Human Impacts on California Mussels from The

HUMAN IMPACTS ON CALIFORNIA MUSSELS FROM THE

HOLOCENE TO THE ANTHROPOCENE: METHODOLOGIES AND

APPLICATIONS IN HISTORICAL ECOLOGY

______

A Thesis

Presented to the

Faculty of

San Diego State University

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In Partial Fulfillment

of the Requirements for the Degree

Master of Arts

Anthropology

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Breana Kristin Campbell

Spring 2016

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DEDICATION

For my Parents.

In every walk with nature one receives far more than he seeks. -John Muir

ABSTRACT OF THE THESIS

Human Impacts on California Mussels from the Holocene to the Anthropocene: Methodologies and Applications in Historical Ecology by Breana Kristin Campbell Master of Arts in Anthropology San Diego State University, 2016

Studies on the Northern Channel Islands have demonstrated that human harvesting of California mussels (Mytilus californianus) caused a reduction in mussel shell length over thousands of years. These studies however, have relied on measuring whole mussels from archaeological sites, which can be rare in archaeological assemblages, limiting chronological and geographic visibility. Using an allometric approach, three regression formulas were developed to determine total shell length from the commonly found hinge portion of a California mussel. Of these three regression formulas one, umbo-width, proved to be statistically reliable and practical for estimating the total shell length from archaeological mussel hinge fragments. Using this method, 2,262 California mussel hinges were measured to determine if a reduction in shell size through time could be identified. These results were compared to modern datasets for California mussel shell length on the Northern Channel Islands. The findings discussed herein provide useful baseline data for resource managers in the coming decades as rising sea surface temperatures and increased ocean acidification threaten this species.

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TABLE OF CONTENTS

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ABSTRACT ...... vi LIST OF TABLES ...... ix LIST OF FIGURES ...... x ACKNOWLEDGEMENTS ...... xi CHAPTER 1 INTRODUCTION ...... 1 Mytilus californianus ...... 2 Overview ...... 4 2 BACKGROUND ...... 6 Natural History of the Santa Barbara Channel ...... 7 Climate ...... 8 Major Environmental Transitions throughout the Holocene ...... 9 Flora and Fauna of the Northern Channel Islands ...... 11 Terrestrial Environment ...... 11 Marine Environment ...... 13 The Cultural History of the Northern Channel Islands ...... 15 The Chumash and their Ancestors ...... 15 Terminal Pleistocene and Early Holocene ...... 17 Middle Holocene ...... 18 Late Holocene, the Protohistoric, and the Mission Periods ...... 19 The Spanish and American Periods ...... 21 3 THEORETICAL APPROACH ...... 23 Historical Ecology ...... 23 Data Collection and Methods of Historical Ecology ...... 25 Historical Ecology in Practice ...... 27

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Case Studies from the Northern Channel Islands ...... 29 4 MYTILUS CALIFORNIANUS ...... 33 Ecology ...... 33 Diet, Reproduction, and Growth ...... 34 Competitors and Predators ...... 35 Ecological Succession ...... 36 Ethnographic Evidence for the Harvesting of Mussels ...... 36 5 ESTIMATING CALIFORNIA MUSSEL (MYTILUS CALIFORNIANUS) SIZE FROM HINGE FRAGMENTS: A METHODOLOGICAL APPLICATION IN HISTORICAL ECOLOGY ...... 38 Introduction ...... 38 Background ...... 41 Materials and Methods ...... 43 Results ...... 48 Discussions and Conclusions ...... 50 6 FROM METHODS TO APPLICATIONS ...... 53 7 TRANS-HOLOCENE HUMAN IMPACTS ON CALIFORNIA MUSSELS (MYTILUS CALIFORNIANUS): HISTORICAL ECOLOGICAL MANAGEMENT IMPLICATIONS FROM THE NORTHERN CHANNEL ISLANDS ...... 55 Introduction ...... 55 Background ...... 58 California Mussel Ecology ...... 60 Methods and Materials ...... 63 Results ...... 68 Discussion and Conclusions ...... 74 8 SUMMARY AND CONCLUSIONS ...... 80 Future Directions ...... 82 REFERENCES ...... 83

LIST OF TABLES

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Table 1. General Attributes of the Northern Channel Islands ...... 7 Table 2. A sample of Vertebrate Terrestrial Animals that have Occupied the Northern Channel Islands ...... 12 Table 3. Common Predators of California Mussels ...... 35 Table 4. California Mussel Shell Sizes (TL) Used in our Study from Both Modern and Archaeological Samples, Derived from Whole Shell Measurements and Regression Formula Predictions Based on Umbo Measurements...... 49 Table 5. Umbo-Width and Umbo-Thickness Method Analysis ...... 68 Table 6. Summary Data for Archaeological Samples of California Mussel ...... 69 Table 7. Modern California Mussel Shell Length Data ...... 69 Table 8. Mean Calculated Shell Length for California Mussels ...... 70 Table 9. Games and Howell Post Hoc Test for San Miguel Island Data ...... 70 Table 10. Games and Howell Post Hoc Test for Santa Rosa Island Data ...... 71 Table 11. Games and Howell Post Hoc Test for Santa Cruz Island Data ...... 71 Table 12. Games and Howell Post Hoc Test for Late Holocene California Mussel Data ...... 72 Table 13. Games and Howell Post Hoc Test for Modern California Mussel Data ...... 72

