement information will help us to conserve these species.”

© Jan TenBruggencate 2013

Citation:  Pedersen, M. W., Weng, K. C. (2013), Estimating individual animal movement from observation networks. Methods in Ecology and Evolution. doi: 10.1111/2041-210X.12086