The US military wants to enlist fish and other sea life to help it track enemy submarines at sea. The Persistent Aquatic Living Sensors program could also modify existing species to make them better underwater spies, an effort that would face stiff opposition from environmental groups.

The Defense Advanced Research Projects Agency, the Pentagon’s blue-sky research and development wing, announced the PALS earlier this month. The program "will study natural and modified organisms to determine which ones could best support sensor systems that detect the movement of manned and unmanned underwater vehicles," DARPA stated on its website.

The idea is that marine life—everything from bacteria to plankton and corals to fish and mammals—senses and in some way reacts to the presence of nearby ships. To DARPA, those reactions represent valuable data. "The program simply plans to observe the natural, unique behaviors of marine organisms in the presence of targets of interest, and to process those data to provide an alert," Jared Adams, a DARPA spokesperson, told me via email.

If the military can develop a system for detecting ocean life's reactions to passing vessels, it could in theory monitor all the world's oceans for enemy activity—and do so more cheaply and effectively than with purely manmade sensors. "Beyond sheer ubiquity, sensor systems built around living organisms would offer a number of advantages over hardware alone," DARPA stated.

For one, sea life "self-replicates and self-sustains"—that is, breeds—so the military wouldn't have to maintain hardware that breaks down, rusts, and runs out of power. Moreover, sea life senses its environment in a number of different ways, potentially giving military analysts a more comprehensive view of the oceans.

"Evolution has given marine organisms the ability to sense stimuli across domains—tactile, electrical, acoustic, magnetic, chemical and optical," DARPA explained. "Even extreme low light is not an obstacle to organisms that have evolved to hunt and evade in the dark."

PALS concept art. ImageL DARPA

We don’t know how exactly PALS would work in practice. Right now, DARPA considers the program to be a "fundamental research program," Adams said. Military scientists would have to figure out how to record, on a massive scale and at great distances, animals' reactions to nearby ships. They would need to write computer code to process raw data from two-thirds of Earth's surface into useable intelligence.

And there's another obstacle: the objections of people and organizations opposed to the militarization of sea-dwelling creatures. "It is bad enough that the military regularly conducts exercises that impact large numbers of whales and dolphins, but now they want to actually involve marine mammals in their plans rather than just making them the victims," John Hocevar, Greenpeace USA's oceans campaigner, told me via email.

Adams said that DARPA would not include endangered species and "intelligent mammals" in the PALS program, but it's not clear how the agency defines "intelligent." The US Navy already uses trained dolphins and sea lions to find underwater mines and other objects. Nor has DARPA explained how it proposes to separate data provided by, say, an endangered tuna species from similar input from tuna species that aren't endangered.

Equally worrying, DARPA proposes to modify some species in order to optimize their senses for detecting manmade objects. The resulting breeds would essentially be genetically-modified organisms and could disrupt or even collapse existing ecosystems.

Adams said DARPA would create and test modified species strictly in "contained, biosecure facilities." But to actually deploy modified species, the military would have to release them into the wild, where they could drive out, outeat, or outbreed unmodified species.

For Sea Shepherd, a Washington State-based ocean conservation group, the problem with PALS is moral rather than practical. Possible harm to marine life is "beside the point," spokesperson Heather Stimmler told me via email. "We believe marine mammals should be left alone in the ocean where they belong to live their lives as nature intended, not 'used' by anyone for any reason."

For now, DARPA is moving forward with its effort to enlist sea life. The agency has announced a meeting in Virginia on March 2 for interested researchers.