LIST OF FIGURES

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Figure 1. Map of the southern California Coast and Channel Islands...... 6 Figure 2. Major cultural sequences for the Northern Channel Islands. Source: Braje 2010:12...... 16 Figure 3. Watercolor of a Mytilus californianus shell with labels of several of the physiological features mentioned in the text...... 40 Figure 4. Location map of the Santa Barbara Channel region, the Northern Channel Islands, San Miguel Island, and CA-SMI-232...... 43 Figure 5. Regression plot and the derived regression formula for California mussel shell length versus umbo-width, umbo-length, and umbo-height...... 46 Figure 6. A) Normal P-P plot of regression standardized residuals of mean shell length...... 47 Figure 7. Watercolor of a Mytilus californianus shell with labels of several of the physiological features mentioned in the text...... 61 Figure 8. Approximate locations of archaeological and modern sampling sites...... 65 Figure 9. B. Campbell and S. Duncan collecting size data at an archaeological shell midden on the west coast of Santa Cruz Island, January 2015 ...... 66 Figure 10. Trans-Holocene changes in mean California mussel shell length measurements for 16 Channel Island archaeological components compared to broad scale Holocene SST changes from the Santa Barbara Basin ...... 73

ACKNOWLEDGEMENTS

I would like to thank those who have had a direct impact on the success of this research project. My research was graciously supported by a California State University COAST Graduate Student Research Grant and Travel Grant, the San Diego State University Student Success Fee Research Grant, the San Diego State University Graduate Student Travel Fund, the Inamori Fellowship, the Norton Allen and ASM Affiliates scholarships, and the AGSA travel fund. To Todd Braje, thank you for your guidance, encouragement, support, and patience. You have given me the opportunity to accomplish more than I ever thought possible, and you continue to remind me and all of your students of our potential for success. Drs. Matt Lauer and Brian Hentschel, thank you for contributing your time and imparting your knowledge to me. And lastly to Dr. Seth Mallios and Jaime Lennox, thank you for your unconditional support and mentorship over the past several years. To my cohort and all of my fellow graduate students, thank you for your friendship. Getting to know each and every one of you has made me a better person and a better anthropologist. To the “Braje Bunch”, Linda, Stephanie, and Hannah, we’ve had the best of times together and suffered through some hard times as well. You are three of the most inspiring women I know and I am so glad to have shared this experience with you. Finally, thank you to my family. Dad and Mom, thank you for encouraging me to follow my dreams and for teaching me to never back down from a challenge. Don’t worry Dad, I figured it out and I think I might even understand. Mom, I couldn’t have done this without you. Heather and Cody, I am so thankful to have you both, thank you for being the best siblings in the world and the best support system a person could have. Lastly, Dustin, you have been so wonderful through this entire process. Thank you for your encouragement, support, and love.

CHAPTER 1

INTRODUCTION

Earth’s ecosystems are changing rapidly, driven largely by human activities, including overexploitation of wildlife, habitat degradation, and climate change. These anthropogenic impacts are occurring on such a massive scale that they have fueled the assertion that we now live in the Anthropocene, a new geologic epoch dominated by human influence (Erlandson and Braje 2013; Lightfoot et al. 2013; Steffen et al. 2007). To help understand and confront these environmental challenges, researchers have recognized the need for innovative theoretical and methodological approaches. Broadly defined as the use of paleobiological, archaeological, and historical data, historical ecology has become an increasingly popular framework for addressing the complexities of our modern environmental crises. Historical ecology provides a holistic perspective for long-term ecological change, human-environmental interactions over the longue durée, and a context for conservation (Balée 1998; Crumley 1994, 2007; Redman 1999; Rick and Lockwood 2013). In particular, marine historical ecology has become an important interdisciplinary approach to address the collapse of commercial fisheries and marine ecosystems around the world. For decades, the world’s oceans were believed to be inexhaustible, an attitude that contributed to massive overharvesting and the subsequent collapse of some of the world’s most productive fisheries (Jackson et al. 2001; Pauly et al. 1998). As a result, increased attention has been paid to the growing challenges facing fisheries and marine habitats. However, modern management of these resources has suffered significantly from what has been termed the “sliding baseline syndrome” (Pauly 1995), and more commonly referred to as the “shifting baseline syndrome.” Pauly (1995:430) recognized that with each new generation of scientists, baselines were being established based on the “stock size and species composition” that were identified at the start of that generation’s tenure. This, he argues, is

problematic because these baselines do not account for the hundreds, if not thousands, of years of human harvesting. Modern commercial harvesting of marine resources has not been sustainably managed due to the lack of formal approaches for management and an inability to document long-term ecological changes. Detecting trends in ecosystems is reliant upon recognition of natural versus anthropogenic environmental change and the establishment of well-defined benchmarks against which that change can be measured (Dayton et al. 1998). In order to better manage these ecosystems, deep historical data attained using historical ecological theory and methods can be used to determine the effectiveness of modern management programs and to evaluate the health and structure of marine ecosystems and fisheries. A crucial marine ecosystem for resource management is rocky intertidal habitats. Susceptible to frequent use by humans for recreational and subsistence harvesting (Smith et al. 2008), human foraging in this ecosystem can pose management challenges from both direct harvest and the unintended consequences related to extraction, trampling, and handling of intertidal species. Research also suggests that ocean acidification, rising sea surface temperatures (SST), and increased anthropogenic activity on the coast will likely have a greater, more critical impact on these resources in the coming decades (Gazeau et al. 2007; Helmuth et al. 2006). Jackson et al. (2001) emphasized the modern crisis and potential collapse of coastal ecosystems, further solidifying the need for interdisciplinary research regarding historical exploitation and the current state of marine resources.

