Widening Diet Breadth, Declining Foraging Efficiency, and Prehistoric Harvest Pressure: Ichthyofaunal Evidence from the Emeryville Shellmound, California

Article excerpt

The Emeryville Shellmound is a famous but now destroyed midden once located on the east shore of San Francisco Bay. Analyses of the fish remains from the stratified late Holocene deposits indicate that prehistoric peoples had substantial impacts on the sturgeon populations of the Bay. This calls into question the commonly held belief that native peoples lived in harmony with nature and has important implications for the management of modern vertebrate populations.

Introduction

Let us begin by briefly suggesting what North America would have looked like to a late-fifteenth-century European who, through some feat of wizardry, could have soared like an eagle across the continent . . . he would be astonished to see streams thick with salmon and shad, or he might gaze with amazement at a thirty-foot-long sturgeon lying motionless in a deep pool next to a shaded bank... He would look with a hunter's eye at the uncountable deer, antelope, elk, bear, and bison, and at the waterfowl that swarmed by the millions... This game, and the fish he could easily pull from the lakes and streams, ... would make up his diet in this pristine new world

SHABECOFF (1993: 3-5)

It is commonly assumed that the distributions and abundances of vertebrate resources recorded during the early historic period in North America reflected a 'pristine' condition. This view follows from the perception that native American population densities and technological capabilities were simply too low to deplete or extirpate vertebrate populations or, alternatively, that native peoples were 'children of nature' and the original conservationists (Redford 1991; Alvard 1994; Kay 1994). In fact, these perceptions underlie modern wildlife management policies and practices. Because pre-Columbian environments are routinely viewed as 'primordial wilderness' (Hewes 1973:150; Shabecoff 1993:3-5), restoring ecosystems to their 'original condition' simply requires the elimination of European influences; this is the principle behind 'hands-off' or 'natural regulation' management (Kay 1994).

This traditional view has, however, been recently challenged on theoretical as well as empirical grounds in several contexts in western North America (e.g. Broughton 1994a; 1994b; Grayson in press; Hildebrandt & Jones 1992; Jones & Hildebrandt 1995; Kay 1994). And since aboriginal human population densities were extremely high in California (e,g. Cook 1976), late Holocene California has been the focus of recent challenges.

In California, recent evidence for human impacts on prehistoric faunas has emerged from analyses of vertebrate remains from late Holocene archaeological sites; these document steadily declining abundances of large-sized prey species from environmentally distinct regions throughout the state (see Broughton 1994a; 1994b; Grayson 1991; Hildebrandt & Jones 1992; Jones & Hildebrandt 1995). Most of these analyses have been conducted in the context of evaluating ecologically oriented models of subsistence change; all have concluded that the documented declines in the archaeological abundances of large prey is a function of expanding prehistoric forager densities and game depletion.

The ecological models that underlie these analyses suggest that late prehistoric subsistence adaptations in California focused on resources that yielded low caloric returns per unit time of procurement and that significant decreases in overall caloric return rates occurred during the late Holocene (Basgall 1987; Beaton 1991; Bettinger 1991; Broughton 1994a; 1994b; Cohen 1981). As human population densities increased steadily during the late Holocene, it is argued, the per capita and/or absolute abundances of such high-return resources as large-bodied terrestrial herbivores decreased. As a result, diets included higher frequencies of such smaller, lower return resources as molluscs, smaller fishes, and acorns. These hypothetical models suggest the occurrence of resource intensification, classically defined as a process by which the total productivity or yield per areal unit of land is increased at the expense of declines in overall caloric return rates or foraging efficiency (Boserup 1965; Earle 1980). …