Applying Regime Shift Indicators to Understand the Potential Impacts of a Multi-Year Cold Event on the Bering Sea Ecosystem
Ecosystems occasionally undergo very abrupt “regime shifts”—such as the simultaneous collapse of crustacean fisheries and boom in groundfish and salmon fisheries that occurred over much of Alaska in the late 1970s and early 1980s. In the past, sudden climate switches have been correlated with these ecosystem regime shifts. It is typically impossible to predict when ecological regime shifts will occur, and we have no ability to predict changes in climate. This lack of predictive ability creates considerable uncertainty for fisheries managers. However, research on early warning indicators for ecosystem regime shifts has been rapidly advancing, offering hope that we may soon be able to detect a situation where an ecosystem is at risk for undergoing a regime shift.
This project applied the new class of early warning indicators to data from a long-running (1982–present) bottom trawl survey of the Bering Sea in order to test for signals of a new ecological response to the recent climate oddity. By applying the indicators to data for about 40 common fish and crustacean species, the project was able to provide information on community-wide resilience in the Bering Sea.
This research is a proactive response to the unusual climate variability in the Bering Sea. A serious problem for fisheries managers is the tendency of ecosystems to show abrupt shifts between alternate regimes in response to external changes. Though rare, these events can have dramatic consequences for Alaska fisheries—an ecological regime shift in the 1970s was marked by widespread collapse in crustacean fisheries and simultaneous booms in groundfish and salmon fisheries. From 2006 to 2013, conditions in the Bering Sea were cold, and the severity and duration of this cold event are unprecedented since the 1976–1977 Pacific Decadal Oscillation regime shift. Such a dramatic ecosystem perturbation suggests an increased chance of an abrupt transition in biological communities. Understanding the ecosystem implications of this cold event is a pressing need for successful management of Alaska fisheries.
Why is this an Alaska Sea Grant project?
This project addresses the Alaska Sea Grant theme on impacts on and strategies for coastal ecosystems and/or coastal communities adapting to change. Ecological effects of natural climate shifts remain a source of risk for the social and economic well-being of coastal communities. This research will use innovative methods from a developing scientific literature to provide earliest-possible warning to fishery managers for potential shifts in the eastern Bering Sea ecosystem.
How will researchers conduct their study?
The development of statistical tools for early detection of ecological regime shifts has been a very active area in recent years. This project utilizes best practices for applying early warning indicators to the NOAA Bering Sea trawl survey time series from 1982 to the present. The indicators that will be tested for, rising spatial variance and spatial correlation in abundance of about 40 species, have previously been demonstrated as reliable predictors for new reorganization events in real-world studies of several marine ecosystems, including the Gulf of Alaska and Bering Sea.
Bob Lauth, Supervisory Research Fishery Biologist for the NOAA Alaska Fisheries Science Center
Stephani Zador, NOAA Alaska Fisheries Science Center
What researchers learned
The analysis that we completed in the first year of this project showed that the early warning indicators, which are expected to signal decreasing resilience in a community under perturbation, were in fact markedly elevated across the Bering Sea groundfish and crustacean community during the 2006–2013 cold anomaly. Furthermore, early warning indicators returned to “normal” levels with the reversion to warm temperatures in 2014. These results support theoretical predictions of how early warning indicators should behave for a community undergoing a persistent perturbation, and are noteworthy for being one of the few tests to date of these indicators in a large, complex ecosystem like the Bering Sea.
Relevance: Alaska fish and crustacean communities have undergone several abrupt reorganizations over the last 70 years, resulting in severe disruption to commercial fishing communities. Developing early detection methods for decreased ecological resilience, and an elevated risk of abrupt ecosystem change, is key problem in the management of Alaska fisheries.
Response: This project uses early warning indicators, a rapidly evolving field in applied ecology, to attempt to measure changes in fish and crustacean community resilience during a multiyear cold anomaly in the Bering Sea.
Results: Our first-year results supported the use of early warning indicators for detecting sudden change in Alaska ecosystems. These results were shared with managers in a contribution to the Ecosystem Considerations chapter of the North Pacific Fishery Management Council SAFE report. Turning early warning indicators into an actual management tool is a goal that is being addressed by many research groups globally, and our results are one contribution to this international effort.
Litzow, M.A., and R. Lauth. 2015. Early warning indicators in the Bering Sea trawl survey. In: Ecosystem Considerations 2015: Status of Alaska's Marine Ecosystems. North Pacific Fishery Management Council, Anchorage, pp. 209-210. https://www.afsc.noaa.gov/REFM/Docs/2015/ecosystem.pdf