By Ruth Thurstan and Emily Klein
The shifting baseline syndrome describes the phenomenon where long-term changes in a system, and especially human impacts, go unrecognized because our perception of what is 'natural' shifts with succeeding generations. Shifting baselines are a particular problem for the oceans because in many locations data collection began decades or even centuries after our influence on marine ecosystems did.
Shifted baselines can mask changes in species abundance, distribution, and metapopulation structure, with strong implications for how we manage marine resources and understand ecosystem health. For example, management targets may be set using more comprehensive, but shorter, time-series, or are assessed based on current ecosystem conditions. Both of these can be subject to a shifted baseline if environmental conditions have changed or stock sizes were significantly reduced prior to the start of the time-series being used.
Shifting baselines can also result in misconceptions about species recovery. A species may appear restored given a contemporary and shifted baseline, but historical perspectives may demonstrate the species was previously more abundant or broadly distributed, such as the historical extirpation of spawning or nesting aggregations. Consequently, we may underestimate what recovery should look like, or, as is the case with marine mammals in some regions, ignite debate about whether these species are currently at abnormally high levels. When we are unable to ascertain past population size due to shifted baselines, we cannot know if we have reached targets or how to resolve resulting conflicts.
Implications of the shifting baseline syndrome are increasingly consequential as fisheries management embraces ecosystem-based approaches. While necessary, such approaches require progressively sophisticated analytical techniques, which greatly expands data needs. Such data may only appear available in increasingly narrow temporal windows, exacerbating the shifting baseline syndrome.
How, then, to address shifted baselines? The related literature can imply we should aspire to some 'pristine' condition prior to human impact, but a return to these prior conditions may not be economically or socially desirable. This does not negate the need to address shifting baselines with historical perspectives. Understanding how our baselines have shifted reveals to us what is ecologically feasible, helps fill gaps in contemporary assessment, and provides more realistic, and more hopeful, expectations.
In addition, as we reach further back in time, what becomes obvious is that ecosystems may not have a single 'pristine' state prior to significant anthropogenic impact, but instead have always been changeable and dynamic, with periods of relative stability. Addressing shifting baselines also allows us to perceive system stability and resilience, as well as the natural range of system variability and the pace and direction of change. For example, historical data have helped disentangle some of the confounding influences of climate change and fishing pressure, and provided insight on natural fluctuations. In situations where an ecosystem has been fundamentally altered due to human influence, reversing the shifting baseline syndrome can help us understand how alteration happened, clarify how preferable (and how reachable) alternative states may be, and how we might prevent, or prepare for, future regime change.
Misconceptions due to shifting baselines are not just limited to the ecological side of the social-ecological coin. We also make assumptions about human communities. For example, many of our current assumptions about how people behave are anchored in the 'tragedy of the commons'. Yet over time, fishing communities have demonstrated a wide range of social structures, motivations, and values, including communal and collaborative behavior not predictable with assumptions of selfishness. Expanding our view to include a wider range of communities through time may help us understand contemporary motivations and social structures, with direct bearing on the way we work with and manage these communities. We also tend to view management itself through a shifted baseline, assuming many of our 'modern' management measures, including ecosystem-based approaches, precautionary principles, and spatial closures, are novel. While the terms we use to describe them have been introduced in recent decades, an expanded view reveals these measures have been recommended and used in similar forms for centuries. In the United States, spatial management and ecosystem principles were adopted practice by the late 1800s, while gear regulations and spatial closures in Europe date back to the Middle Ages. Looking back at when the outcomes of these actions were successful as well as what undermined their potential success could help inform future management. Addressing these elements of shifting baselines can help us better assess people and our relationship with marine ecosystems, which can inform the integration of human dimensions (both social and economic), now a core element of the ICES Strategic Plan.
For all of these reasons, addressing shifting baselines is critical for understanding and managing marine social-ecological systems. Although doing so is challenging, it can be achieved by continuing to incorporate historical data and perspectives into marine science resource management. This is not always easy: historical datasets may be viewed as biased and less precise than contemporary data, incompatible with recent time-series, or redundant. There is some basis for skepticism, and scientists are increasingly adopting approaches that adeptly assess and deal with uncertainty and other issues common to historical data. Moreover, ecosystem-based management is facilitating the advent of new techniques and increasing acceptance of using non-traditional forms of data, which may promote further engagement with historical data. The issue of redundancy is also being addressed by work, including publications in the ICES Journal of Marine Science, which demonstrate the application potential of historical data. Finally, fully addressing shifting baselines requires communicating with resource users and the general public, and historical data – particularly narrative or visual information – can play a valuable role.
Although the challenge of addressing shifting baselines remains, emerging analytical and management approaches provide opportunities to apply non-traditional data sources for a long-term perspective, and continued research has helped the phenomenon become more appreciated and accepted. This is an important step forwards, and the Working Group on the History of Fish and Fisheries (WGHIST) exists as a part of the community working to address the shifting baselines syndrome.