Historical Impacts on River Fauna, Shifting Baselines, and Challenges for Restoration

A human populations modify the landscapes and eco systems they inhabit, whether by direct exploitation of natural resources or through activities such as damming rivers or introducing alien species (Reynolds et al. 2001, Olden et al. 2008). Although less technologically advanced societies can affect their environments profoundly over time (Pinnegar and Engelhard 2008), especially when colonizing islands, it is typically postindustrial societies that have made the biggest impact on the natural environments of continents (e.g., Crosby 2000). The process of large-scale, dramatic, anthropogenic environmental change had been occurring in western Europe since medieval times, but the major emigration of Europeans during the 17th and 18th centuries to parts of the world that had hitherto been influenced only by indigenous peoples with relatively low population sizes produced rapid and dramatic environmental changes (Crosby 2000). Those colonizers who formed coastal communities looked to the sea for subsistence and, later, for wealth. The environmental cost was huge. Indeed, historical overharvesting of marine animals, including fishes, whales, and oysters, has been implicated in the collapse of coastal ecosystems (Jackson et al. 2001, SaenzArroyo et al. 2006). In each case, a species or stock, such as Atlantic cod or Chesapeake Bay oysters, was harvested to the point of ecological extinction, and the wide-ranging effects of their decimation on food webs are still evident today. Overharvesting, it has been argued, was typically the first environmental disturbance in coastal and estuarine eco systems colonized by postindustrial societies, occurring before severe habitat alteration, pollution, or introduction of alien species (Jackson et al. 2001). But many coastal communities also looked to freshwaters to supplement food from the sea (Vickers 2004), and settlement was by no means limited to coastal regions. European colonists in North America and Australia, in particular, made their way inland relatively early in the colonization process, usually settling near lakes or along rivers (Crosby 2000). Exploitation of freshwater animals began right away: People took advantage of abundant aquatic wildlife, typically moving through a series of steps from subsistence, artisanal, and semicommercial fishing to, finally, fully commercial fisheries (see, e.g., Trautman 1981, Vickers 2004). The largest fish species were targeted most intensely (see, e.g., Rowland 1989, Meengs and Lackey 2005), but other animals became commercially important soon after (Naiman et al. 1988, Anthony and Downing 2001). In virtually every case, overharvesting rapidly devastated stocks of the most economically valuable species. Historical Impacts on River Fauna, Shifting Baselines, and Challenges for Restoration