MYTILUS CALIFORNIANUS Mytilus californianus (California mussel) have long been a prime target for human foraging in rocky intertidal areas, and are especially vulnerable to anthropogenic and natural impacts. It is likely that ancient hominid shellfish procurement extends back in time some 2.5 to 1.7 million years (Erlandson 2001:312) and the presence of intertidal shellfish species in archaeological contexts increases dramatically in archaeological sites found around the world and specifically in North American sites dating from 12,000 calibrated years before present (cal BP) through European contact (Claassen 1998:2; Erlandson et al. 1996). On the West Coast of North America, California mussels tend to be well represented in archaeological shell midden assemblages. As a result of their relative abundance in archaeological sites, they

have been the subject of numerous studies including shellfish procurement and subsistence strategies (Hudson and Blackburn 1982; Jones and Richman 1995; Kroeber and Barrett 1960; Tartaglia 1976; White 1989) and human impacts on mussel physiology and distribution through time (Braje et al. 2007, 2012a; Erlandson et al. 2008). In addition, their use as ornamental and functional artifacts has also been discussed (Gamble 2008; Hudson and Blackburn 1985; King 1990). Furthermore, in a study conducted by Braje and colleagues (2007), California mussels were identified as the highest ranked available shellfish species during the prehistoric period on the Northern Channel Islands due to the relative ease at which they can be collected, their clustering in large communities, and their extensive habitat range. Despite long-term use by humans and the importance of California mussels to intertidal communities, very little modern data exist regarding the current health and state of this resource. This is likely due to the lack of a perceived threat against California mussels and the more critically threatened state of other intertidal shellfish such as black abalone (Haliotis cracherodii) (Whitaker, personal communication 2013). As part of a bi-yearly survey of marine resources within Channel Islands National Park (CINP), resource managers have only recently begun to systematically collect California mussel shell length data as a proxy for the current health of the population. Archaeologists working on the Northern Channel Islands have long recognized the importance of California mussels to the Chumash and their ancestors. These scholars have contributed a wealth of information regarding their size and availability for over 12,000 years (Braje et al. 2007, 2012a). Despite the significance of these studies, datasets are often limited due to the challenges posed by studying a resource that is not well preserved when recovered from archaeological contexts. Cultural and natural taphonomic processes often cause California mussel shells to become highly fragmented, frequently leaving only the hinge portion intact. With few whole mussels available for reconstructing shell length data, researchers have been limited to small sample sizes of whole shells or have used a template method for estimating the shell length from the breadth of the hinge (White 1989). Recently however, this template was found to be statistically unreliable for estimating total shell length (Bell 2009), highlighting the importance of identifying new, reliable methods of estimating the total shell length of a California mussel.

OVERVIEW Using archaeological and historical ecological methods, my thesis addresses several research questions, including: 1. Do correlations exist between the total shell length of a California mussel and the hinge portion of the shell? 2. Can a reliable regression formula(s) be developed from those correlations, where the r² value is greater than 0.7? 3. When applied to an archaeological sample of California mussels, can the total shell length be adequately (to within 1 cm of known total length) predicted using the regression formula(s)? 4. Do fluctuations in shell length exist throughout the archaeological record for the Northern Channel Islands? 5. Is anthropogenic harvesting or natural climatic change the primary driver of fluctuations in average shell length through time? 6. How does the average shell length of modern California mussels compare to prehistoric size data for the Northern Channel Islands? 7. What trends exist for California mussel shell length through time and how can these data contribute to the discussion of modern management for this species? I have compiled the results of these inquiries into two complementary studies. In the first study, Chapter 5, I have addressed my first three research questions related to the methodological challenges facing California mussel research. Using an allometric approach, I identified three measurements of physical elements found on the hinge portion of the shell and tested them for correlations to the total length. Although all three measurements suggest a strong relationship, one measurement in particular, referred to as umbo-width, proved to be a statistically reliable and practical method for estimating California mussel length. Using this method, I addressed my remaining questions and have included those results in Chapter 7. Using a sample of 2,262 California mussels from 16 archaeological assemblages from the Northern Channel Islands, declines in California mussel shell length during the prehistoric period were identified for San Miguel Island. Interestingly, Santa Rosa Island and Santa Cruz Island did not show declines in mussel shell length from the Middle to the Late Holocene. When compared to modern data, size data from two of the three Northern Channel Islands showed a significant increase from the prehistoric to modern period. This research provides additional baseline data for California mussel populations and offers a framework for future studies of California mussel shell length change through time. This research strategy can also

5 be applied to other shellfish species, including endangered black abalone, which could benefit from studies that not only identify size changes in the past (see Braje 2010; Braje et al. 2015; Erlandson et al. 2008; Rick and Lockwood 2013) but integrate modern data to inform resource managers about long-term trends. These studies have been prepared as manuscripts for submission to peer-reviewed journals or edited volumes and information provided in the subsequent chapters is, at times, necessarily redundant. To complement these studies, I have included a summation of the cultural and environmental background for California’s Northern Channel Islands in Chapter 2. In this chapter, I discuss several concepts, including periods of climatic variability and the role of marine ecosystems during the prehistoric period, specifically the dietary and cultural importance of intertidal shellfish species. Historical ecology provided the theoretical framework through which my methods and conclusions have been contextualized. In Chapter 3, I review the history of this theoretical approach, provide several accepted definitions, and offer supplementary information in the form of a literature review that spans the application and limitations of historical ecology. I conclude the chapter with case studies from the Northern Channel Islands that focus on shellfish. California mussels are the focus of this thesis and in Chapter 4, I provide a review of California mussel ecology, as well as a brief discussion of the ethnographic record as it relates to the procurement of rocky shore, intertidal shellfish. Finally, in the last chapter, Chapter 8, I discuss the implications of my research and suggestions for future directions.

CHAPTER 2

BACKGROUND

Located off the coast of southern California are eight islands, known collectively as the Channel Islands (Figure 1). With their complex ecosystem and histories, these islands have long drawn interest from scientists, researchers, and the general public. The geographic position of the Channel Islands and localized marine upwelling provide a nutrient-rich ecosystem that sustains an abundance of distinctive flora and fauna that inhabit local land and seascapes. The rich natural history of the Channel Islands is matched by an equally impressive cultural history. As a result, these islands have been featured in a vast collection of peer-reviewed journals, edited volumes, and works of fiction and non-fiction (see Arnold 1987, 1990, 1992, 2001; Boyle 2011; Braje 2010; Erlandson 1994; Rick 2007; Orr 1968).

Figure 1. Map of the southern California Coast and Channel Islands.

