Unshifting the baseline: a framework for documenting historical population changes and assessing long-term anthropogenic impacts

Abstract

Ecological baselines-reference states of species' distributions and abundances-are key to the scientific arguments underpinning many conservation and management interventions, as well as to the public support to such interventions. Yet societal as well as scientific perceptions of these baselines are often based on ecosystems that have been deeply transformed by human actions. Despite increased awareness about the pervasiveness and implications of this shifting baseline syndrome, ongoing global assessments of the state of biodiversity do not take into account the long-term, cumulative, anthropogenic impacts on biodiversity. Here, we propose a new framework for documenting such impacts, by classifying populations according to the extent to which they deviate from a baseline in the absence of human actions. We apply this framework to the bowhead whale (Balaena mysticetus) to illustrate how it can be used to assess populations with different geographies and timelines of known or suspected impacts. Through other examples, we discuss how the framework can be applied to populations for which there is a wide diversity of existing knowledge, by making the best use of the available ecological, historical and archaeological data. Combined across multiple populations, this framework provides a standard for assessing cumulative anthropogenic impacts on biodiversity. This article is part of a discussion meeting issue 'The past is a foreign country: how much can the fossil record actually inform conservation?'

Keywords: anthropogenic impacts; ecological baselines; epoch assessments; population depletion; population recovery; shifting baseline.

Figure 1.

EPOCH categories of population change, with respective thresholds (percentage of change in population size in relation to a conceptual baseline in the absence of human actions) and illustrative examples (see electronic supplementary material, table S1 for more details). (Online version in colour.)

Figure 2.

EPOCH assessments of four subpopulations of bowhead whale (Balaena mysticetus): Bering–Chukchi–Beaufort Seas (BCB, Little Changed, 1800 baseline); Okhotsk Sea (OS, Severely Depleted, 1800 baseline); east Greenland–Svalbard–Barents Sea (EGSB, Nearly Extirpated, 1600 baseline); and eastern Canada–west Greenland (ECWG, Moderately Depleted, 1500 baseline). We map separately the region of the Strait of Belle Isle and Gulf of St Lawrence (BISL), which is part of ECWG, as it is no longer occupied (thus mapped as Extirpated). See electronic supplementary material for details. (Online version in colour.)