Fish are more than just food or friends for scientists, as marine critters become the focus of a new U.S. military program called Persistent Aquatic Living Sensors or PALS.

Marine creatures can naturally navigate the ocean freely and sense objects and movement underwater effortlessly. Humans are far more limited beneath the ocean's surface.

In a bid to monitor and keep track of increasing activity in the oceans, the U.S. military is recruiting fishes and other marine creatures as "spies."

Fish Are DARPA's New Partners

According to a group of researchers from the Defense Advanced Research Projects Agency (DARPA), marine creatures can be the effective and cost-efficient key in improving the Department of Defense's monitoring capabilities.

"The PALS program was developed to leverage the great sensitivity that organisms have in the ocean to changes in their environment," Lori Adornato, manager of the PALS initiative, says in Scientific American.

Since marine organisms are naturally equipped to sense and respond to even the most minute disturbances in the ocean, researchers can simply tune in to their behavior and detect underwater vehicles. Changes in the movements, light emissions, and sounds of marine animals can be tell-tale signs of a shift in their environments.

For example, schools of fish are known to change their swim patterns when they're under attack or there are foreign objects present, according to Discover Magazine. By observing certain species, DARPA can learn to read their movement and swim patters, so they know how it changes when an interloper or unauthorized vehicle is nearby.

Bioluminescent organisms can also be observed, since they signal changes in their environment with their light patterns.

Snapping shrimps offer a particularly promising possibility, since these animals are plentiful in reefs and they make very loud sounds that hydrophones can easily detect.

"The idea is that the sounds that the shrimp create would travel to the object, reflect off of it and we would be able to detect it at our sensors," scientist Alison Laferriere of defense company Raytheon BBN explains to Discover Magazine.

Laferriere is conducting research in hopes of developing methods of using shrimp as a natural sonar.

A Promising Cost-Effective Surveillance Option

With plenty of underwater drones in development by various countries, some of which even carry nuclear weapons, being able to "hear" these vehicles is a huge advantage for the U.S. military.

Scientific American reports that five research teams have already been granted a total of $45 million by DARPA to study and observe various marine organisms and their behavior toward underwater vehicles.

Not only is the PALS methods believed to be effective and efficient, but scientists say they're expected to be more discreet and affordable options.

Sonar sensors are effective, but they're expensive, labor-intensive, and often limited in scope. Living marine organisms do not need external power and offer a much wider scope.

Of course, relying on living creatures does have its drawbacks, including the need to install detectors to observe the animals. Installation could face the same cost and technological limitations as solar sensors in the end.

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