What follows is a brief introduction to the Santa Barbara Channel region. The environmental and cultural history of all eight Channel Islands is rich and diverse and cannot be adequately explored here; therefore, I focus solely on the Northern Channel Islands to provide the cultural and natural context for my research. First, I briefly discuss the geographic location, geologic features, and climatic conditions, as well as terrestrial and marine resources. Second, I review the prehistoric occupation of these islands by the Chumash and their ancestors and briefly describe the ranching and abalone fishing industries that took place on the islands during the Historic Period. In closing, I discuss the ownership and management of these islands today.

NATURAL HISTORY OF THE SANTA BARBARA CHANNEL The Channel Islands are commonly divided into northern and southern groups. The northern group consists of Anacapa, Santa Cruz, Santa Rosa, and San Miguel, while San Clemente, Santa Catalina, San Nicolas, and Santa Barbara comprise the southern group. The islands are managed by several private and federal agencies, including but not limited to: the National Park Service (NPS), the Nature Conservancy, and the United States Navy. Unlike the coastal landscapes of the mainland, the Channel Islands are relatively free of large scale development. This lack of urban sprawl has left much of the biota undisturbed and the archaeology in pristine condition.

Table 1. General Attributes of the Northern Channel Islands Distance Maximum from Number of Number of Elevation Mainland Land Native Plant Island Area (km2) (m) (km) Mammals Taxa Anacapa 2.9 283 20 2 190 Santa Cruz 249 753 30 12 490 Santa Rosa 217 484 40 4 387 San Miguel 37 253 42 3 198 Sources: Power 1980, Schoenherr et al. 1999, and Braje 2010.

The Northern Channel Islands range in size from 2.9 to 249 km² and are situated between 20 and 42 km from the mainland (Table 1). Unlike the southern islands, which are widely dispersed and isolated, the northern islands are relatively close together and are an extension of the Santa Monica Mountains (Weaver 1969). The bathymetry surrounding the

islands suggests that during the last glacial maximum (LGM), when sea levels were much lower than they are today, the northern islands comprised one large island, Santarosae, that could be traversed on foot (Kennett 2005; Orr 1968). As eustatic sea levels rose between 18,000 and 7,000 cal BP, low-lying portions of Santarosae were inundated by the Pacific Ocean, reducing island landscapes by nearly three quarters (Porcasi et al. 1999; Reeder- Myers et al. 2015). Today, Santarosae is separated by sea passages that divide the island into four smaller islands, San Miguel, Santa Rosa, Santa Cruz, and Anacapa. The islands are rich in geologic resources including volcanic and sedimentary rock types, which can be manufactured into stone tools. Quarries of Monterey, Cico, Wima, and Santa Cruz Island chert, as well as sandstone and other metavolcanic rocks can be accessed and/or traded amongst the islands. Stone resources were used to manufacture a variety of tools and ground stone bowls (Conlee 2000). Monterey chert from Santa Cruz Island supplied the most valuable stone material and was used extensively during the Late Holocene to manufacture the trapezoidal drills necessary for the production of Olivella (purple olive snail) beads. Asphaltum (bitumen) seeps supplied a source of natural glue or sealant used for waterproofing baskets, grass-weaved water bottles, and plank canoes or tomols (Braje et al. 2005). The geologic resources of the islands provided many of the necessary raw materials used by the Chumash to develop their specialized tool kit and ornamental objects.

CLIMATE The Santa Barbara Channel region has a Mediterranean climate, with cool, wet winters and warm, dry summers (Smith 1952). Due to maritime conditions, the offshore islands generally experience a mild climate relative to the California interior (Kennett 2005). Historical and modern air temperature data recorded for Santa Cruz Island suggest the islands remain relatively cool (average 15.8 ˚C/ 60.4 ˚F), with temperatures peaking from June through October (Junak et al. 1995). Fluctuations in air temperature on San Miguel and western Santa Rosa islands are influenced by strong winds and fog (Kennett 2005). Precipitation records for Santa Cruz Island from 1972 and 1982 suggest that island rainfall is highly variable (Junak et al. 1995), which restricts the availability of drinking water. The two larger islands, Santa Cruz and Santa Rosa, have the greatest number of drainages, springs, and streams. Today, Anacapa and San Miguel have very little potable water; however, water

availability tends to be correlated to the presence of vegetation on the islands. Throughout the historical ranching period on the Channel Islands, much of the native vegetation was eradicated and replaced by introduced grasses. Since the removal of historically introduced domesticated animals, the native and endemic flora communities and island hydrological systems have begun to recover, suggesting that these islands may have been less depauperate than previously believed (Rick et al. 2014).

MAJOR ENVIRONMENTAL TRANSITIONS THROUGHOUT THE HOLOCENE The terminal Pleistocene and Holocene were particularly unstable climatic intervals, with at least six periods of rapid changes in global climatic conditions (Mayewski et al. 2004). The Santa Barbara Channel region is no exception with climatic conditions varying considerably over the past 13,000 years (Kennett 2005). The geographic orientation of the channel provides a uniquely detailed record of the region’s climate throughout the Holocene. Paleo-climate data including, SST and marine productivity, have been collected by Kennett and Kennett (2000), who used data recovered from coring, sediment deposits, and oxygen isotopic analysis of planktonic foraminiferal species to produce a high-resolution Holocene climate record for the Santa Barbara Basin (Kennett 2005:64). These data indicate that periods of long-term drought and fluctuations in SST led to variations in marine resource productivity, including changes in kelp forest coverage, which would have had profound implications for the inhabitants of the southern California region (see Jones et al. 1999). It has been inferred that environmental fluctuations likely led to the rise of socio-politically complex hunter-gatherer societies, including the Island Chumash, who established a massive trade economy, possibly to mitigate environmental pressures (Colten 1993). The transition from the terminal Pleistocene to the Early Holocene (13,000 to 7,500 cal BP) was dominated by generally increasing air temperatures. This warming had a direct impact on shaping the landscape of the Northern Channel Islands. It was during this period of glacial retreat that eustatic sea levels rose and the low-lying portions of Santarosae became inundated, causing the island to separate into four smaller islands divided by ocean passages. Additionally, the rising seas created a series of estuaries found on the coastal mainland and one on eastern Santa Rosa Island. These areas became settlement hubs for foragers to exploit

