In the bestiary of bizarre ocean creatures, there are few animals stranger than the jawless, finless sea lamprey. These eel-like fish are parasites, latching on to larger fish and boring into their skin with a tooth-lined sucker to feed on the blood of their prey.
Sea lampreys are among an elite collection of anadromous fish—saltwater fish that spawn in freshwater—a trait they share with much more palatable species like salmon, striped bass, and sturgeon. As the Great Lakes became increasingly channelized in the mid-19th century to permit shipping from the Midwest to the Atlantic coast, sea lampreys, native to inland lakes in New York and Vermont, invaded. Over the next century, they would decimate native fish populations in Lake Huron, Lake Michigan, and Lake Superior.
They are relentless invaders, and tracking their spread has proven to be an exercise in futility, at least for human observers. But a new robotic challenger has emerged.
GRACE (short for Gliding Robot Ace) is as unusual among underwater robots as sea lampreys are among freshwater fishes. Eschewing the conventional thrusters or ruddered propellers of most underwater robots, GRACE instead packs a powerful tail fin to propel it forward. This is supplemented by a glider system: By changing its buoyancy, GRACE can propel itself forward by ascending and descending through the water column. This is an exceptionally efficient configuration, giving GRACE an enviable multi-week endurance while patrolling for lampreys around Lake Michigan.
Grace 2.0 out for testing in August.
GRACE is the brainchild of Dr. Xiaobo Tan of Michigan State University, and he's thinking seriously about developing a powerful, multi-user platform. "We're not just trying to publish a paper," said Dr. Tan, "we want to make something really functional." GRACE's tracking system is built on a standardized acoustic monitoring protocol that is used throughout the Great Lakes, as well as many other marine and freshwater systems to track everything from salmon to bull sharks.
Here's how it works: Researchers capture fish of interest and tag them with an acoustic pinger. The pinger responds to signals from a transducer, which provides a rough estimate of location. Add a second transducer and researchers can triangulate the fish's location.
This type of system allows researchers to track the movement of tagged fishes as they travel into and out of the lake, and can reveal spawning aggregations, nursery grounds, and population centers. But there are major limitations: the transducers are either static, which limits the range a fish can be tracked; or mounted on a boat, which requires people to continuously monitor the system, limiting the amount of time a fish can be tracked.
An autonomous robotic fish, swimming through the lake, constantly monitoring tagged animals, overcomes both those limitations.
Dr. Tan's ultimate vision is a swarm of GRACE robots, continuously swimming across Lake Michigan, communicating with each other, and triangulating the location of tagged sea lampreys or other species of interest. It's an incredibly adaptable mobile platform, one that can support a variety of Great Lakes monitoring programs.
GRACE supplements the Great Lakes Acoustic Telemetry Observation Systems (GLATOS), a collaborative network of researchers who use acoustic telemetry to monitor fish in the Great Lakes. But GRACE's mobility is the killer application that makes this platform a compelling addition to GLATOS, as GRACE can cover a much greater area than GLATOS, and move with the fish it's tracking. Following schools of fish is where its design really shines. Rather than noisy propellers, which can become mired in seagrass and potentially injure wildlife, GRACE moves more naturally through the lake.
"[The design] minimizes impact on the environment." said Dr. Tan. "We don't want a noisy machine."
Building a new kind of underwater robot is not without its challenges. Every new component comes with its own host of difficulties. GRACE, now in its second generation, is the product of intensive testing and evolution.
"We fail, we try again," said Dr. Tan. "The biggest hurdle is system integration—how to integrate all mechanical, electrical, and software elements and make sure the robot works reliably in real-world environment."
Even these prototypes will enter common use for Great Lakes researchers. Though Dr. Tan doesn't foresee full implementation of his vision until at least the third generation of GRACE prototypes, earlier units are shared with the research community, to support other acoustic monitoring programs.
GRACE is backed by the Great Lakes Fishery Commission, the National Science Foundation, and the US Geological Survey. Dr. Tan plans to continue adapting and refining its systems, and predicts at least another two years to realize his vision for GRACE. In an ocean of autonomous underwater robots that are often more hype than function, GRACE stands out as one of the few systems driven by proven prototypes over press releases.