Shifting baselines confound river restoration

Lake Erie tributary. Putnam County, Ohio.

How do we set targets for river restoration when we don't know how much the ecology of the system has been altered by human impact?

This is a central question in a recent article in the journal Biosciences that argues that freshwater systems in North America and Australia at the time of European colonization enjoyed a super-abundance of species far greater than many restoration planners realize today. The article authors, Paul Humphries and Kirk Winemiller, use historical accounts to provide evidence of past abundance of fish, mussels, and mammals. For example, they write,

"Eighteenth-century travelers and settlers [in the Ohio River Valley] described the huge numbers of pike, walleye, catfish, buffalofish, suckers, drum, and sturgeon, as well as small fish such as sand darters, chub, riffle darters, and minnows (Trautman 1981). Fish were described as being so numerous that a spear thrown into the water only rarely missed one."

Humphries and Winemiller, also use historical accounts to describe the widespread depletion of species through fishing, hunting, damming, and other anthropogenic causes that followed in the post-colonial era. For example they state,

"Although Native Americans had hunted beavers for millennia, C. canadensis numbers at the time of European arrival were estimated at between 60 million and 400 million. Hunting by Europeans began in the early part of the 17th century, and between 1630 and 1640, 80,000 beavers were harvested per year. The hunting intensity was such that by 1900, the North American beaver was economically and ecologically extinct."

This article joins a growing body of research using historical accounts to warn about the problems of shifting baselines (see Unnatural History of the Sea). Shifting baselines occur when conservation science and practice suffers from collective memory loss about what ecological conditions used to be like and mistakenly assumes that a recently degraded state is the unaffected reference condition. This is likely to occur when widespread human impacts on species predate wildlife population assessments. Humphries and Winemiller contend that as a consequence of shifting baselines, restoration planners underestimate the likely far-reaching effects that freshwater species historically had on ecosystem function.

The authors call for restoration efforts that place greater emphasis on the reintroduction of top predators and keystone species recently extirpated from freshwater systems. They also argue for the creation of freshwater protected areas where restoration experiments on the effects of reintroduced species can be explored.

Source:	BioScience
Title:	Historical Impacts on River Fauna, Shifting Baselines, and Challenges for Restoration
Authors:	a) Paul Humphries, and b) Kirk Winemiller
	a) Charles Stuart University, New South Wales, Australia b) Texas A & M University, College Point, Texas