estuarine shellfish species (Erlandson 1994; Rick, Kennett, and Erlandson 2005). The terminal Pleistocene through the Early Holocene has been characterized as a period of relatively cool temperatures and wetter conditions than seen today. The Middle Holocene (7,500 to 3,500 cal BP) was a period of several environmental changes. Until 7,000 cal BP, sea levels continued to rise at rapid rates eventually slowing to a more gradual rise similar to what is seen today (Berger 1983; Inman 1983). Dry, arid conditions during this period likely led to a greater scarcity of fresh water on the islands as well as changes in plant and animal distribution. Extended periods of warming including intense droughts have also been identified, making already harsh conditions more difficult. Analysis of pollen samples from Santa Rosa Island suggests that fire events occurred at a higher frequency beginning 5,000 cal BP, which Anderson et al. (2010) suggests is the result of increased biomass and anthropogenic burning activity by the Chumash. Throughout the Late Holocene (3,500 cal BP to present), climatic conditions remained relatively consistent. However, when compared to the Early and Middle Holocene, the past 3,500 years have been characterized as having much higher instances of intense periods of climatic variability, including one of the coldest periods of the Holocene epoch (Kennett and Kennett 2000). Although the impacts of climate on marine and terrestrial productivity are debated, researchers do agree that SST appears to have been extremely cold between 1,500 to 500 years ago (Kennett and Kennett 2000). Periods of drastic ocean cooling during the Late Holocene have also been associated with increased aridity and known periods of drought on the California coast (Stine 1994). Two periods of climate instability have been of great interest to archaeologists working on the Channel Islands: the Middle to Late Transitional (MLT) period between AD 1150 and 1300 (Arnold 1992) and the Medieval Climatic Anomaly (MCA) between AD 800 and 1350 (Kennett and Kennett 2000; Raab and Larson 1997). It was during these intervals that several years of intense drought likely led to the rise of socio-political complexity within Chumash society, which will be discussed in greater detail later in the chapter. Until recently, sea level rise has remained gradual, however the impacts of anthropogenic climate change on glacier melt has caused sea levels to rise at a much faster rate and has led to major concerns for the future of low-lying coastal areas (Meier et al. 2007; Scambos 2011) and the preservation of coastal archaeological sites around the world.

FLORA AND FAUNA OF THE NORTHERN CHANNEL ISLANDS

Terrestrial Environment The southern California coast and inland regions are comprised of a wide variety of productive flora and fauna species including acorn, pine nuts, chia seeds, deer, rabbits, and other plant and mammal species (Schoenherr 1992; Smith 1998). Relative to the coastal and inland mainland, the Northern Channel Islands have an impoverished terrestrial landscape, with limited native flora and fauna species distributed across the islands (Schoenherr et al. 1999). Despite this relatively impoverished landscape, the Channel Islands are home to 145 species of terrestrial plants and animals that are endemic to the region, including blue dicks (Dichelostemma pulchellum), which may have been an important source of carbohydrates for island communities. The Northern Channel Islands lack many of the large terrestrial mammals available on the mainland. The recovery of pygmy mammoth (Mammuthus exilis) remains on the islands confirm their presence prior to 13,000 years ago (Orr 1968), but there is no evidence to suggest pygmy mammoths and humans occupied the islands concurrently. However, temporal data, including high-resolution radiocarbon dating, has closed the gap in occupation to within 1,000 years (Johnson et al. 2000). The largest land mammal to occupy the islands throughout much of the Holocene is a diminutive species of mainland fox known commonly as the Channel Island fox (Urocyon littoralis). How the island fox came to inhabit the Channel Islands is under debate (Hofman et al. 2015; Rick et al. 2008; Vellanoweth 1998). However, in a recent study by Hofman and colleagues (2015), accelerator mass spectrometry (AMS) radiocarbon dating, genetic sequencing, and isotopic analysis suggest that these animals were not present on the islands prior to the arrival of the Chumash. Additionally, the island spotted skunk (Spilogale gracilis amphiala) and the island deer mouse (Peromyscus maniculatus) are endemic to the Northern Channel Islands (See Table 2 for representative sample of land mammals found on the Northern Channel Islands). Endemic lizards and salamanders are also present.

Table 2. A sample of Vertebrate Terrestrial Animals that have Occupied the Northern Channel Islands Endemic, Native, Scientific Name Common Name Island(s) Introduced Occasional Urocyon littoralis San Miguel Island littoralis Fox SMI Endemic Peromyscus maniculatus San Miguel Island streatori Deer Mouse SMI Endemic Urocyon littoralis Santa Rosa Island santarosae Fox SRI Endemic Peromyscus maniculatus Santa Rosa Island santarosae Deer Mouse SRI Endemic Reithrodontomys Santa Cruz Island megalotis santacruzae Harvest Mouse SCRI Endemic Peromyscus maniculatus Santa Cruz Island santacruzae Deer Mouse SCRI Endemic Urocyon littoralis Santa Cruz Island santacruzae Fox SCRI Endemic Spilogale gracilis amphialus Island Spotted Skunk SRI, SCRI Endemic Peromyscus maniculatus Anacapa Island Deer anacapae Mouse A Endemic Myotis evotis Long-eared Bat SCRI Native Occasional Antrozous pallidus Pallid Bat SCRI Native Townsend’s Big- Corynorhinus townsedii eared Bat SCRI Native Eptesicus fuscus Big Brown Bat SCRI Native Occasional Lasionycteris noctivagans Silver-haired Bat SCRI Native Occasional Lasiurus cinereus Hoary Bat SCRI Native Occasional Mexican Free-tailed Tadarida brasiliensis Bat SCRI Native Occasional SMI, SRI, Myotis Californicus California Bat SCRI Native Odocoileus hemionus Mule Deer SRI Introduced Wapiti (Roosevelt Cervus elaphus Elk) SRI Introduced Bos taurus Cattle SRI, SCRI Introduced Equus caballus Horse SRI, SCRI Introduced Canis familiaris Domestic Dog SRI, SCRI Introduced Felis domesticus House Cat SRI Introduced Sus scrofa Pig SRI, SCRI Introduced SMI, SCRI, Ovis aries Domestic Sheep A Introduced Rattus rattus Black Rat SMI, A Introduced Lepus europaeus European Hare A Introduced Note: San Miguel Island (SMI), Santa Rosa Island (SRI), Santa Cruz Island (SCRI), Anacapa Island (A). Source: Schoenherr et al. 1999

