Please select your home edition
Edition
Maritimo 2023 M600 LEADERBOARD

Scientists use uncrewed surface vehicle to estimate krill abundance in Alaska

by NOAA Fisheries 22 Feb 16:58 UTC
Krill (Thysanoessa inermis) © NOAA Fisheries

Throughout the world, scientists engage in regular vessel surveys to produce estimates of species distribution and abundance. These estimates let scientists track species- and ecosystem-level trends over time to support ecosystem-based fishery management.

Increasingly, scientists are exploring ways to conduct these important surveys more efficiently without jeopardizing the quality of the data they have collected consistently.

In a new study, NOAA Fisheries scientists filled a data gap by combining observations from uncrewed surface vehicles and a commonly used machine-learning algorithm. As a result, they were able to estimate krill abundance in 2020 when a standard vessel survey was not possible.

In the eastern Bering Sea, scientists conduct biennial acoustic-trawl surveys from the NOAA Ship Oscar Dyson, a crewed vessel. The primary goal of these surveys is to estimate walleye pollock abundance and distribution. This commercially valuable fishery is the largest volume fishery in the United States. However, the acoustic-trawl surveys have also provided estimates of krill abundance extending back to 2004.

Krill are a major component of the eastern Bering Sea ecosystem, providing an important food source for fish, seabirds, and marine mammals. Thus, krill abundance is an important indicator of ecosystem status and prey availability. In 2020, the Covid pandemic forced the cancellation of the eastern Bering Sea acoustic-trawl survey.

A combination of technological approaches supports long-term science

As a partial replacement for the lost survey effort in 2020, scientists used three saildrones to collect acoustic data. They still were able to estimate pollock abundance and distribution despite the survey cancellation. In this study, these same data also were used to estimate krill abundance and distribution.

"The big challenge we faced using uncrewed surface vehicles to estimate krill abundance was that we had less informative acoustic data available than we did from our NOAA research vessel," said Mike Levine, lead author of the study and fisheries biologist at the Alaska Fisheries Science Center. "The sonar instruments these uncrewed systems carried had to be more compact and only provided acoustic data at two frequencies. This contrasts with the standard vessel-based survey, which provides four-frequency acoustic data for krill estimates."

Scientists faced a challenge. Four frequencies have traditionally been used in this survey to identify krill. Applying the standard processing algorithm with two frequencies instead of four produced an estimate that was much more uncertain and overestimated krill abundance.

The solution was to apply a simple machine learning approach known as a random forest algorithm. Scientists trained the model to identify krill with only two frequencies using data from previous crewed surveys. They checked the model performance by running the method on previous surveys not included in the training data, then compared the results to the standard four-frequency result.

The random forest approach worked. It produced a comparable estimate to the standard survey for the year of missing data. Scientists were able to keep the time series going despite the lack of a ship-based survey in 2020. Still, the results of the two-frequency random forest approach are more uncertain than those based on four frequencies. Additionally, there is a loss of trawl sampling for krill, which allows scientists to collect other important biological information (e.g., species and size).

"In many situations, the loss of trawl sampling is a major limitation in the use of uncrewed vehicles in place of ship-based abundance surveys. The uncrewed surface vehicle approach worked well to 'fill in' 1 year of missing krill survey data in this case because we use a multi-year average of size and species composition to estimate krill in the eastern Bering Sea," said Alex De Robertis, coauthor and fisheries biologist from Alaska Fisheries Science Center. "However, we really need to be able to do direct sampling or we could miss long-term changes in krill size, species composition, or range. Thus, continued trawl validation of acoustic data is prudent."

Large-scale surveys can be disrupted for any number of reasons—such as mechanical breakdown, instrument failure, and even unexpected events like a global pandemic. Uncrewed surface vehicles provide a pragmatic way to address some of the challenges faced in continuing long-term survey time series. However, uncrewed surface vehicles may provide scientists with less or different information than survey vessels. This study provides an example of how machine learning can be used to maximize the information derived from these data sources.

Scientists found that the random forest approach can be a simple, straightforward method to implement, and an effective tool to address changes in survey methods or data.

Related Articles

Oregon Coast coho sustain sportfishing seasons
Rebound of wild populations boosts productivity enough for harvest Low salmon returns have closed salmon fishing in California and limited it elsewhere on the West Coast. But Oregon anglers have enjoyed robust sportfishing on a strong wild salmon species. Posted on 23 Dec 2024
Some fish and crab may shift further north
New regional models are being developed for the Bering Sea to better anticipate climate change The eastern Bering Sea is a highly productive marine ecosystem, supporting more than 40 percent of the annual commercial fisheries landings by volume in the United States. Posted on 21 Dec 2024
How the 2024 hurricane season impacted fishing
Learn how business owners, marine ecosystems, and recreational fishing seasons were affected The 2024 Atlantic hurricane season, which officially ended on November 30, showcased above-average activity. It had a profound impact on recreational fishing in the Gulf of Mexico, causing recreational fishers to face challenges and interim closures. Posted on 20 Dec 2024
Climate, Ecosystems, and Fisheries
Climate change is impacting the nation's valuable marine and Great Lakes ecosystems The NOAA Climate, Ecosystems, and Fisheries Initiative (CEFI) is an effort to provide decision-makers with the information they need to prepare for and adapt to changing oceans and climate. Posted on 7 Dec 2024
Fifteen years of searching for smalltooth sawfish
NOAA Fisheries scientists have been studying smalltooth sawfish in South Florida since 2009 NOAA Fisheries scientists have traveled to South Florida multiple times a year for 15 years to study smalltooth sawfish. Posted on 17 Nov 2024
Harbor Seals consume up to a third of Steelhead
Unchecked predation may undermine recovery actions, study finds Harbor seals consume as many as a third of young steelhead smolts migrating out of the Nisqually River's delta in southern Puget Sound, new research shows. Posted on 21 Sep 2024
The Elwha River restoration
Elwha River restoration project offers valuable insights into the complex ecological processes Elwha River restoration project offers valuable insights into the complex ecological processes involved in dam removal and river recovery. Posted on 16 Sep 2024
Reestablishing connections for fish and tribes
North Santiam River is a high priority for the recovery of Upper Willamette River spring Chinook With $710,000 in funding from NOAA, the Confederated Tribes of the Grand Ronde will remove barriers to the passage of threatened salmon and trout species on their land. Posted on 16 Aug 2024
Progress update on two fishing data initiatives
Fishing Effort Survey study and the collaborative initiative to re-envision the partnership We may be in the dog days of summer, but I am pleased to share that progress continues on two high-visibility recreational fishing data collection initiatives — Fishing Effort Survey study and the collaborative initiative to re-envision the partnership. Posted on 15 Aug 2024
Teams and technology trace Klamath River recovery
By tracking new salmon returns The removal of four dams on the Klamath River will reopen more habitat to Pacific salmon than all previous dam removals in the West combined. Posted on 10 Aug 2024
Maritimo 2023 M600 FOOTER