In 2020, the developing COVID-19 pandemic led to the cancellation of fisheries surveys worldwide. This posed a challenge for fisheries management, which relies on timely and consistent abundance estimates of fish stocks to support management decisions.
The latest Editor's Choice article, “Uncrewed surface vehicle (USV) survey of walleye pollock, Gadus chalcogrammus, in response to the cancellation of ship-based surveys", describes an effort to fill this information gap. USVs equipped with sonar instruments were used to conduct an acoustic survey of walleye pollock in Alaska's eastern Bering Sea. The authors developed contingency plans for a USV-based survey in spring 2020 in case the planned summer ship-based surveys were cancelled. The goal was to generate an abundance index consistent with the conventional ship-based acoustic-trawl survey in time to provide management advice. The summer ship-based surveys were cancelled due to safety concerns and ultimately, this USV survey became the only source of fishery-independent information in 2020 for this important fishery.
Three chartered saildrone USVs were used to conduct a survey of pollock abundance. The robotic sailboats left California in mid-May, and sailed 2,200 nautical miles to the Bering Sea. Each surveyed a third of the area typically covered by the ship-based survey and returned to California in October after nearly five months at sea.
In conventional ship-based acoustic-trawl surveys, trawl catches are used to establish species and size compositions of acoustically detected fish aggregations. These catch data are then used to convert the acoustic signals into estimates of fish abundance. The USV survey lacked such sampling of species and size composition, which remains a major challenge for USV-based acoustic surveys. However, in the Bering Sea, pollock consistently dominate acoustic signals from fish aggregations. Re-analysis of previous surveys established that in this low-diversity ecosystem, robust relationships could be derived to convert the USV acoustic observations into an estimate of total pollock biomass. The results of the USV survey were incorporated into the stock assessment and informed management advice in a situation when ship-based surveys were not possible.
USVs are becoming increasingly accessible. Efforts in this area are rapidly transitioning from technology development to investigations of how to best use these new platforms to understand the abundance, behavior, and distribution of marine organisms. This work demonstrates that USVs have the potential to inform fisheries management in low-diversity ecosystems.
Uncrewed survey vehicle (USV) departing for the survey (left); tracks of the three USVs (right).