Much like the terrestrial fauna, plant communities are less diverse than those found on the mainland. However, the limited number of large game species likely made terrestrial plants an important resource for the Chumash and their ancestors. Island plant communities are patchy and vary in availability across the islands. The larger islands, Santa Cruz and Santa Rosa, exhibit greater plant diversity. Terrestrial biodiversity on the Channel Islands is directly correlated to island size, with the smaller islands exhibiting less diversity than the larger islands (Moody 2000). Philbrick and Haller (1977) identified nine plant communities on the Northern Channel Islands including: southern beach and dune, coastal bluff scrub, coastal sage brush, island chaparral, valley and foothill grassland, oak woodland, southern riparian woodland, pine forest, and coastal marsh. Five additional communities were identified on Santa Cruz Island including: coyote brush scrub, freshwater seeps and springs, vernal ponds, riparian herbaceous vegetation, and mule fat scrub (Junak et al. 1995). A survey conducted by Wallace (1985) identified 848 flora species on the eight Channel Islands and Guadalupe Island in Mexico. Of these 848 species, 227 were determined to be of non- native origin. During the Historic Period, many non-native floras were introduced to the islands, including fennel (Foeniculum vulgare) and Harding grass (Phalaris aquatic) (Knapp et al. 2009).

Marine Environment The marine environment of the Santa Barbara Channel region is incredibly productive. Kelp beds and rocky and sandy nearshore habitats are home to numerous species of pinnipeds, fish, and shellfish; however, spatial and temporal distribution of these resources is not uniform (Kennett 2005). The rich marine environment is likely the result of multiple sea and air currents, countercurrents, and eddies coming together, which creates a localized nutrient-rich upwelling. These phenomena support large communities of phytoplankton, zooplankton, and larvae, as well as extensive offshore kelp beds. Kelp beds in the Santa Barbara Channel region include giant kelp (Macrocystis pyrifera) and bull kelp (Nereocystis luetkeana) species, which provide nutrients as well as shelter for a wide variety of fish and sea mammals. Over 900 fish species have been identified in the Santa Barbara Channel (Love 1996). Many of these species appear in the archaeological record, including California sheephead

(Semicossyphus pulcher), rockfish (Sebastes spp.), and sculpin (Cottidae). Pinniped (seals and sea lions) and cetacean (whales, porpoises, etc.) populations also thrive in the waters that surround the Channel Islands. Point Bennett, located on the far western end of San Miguel Island, is one of the most productive and diverse pinniped rookeries in the world (DeLong and Melin 2000). Six different pinniped species visit the area annually, each of these species appear in the archaeological record and are relatively more common in Late Holocene assemblages. Cetacean species also appear in the archaeological record and occasionally whales become stranded on Channel Island beaches and were scavenged by the Chumash. Seabirds are also commonly found on the islands, with some species residing more permanently and others migrating to the region to breed. Prince Island and Castle Rock, islets located off of San Miguel’s north coast, are breeding grounds for 14,000 and 15,000 birds each year respectively (Schoenherr et al. 1999). Cormorants (Phalacrocorax spp.), brown pelicans (Pelecanus occidentalis), and gulls are commonly found on the Channel Islands. Additional bird species identified in the region include the Western Snowy Plover (Charadrius alexandrinus nivosus) and the bald eagle (Haliaeetus leucocephalus), which was eliminated from the islands during the 1950s and have only recently been reintroduced (Garcelon et al. 1989). Although the extent to which birds may have been of dietary importance to the Chumash and their ancestors is uncertain, research suggests that bird bone was often used to make tools including gorges, pins, and awls (Rick 2004, 2007; Rick et al. 2001). Shellfish species located in intertidal and sandy beach habitats in southern California and, more specifically, on the Channel Islands, are diverse and abundant. Archaeological shell middens found on the islands suggest that these resources played a key role in the diet of the Chumash and their ancestors. Rocky intertidal shellfish including California mussel, red and (Haliotis rufescens) and black abalone, owl limpets (Lottia gigantean), black turban snails (Tegula funebralis), and other small chitons and gastropods are some of the most common species identified in these deposits. Estuarine shellfish, including Pismo clams (Tivela stultorum) are also present on the islands, although not as widely available across space and through time. Additionally, shells were commonly used to make tools and ornamental artifacts including fishhooks, beads, and pendants (Hudson and Blackburn 1985). Callianax biplicata (purple olive snail), until recently classified as Olivella biplicata

(hereafter referred to as Olivella, as it is still commonly referred to in the discipline of archaeology), are also readily available on the islands and were used throughout the Holocene to manufacture beads (Carlton 2007). It is likely that additional taxa not observed today may have frequented the region prior to and after the arrival of humans. The local extinction of sea otters (Enhydra lutris) during the Historic Period (Ogden 1941) and bald eagles in the 1950s (Garcelon et al. 1989) are just two examples of human-driven extinction from this region. Despite the intense harvesting of the world’s ocean resources over the last three centuries and many more centuries of relatively small scale harvest by indigenous groups, this region maintains a highly productive marine environment. The wealth of dietary resources and raw materials in the Santa Barbara Channel region provided for the development of the rich political and economic cultural traditions of the Chumash, their ancestors, and their neighbors.

