How is ocean acidification information used by fisheries managers?
Each year, information collected by over 100 scientists across Alaska and beyond is gathered and synthesized into an Ecosystem Status Report (ESR) for the North Pacific Fishery Management Council (NPFMC). The NPFMC is responsible for managing federal fisheries in Alaska, and the annual reports are produced for each ocean basin and help fisheries managers track indicators important to fish populations.
Starting in 2019, a section on ocean acidification began appearing in the “emerging issues” section of the report for the Bering Sea. These sections have helped managers begin to learn about and factor in ocean acidification over time. An ocean acidification section was also included in the Gulf of Alaska report in 2023 and will likely appear every other year. This article will cover the Bering Sea and a future article will look at the Gulf.
Bering Sea Crab Vessel. Photo credit by NOAA.
What elements of ocean acidification are the focus for the Bering Sea?
Scientists at the University of Washington and NOAA are generating model-based ocean acidification forecasts and hindcasts to help us understand current conditions and track change. These efforts focus on summer bottom waters because this is where the most acidic conditions are expected to develop (due to the combination of ocean acidification and natural seasonal biological respiration.) Summer is also when temperatures are close to their highest and are thus most likely to have synergistic negative effects on crab.
The information presented in the ESR includes spatial plots showing the current summer’s bottom water conditions, and the anomaly after removing the slow, consistent ocean acidification trend. Removing this trend highlights the role of natural processes, which generate most of the year-to-year variability in the carbon system. An index is also presented showing the percent of total shelf bottom waters which are below thresholds that could impact species. This includes pH values ≤ 7.8 which negatively affects growth and survival of red king and tanner crab, and Ωarag < 1 which negatively affects bivalve larvae. The goal of the map and index are to provide a quick assessment of the summer water pH and Ωarag conditions compared to previous years. Developing these model products is an iterative process and researchers are continually working on improving model performance through comparisons with data collected in the Bering Sea.
Primary Findings for 2024
- Modeled bottom water pH and Ωarag both increased compared to the relatively low values in 2023. This means the water was slightly less acidic/corrosive than the previous year.
- Overall, bottom pH and Ωarag values are still low (i.e. more acidic/corrosive) relative to the entire model timeframe. This is driven mainly by the long-term decreasing trend caused by ocean acidification.
- The research team anticipates that natural variability will continue to be the dominant source of interannual variability such as that illustrated between 2023–2024. For over decadal timeframes, pH and Ωarag will continue to decline with ocean acidification.
Fig 2: The map above shows modeled bottom water pH values. Areas of red indicate a pH above the threshold of 7.8 which is harmful to red king and tanner crab. Areas of blue are below the threshold. The circles represent the preliminary ship-based data collected in the fall of 2024, plotted on the same color bar as the model output. Waters closer to shore are more basic while outer waters are more acidic. The model time period is summer (July-August).
Implications
Based on the sensitivity of red king crab to pH, previous work suggests that ocean acidification may have significant negative impacts to the red king crab fishery (Seung et al., 2015; Punt et al., 2016, Litzow et al 2025). Looking at the data from 2024, the blue color shows that the shallower inner shelf waters that serve as habitat for juvenile red king crab are relatively well buffered (good for crab). Portions of the outer and middle shelf further west contain model pH values less than 7.8 (exceeding thresholds harmful to crab), though not as extreme as in 2023.
The lead author of the OA section was Darren Pilcher at the University of Washington. Co-authors included Jessica Cross with the Pacific Northwest National Laboratory, Natalie Monacci and Esther Kennedy at UAF, and Elizabeth Siddon and Chris Long at NOAA.
A new ESR will be published in December 2025 with updated information from 2025 data collection and modeling.