A trans-Holocene historical ecological record of shellfish harvesting on California’s Northern Channel Islands

Abstract

For over 10,000 years, shellfish were an important food and raw material resource for ancient peoples on California’s Northern Channel Islands. Early Channel Island peoples often focused on large, easy-to-gather intertidal species such as California mussels (Mytilus californianus) and black abalone (Haliotis cracherodii), with later peoples expanding their shellfish economy to include a wider range of species. By the time of European contact (AD 1542–1820) the Island Chumash lived in large, sedentary villages and collected a diverse range of shellfish species by the millions. Although predation by the Chumash and their ancestors affected the size of several key shellfish species, 19th and 20th century commercial harvests targeted specific, high-value species for global markets, bringing several shellfish species (e.g., white [Haliotis sorenseni], pink [Haliotis corrugata], and black abalone) to the brink of extinction. This analysis of shellfish remains from Northern Channel Island archaeological sites tracks the changing role of shellfish in human subsistence economies from Terminal Pleistocene to Historic times. An archaeological record featuring several millennia of relative resiliency under intensive Native American predation suggests that regulated, sustainable, and productive shellfish fisheries can be maintained if balanced and healthy near-shore ecosystems are rebuilt.

Introduction

Over the last several decades, there has been a growing interest in the application of archaeological and other deep historical data for addressing modern environmental issues and helping to better understand the consequences of human decision-making on ancient ecosystems (e.g., Kirch et al., 1992, Crumley, 1994, Redman, 1999). Archaeological data have revealed that ancient human foraging, hunting, and other activities have had profound impacts on many faunal and floral communities for millennia. These anthropogenic alterations extend into the deep past and provide baselines and context for understanding the structure and function of modern ecosystems (Kirch, 2006, Lyman, 2006, Rick and Erlandson, 2008).

This paper synthesizes and analyzes archaeological data on shellfish exploitation from the Northern Channel Islands (Fig. 1), investigating patterns of human interactions with shellfish communities. A wide variety of marine shellfish were important in the diet of Channel Islanders beginning over 12,000 years ago (Rick et al., 2005, Erlandson et al., 2011b). Archaeological evidence from a variety of site types demonstrates that Channel Islanders gathered a diverse set of marine shellfish ranging from large abalones to small snails throughout the Holocene. Although people focused their shellfish subsistence economies on different species at different times, shellfish protein remained a dietary staple despite growing populations, evolving sociopolitical organization, and periodic climatic fluctuations.

In the last 150 years, the rise of commercial shellfish harvesting in southern California has resulted in significant reductions in the biomass and availability of targeted species such as abalones (Haliotis spp.), California spiny lobsters (Panulirus interruptus), and sea urchins (Strongylocentrotus spp.; e.g., Rogers-Bennett et al., 2002). This pattern follows a global trend of overfishing, anthropogenic climate change, and marine pollution that has resulted in a worldwide fisheries crisis, where many of the most economically important fisheries have collapsed or declined (Jackson et al., 2001, Myers and Worm, 2003, Pinnegar and Engelhard, 2008). Trans-Holocene data from the Northern Channel Islands can help provide a deep temporal baseline for shellfish exploitation and put these modern ecological impacts into a historical context (see Erlandson et al., 2008b, Erlandson et al., 2011a., Rick et al., 2008).

Located between 20 and 44 km from the mainland coast, California’s Northern Channel Islands are an excellent laboratory for exploring the relationships between human foraging, natural climate change, and the structure and function of marine ecosystems. An extension of the Santa Monica Mountain range, the island chain includes Anacapa, Santa Cruz, Santa Rosa, and San Miguel (east to west), which range in size from 2.9 to 249 km² (Schoenherr et al., 1999; Fig. 1). The islands are topographically diverse, with mountains and hills, raised marine terraces, deep canyons, and extensive dunes. Separation from the mainland throughout the Quaternary has led to a low diversity of terrestrial flora and fauna, with less than half of the plant species on the mainland occurring on the islands. After the extinction of pygmy mammoths (Mammuthus exilis) about 13,000 calendar years ago (Agenbroad et al., 2005), the largest terrestrial mammals were domesticated dogs (Canis familiaris) and island foxes (Urocyon littoralis) which appeared sometime prior to about 6000 years ago (Rick et al., 2009). Marine ecosystems surrounding the islands are highly productive and ecologically diverse. Rocky intertidal, sandy beach, kelp forest, and other near-shore habitats support a wealth of sea birds, sea mammals, fishes, and shellfish that provided the bulk of subsistence protein for Channel Islanders. Marine shellfish include mollusks, echinoderms, and crustaceans that have been a crucial component of island foodwebs and ancient human subsistence practices and technological adaptations.

Humans first arrived via boats to the Northern Channel Islands at least 13,000 years ago (Johnson et al., 2002, Erlandson et al., 2011b). Hundreds of well-preserved archaeological shell middens and lithic scatters provide tangible evidence of human-environmental interactions from ∼12,200 years ago until historic times (Erlandson et al., 1996, Erlandson et al., 2011b, Rick et al., 2005). When these records are combined with high-resolution paleoecological data from the Santa Barbara Basin (Kennett and Ingram, 1995, Kennett and Kennett, 2000, Kennett et al., 2007), the Northern Channel Islands are one of the best places to study the evolving relationship between humans and marine ecosystems over the longue durée.