Scientific data used to manage global fisheries are often collected within fixed spatial units that reflect relatively static management areas. However, taxa are shifting their distributions beyond their historical ranges as global ecosystems warm with climate change. Many marine fishes are moving to higher latitudes or deeper waters, often placing them beyond the boundaries of their historical scientific survey and management areas. Extending surveys or adding additional data collection points is seldom possible because organizational budgets are constrained and personnel is limited. Accurately tracking where and how many individuals have moved is difficult when fish freely cross historical survey extents or international boundaries. There is a growing need to combine resource-monitoring efforts and promote international partnerships to share information across political borders and scientific survey extents to assess and manage transboundary species.
The Bering Sea region is one example of an ecosystem that is responding to changes in climate and oceanographic conditions. A reduction of sea ice coverage in this system due to warming waters is resulting in weakened water column stratification, reduced and delayed productivity, and removal of a physical barrier of cold, subsurface waters (the cold pool) that previously prevented northward movement of groundfish species. Groundfish such as walleye pollock (Gadus chalcogrammus), Pacific cod (Gadus macrocephalus); and Alaska plaice (Pleuronectes quadrituberculatus) are responding to reductions in sea ice and cold pool extent by changing their distributions, as evidenced by genetic and observational data. These changes can affect commercial and subsistence fishing as well as food web dynamics.
Authors of the most recent Editor's Choice article present a spatiotemporal approach to combine fishery-independent bottom-trawl data from the United States and Russia to create the first-ever model-based index of abundance for walleye pollock, Pacific cod, and Alaska plaice across the Bering Sea shelf. The data used are from the U.S. National Oceanic and Atmospheric Administration's (NOAA) Alaska Fisheries Science Center (AFSC) and Pacific branch of the Russian Federal Research Institute of Fisheries and Oceanography VNIRO (TINRO) and cover the entire Bering Sea shelf region. With this approach, O'Leary et al. investigate the impact of oceanographic conditions on groundfish biomass and uncertainty, as well as the availability or proportion of groundfish biomass within the extent of NOAA AFSCs fishery-independent annual bottom-trawl survey of the eastern Bering Sea. They found that all three groundfish densities shifted northward relative to historical densities, and high-density areas spanned the international border, particularly in years warmer than the long-term average. The findings of the paper suggest that these northward movements are driven in part by changing oceanographic conditions. In 2017, 49% of pollack, 65% of cod, and 47% of plaice biomass were present in the western and northern Bering Sea. These data suggest that groundfish biomass in the eastern Bering Sea is declining.
The methodology developed in this paper combines scientific fishery-independent bottom-trawl data and habitat information in a way that is applicable to other regions where commercially important fish span areas managed by multiple countries or agencies. Improving data availability and collaboration while developing methods to combine surveys is crucial to monitoring the full extent of fish distributions for management, particularly under a changing climate. Data sharing and international collaboration will improve our understanding of the economic and ecological risks of managed species and allow for continued sustainable and accurate management. Coordinated efforts through organizations such as the North Pacific Marine Science Organization (PICES) can serve as platforms to continue data sharing and synthesis for monitoring the movement of these groundfish species to determine the permanency of these shifts in a rapidly changing climate and pan-Arctic system.
Read the full paper, Understanding transboundary stocks' availability by combining multiple fisheries-independent surveys and oceanographic conditions in spatiotemporal models, in ICES Journal of Marine Science.
Editor's Choice articles are always free to read in ICES Journal of Marine Science.
The F/V Vesteraalen in Nome, Alaska, during the summer of 2019. This is one of the vessels used to carry out the NOAA AFSC Bering Sea shelf bottom-trawl survey. © Cecilia O'Leary