THE CULTURAL HISTORY OF THE NORTHERN CHANNEL ISLANDS

The Chumash and their Ancestors The prehistoric and historical record for the Santa Barbara Channel region is rich in cultural history. Archaeological research spanning nearly a century has yielded an abundance of data and insight into the prehistoric lifeways and adaptations of the Island Chumash and their ancestors. Due in large part to the lack of burrowing animals and urban development, the preservation of archaeological deposits on the islands is exceptional when compared to that of the coastal mainland. The identification of terminal Pleistocene sites such as Daisy Cave and the Cardwell Bluffs sites on San Miguel Island and Arlington Springs and CA-SRI- 512 on Santa Rosa Island provide researchers with some of the earliest evidence for maritime adaptation in the Americas (Erlandson et al. 1999; Erlandson, Rick, Braje, Casperson, Culleton, Fulfrost, Garcia, Guthrie, Jew, Kennett, Moss, Reeder, Skinner, Watts, and Willis 2011; Johnson et al. 2000). The Chumash and their ancestors have occupied the Santa Barbara Channel for at least 13,000 years (Erlandson et al. 1996) and several chronologies have been suggested for the region (Figure 2). For the purposes of my research I will draw most heavily from the chronologies suggested by Arnold (1992) and Erlandson and Colten (1991). Chumash culture

14C Erlandson and Colten Calendar Years King (1990) Arnold (1992) (1991) Years Phase AD 1782 Historic 3

Phase Late 2 AD 1300 Period Late Period Phase AD 1150

AD 1 Middle to Late 1000 Phase Transition 5 Phase Late Holocene AD 980 4 AD 580 Middle Phase

Period 3 AD 0 Middle Period 800 BC Phase

Phase 1500 BC 1

Phase Z 2850 BC

Middle Holocene

3000 Phase Early Period 5050 BC BC Y

Early Period Phase

Early Holocene

Terminal Pleistocene 8000 BC 8050 BC Figure 2. Major cultural sequences for the Northern Channel Islands. Source: Braje 2010:12.

has been thoroughly examined in many texts; therefore I will focus on the artifact assemblages used to mark the transition from the terminal Pleistocene and Early Holocene

through the Historic Period. I also discuss dietary changes throughout the Holocene and briefly recount the most significant cultural developments from the Chumash and their ancestors’ history.

Terminal Pleistocene and Early Holocene Identifying the exact moment when the Northern Channel Islands were first occupied is impossible. The rising sea levels of the Holocene epoch have likely destroyed many low- lying terminal Pleistocene and Early Holocene coastal sites. Despite this challenge, over 60 sites in excess of 7,000 years old have been identified (Erlandson 1994; Erlandson et al. 2004; Rick, Erlandson, Vellanoweth, and Braje 2005). The artifact assemblage for this period is relatively limited. Chipped stone is rare in sites of this age when compared to the mainland; however projectile points, knives, and drills have been identified (Erlandson 1994; Erlandson, Rick, Braje, Casperson, Culleton, Fulfrost, Garcia, Guthrie, Jew, Kennett, Moss, Reeder, Skinner, Watts, and Willis 2011). Bone gorges (bi-pointed fishhooks) and sea grass cordage recovered from Daisy Cave on San Miguel Island provide evidence for an early fishing adaptation in the region and chipped stone stemmed points and crescents have been found in a number of deposits dated to more than 8000 years (see Braje 2010; Erlandson, Rick, Braje, Casperson, Culleton, Fulfrost, Garcia, Guthrie, Jew, Kennett, Moss, Reeder, Skinner, Watts, and Willis 2011). Although ornamental objects are rare for this period, Olivella spire-removed beads have been found in numerous Early Holocene sites, (Braje 2010; Braje et al. 2005; Erlandson 1994; Erlandson, Braje, and Rick 2005; Vellanoweth et al. 2003). Most Early Holocene sites are dominated by rocky intertidal shellfish including California mussels, owl limpets, and abalone. While the importance of fish, birds, and marine mammals is relatively unknown, an analysis of the Daisy Cave and CA-SRI-512 fauna suggests that fish, birds, and marine mammals played a much greater role in the diet of early Channel Islanders than once believed (Braje 2010; Erlandson, Rick, Braje, Casperson, Culleton, Fulfrost, Garcia, Guthrie, Jew, Kennett, Moss, Reeder, Skinner, Watts, and Willis 2011; Rick et al. 2001). Although our understanding of the Early Holocene occupation of the Northern Channel Islands is limited, archaeological work continues to contribute new insights.

Middle Holocene Until recently, the archaeology of the Middle Holocene has received far less attention than both the earlier and later occupation periods on the islands. An increase in sites radiocarbon dated to between 5,000 and 4,000 years ago suggests a surge in island populations during this time. These sites are distributed across the coastal and interior landscape (Kennett, D.J., B.J. Culleton, J.P. Kennett, J.M. Erlandson, and K.G. Cannariato 2007; Kennett, D.J., J.P. Kennett, J.M. Erlandson, and K.G. Cannariato 2007). It is also during this period that the first sedentary villages appear on the mainland and the first semi- subterranean houses appear on the Channel Islands. Unlike the increased sedentism that occurs on the mainland, however, island populations appear to have remained fairly mobile (Glassow 1997). Much of the artifact assemblage recovered from Middle Holocene sites is consistent with that of the Early Holocene; however, artifacts including side-notched points, composite bone fishhooks, and the first appearance of the mortar and pestle have been used to delineate this period (Erlandson 1997; Glassow 1997; King 1990). In addition, chipped stone stemmed points and crescents fall out of the archaeological record around 8000 years ago. Rocky intertidal marine fauna generally dominate archaeological deposits from the Middle Holocene. Shellfish, including mussels, abalones, chiton, limpets, and other rocky shore taxa are especially common (Vellanoweth et al. 2006). Large red abalone shells are also commonly found in archaeological sites from the Middle Holocene. The appearance of red abalone in sites of this age has been an important topic for researchers because they are typically found in subtidal zones which require harvesters to dive to collect them. Glassow (1993) has argued that this species may have reached intertidal zones as a result of cooler SSTs, making them much easier to collect from the shoreline. Alternatively, Sharp (2000) proposed that red abalone may have been harvested by a select group of sub-tidal divers, while Erlandson, Rick, Estes, Graham, Braje, and Vellanoweth (2005) suggest human predation of sea otters, the main predator of red abalone, may have allowed for the release of red abalone populations outside of their known habitat range (see also Braje et al. 2009). Walker and Erlandson (1986) identified a rise in the presence of dental caries during this period, which suggests an increased reliance on terrestrial plants. Despite this increase in

