Saildrones in the Arctic

In extreme circumstances, uncrewed systems help NOAA solve problems and fulfill its missions.

By Craig Collins

The writing had been on the wall for weeks, but it became official in May of 2020: Given the dangers and uncertainties posed by the global COVID-19 pandemic, NOAA Fisheries would have to cancel five of six planned research surveys in Alaska waters.

In a typical year, NOAA survey vessels collect detailed information about fish stocks through a combination of acoustic and trawl surveys: identifying schools of fish in the water column with sonar, and studying the biology and growth of fish scooped up in nets. These surveys are key data sources for managing critical fish stocks and establishing fishing quotas for species – including the Alaska pollock, the world’s largest sustainable fishery, accounting for about 5 percent of the entire global fish catch and valued at more than a billion dollars a year.

A saildrone rendezvous with the Coast Guard Cutter Healy (out of frame) in the Chukchi Sea in 2017.

NOAA’s reluctance to send dozens of crew members into the Bering Sea for a ship-based survey was understandable, given the risks, and Alex De Robertis, a fisheries biologist at NOAA’s Alaska Fisheries Science Center, developed a contingency plan for gathering at least some useful data on Alaska pollock. For several years he’d been experimenting with an uncrewed surface vehicle, the Saildrone, built by a company of the same name in Alameda, California, to perform long-range data collection missions in the ocean environment. De Robertis and colleagues from NOAA’s Pacific Marine Environmental Laboratory (PMEL), Kongsberg Maritime, and Saildrone installed a newly developed low-power acoustic sensor to the saildrone’s keel, and validated that it could provide accurate estimates in the Bering Sea by comparing saildrone measurements to those of research vessels.

Map of saildrone survey area.

Acoustic surveys work by sending sonar signals into water and measuring differences in density – essentially sensing the gas-filled swim bladders of fish. In another ocean environment, De Robertis explained, this method alone would not enable scientists to differentiate individual species – but in the Arctic, where species diversity is relatively low, that’s less of a problem. For 40 years, NOAA Fisheries scientists have been sampling midwater fishes via acoustic-trawl surveys of the Bering Sea, “And we know that our catches are more than 98 percent pollock by weight,” said De Robertis. “Alaska is a great playground for this technology because it is dominated by a single species. The measurements we are making would be very difficult to interpret in a useful way in high-diversity areas like a coral reef, where you would encounter many species.”

Planned saildrone survey transects. The colors indicate the tracks of different saildrones.

The saildrone is a remotely operated surface vehicle, about 23 feet long, propelled by wind acting on a 15-foot-tall rigid sail. Its sensors and other equipment are powered by solar cells. It can take weather, temperature, current, and biochemical readings from air and water. “Once they’re launched, it does not take much to keep them going,” De Robertis said. “They don’t run out of fuel – they run on sunlight and wind – so they can last for a really long time. And they are very efficient.” Saildrones, like all oceangoing vessels, need an occasional cleanup, after parts are fouled by debris and living organisms, but they can operate for months, traveling a programmed route that can be adjusted or changed by remote operators.

De Robertis, anticipating the cancellation of the Alaska fisheries surveys, began discussions with colleagues at NOAA Fisheries and Saildrone in March to see if the systems could help gather data on the pollock fishery. PMEL joined the project, to make oceanographic and meteorological data available for weather prediction in the Bering Sea region. A little more than a week after signing a contract with NOAA, Saildrone launched three vehicles from its headquarters on Alameda Island in mid-May. About six weeks later, in early July, the saildrones completed their 2,000-mile transit to the Bering Sea and began sounding for pollock.

While the unmanned survey will offer useful data to fisheries managers in 2020, De Robertis cautions that this does not replace the capabilities of a shipboard crew of fisheries scientists. Trawl samples allow for a fuller picture of a fish population. “We can definitively tell their species, size, and age from trawl samples,” said De Robertis. “And we can make physiological measurements, much like the tests you get at a doctor’s office, to understand how the fish are doing.” No sensors can replace that capability, but De Robertis sees a future in which uncrewed surface vessels can complement these seasonal surveys – particularly in the high Arctic, where accessibility is limited and there are, as yet, no ports deep enough to accommodate NOAA survey vessels.