terrestrial plant consumption the archaeological record does not suggest a decline in the consumption of marine resources. The intricacies of Chumash culture during this period are not well-known (Kennett, D.J., J.P. Kennett, J.M. Erlandson, and K.G. Cannariato 2007). What little knowledge researchers have of ceremonial and social life during the Middle Holocene has been inferred from burials, some of which include elaborate offerings of beads, fishhooks, and effigies (King 1990). The absence of elaborate infant burials suggests that leadership roles were not inherited but instead earned as a result of actions during one’s lifetime (Kennett 2005). The recovery of artifacts manufactured from raw materials that cannot be locally sourced indicates that island groups maintained relationships with groups on the coastal mainland, likely through marriage alliances (King 1990; Orr 1968; Rick 2007). What is known about the people who lived during this time is that they were exceptionally skilled at crafting tools and ornaments from various raw materials and were highly skilled fisherfolk. These traditions provided the foundation for the development of the complex Island Chumash culture that has enthralled researchers for over a century.

Late Holocene, the Protohistoric, and the Mission Periods Much of the archaeological research on the Channel Islands has focused on the Late Holocene and the development of the political and economic complexity of the Chumash and their neighbors. Many cultural hallmarks associated with the Chumash were introduced during this period, including the circular fishhook, plank canoes (tomols), Olivella cup beads, the bow and arrow, and the harpoon (Arnold 1995; Erlandson and Rick 2002; Gamble 2002; Glassow 1996; King 1990; Rick at al. 2002). The Late Holocene is often separated into smaller periods (see Figure 2) delineated by changes in artifact assemblages and/or corresponding to periods of environmental changes, such as severe drought. The social and political elaboration of the last 1,500 years has received the most attention from scholars (Arnold 1990, 1991, 1992, 1993, 2004; Kennett and Conlee 2002; Larson et al. 1994; Raab and Larson 1997). Many studies suggest an extended period of drought and elevated SST, which occurred from approximately AD 1150 to 1300 and led to a major reorganization of Chumash society.

The Chumash continued to exploit the rich kelp beds and rocky nearshore habitats similar to the way they had for over 7,000 years. Kennett (2005) determined that during the Late Holocene fish began to play a much more substantial role in Chumash diet. After analyzing faunal assemblages from sedentary villages, Kennett (2005:175) found that many sites were “overwhelmingly dominated by fish bone.” Fish exploitation varies across space and time; local ecological conditions and variations in SST likely account for the different species recovered from archaeological sites (Kennett 2005). Many of the fish species found in early Late Holocene deposits are from nearshore habitats; by the MLT, fish from the midwater to open ocean zones appear in the Santa Cruz Island archaeological record (Pletka 2001). The development of fishing technologies such as the circular fishhook and toggling harpoon played an important, if not necessary, role for the expansion of the Chumash diet. The development of Chumash cultural complexity tends to be most associated with the Late Holocene. Many researchers have analyzed various religious practices (Hollimon 2004), craft specialization (Arnold 2001; Graesch 2004), and the highly intricate and labor intensive Olivella shell bead production and trade that is emblematic of the Island Chumash culture (Arnold and Graesch 2001; Graesch 2004; Pletka 2004). The point at which the Chumash began to exhibit and develop a socio-politically complex culture is unknown. Some have argued that this transition was gradual, while others suggest a more punctuated model. Erlandson and Rick (2002) suggests that a combination of both models is more likely. Most models suggest that socio-political complexity developed in the Santa Barbara Channel region during the MTL transition period, when SSTs were cold and drought spread throughout the region (Kennett and Kennett 2000). The Chumash were forced to coalesce into large coastal villages, where hereditary chiefs exerted political authority. To deal with large populations and the lack of terrestrial resources, the Island Chumash produced Olivella shell beads by the millions that were traded to the mainland via tomols for acorns or terrestrial mammal meat (Arnold 2001; Kennett 2005). By the time Juan Rodríguez Cabrillo arrived on Santa Catalina and San Miguel islands in AD 1542-1543, the Chumash were living in sedentary villages comprised of dome-shaped houses (Gamble 1995) and were governed by hereditary chiefs (Arnold 1992). After the arrival of Cabrillo and his soldiers, the Chumash remained on the Northern Channel Islands until AD 1822, after which of the remaining Island Chumash were removed

from their island homes and brought to Spanish missions and towns on the California mainland. About 1,270 Island Chumash were baptized at missions in the Santa Barbara and Ventura areas (Johnson 1999). Johnson (1982) inferred that by this time the island populations had dwindled substantially from precontact levels which likely numbered in the thousands. The number of archaeological sites radiocarbon dated to after the arrival of Cabrillo drops dramatically by 76 percent; this decline has been associated with the introduction of Old World diseases spread by Cabrillo and his men (Rick 2007). Despite the devastating effects of missionization on the Chumash, there is considerable evidence to suggest that aspects of Chumash culture and society persisted through the Historic Period (Deetz 1978). Following the removal of the Island Chumash to the mainland, a new wave of settlement occurred on the islands with the arrival of ranchers and various ethnic fisher groups looking to harvest the rich resources from the Santa Barbara Channel region.

The Spanish and American Periods After the removal of the Chumash in AD 1822, the Channel Islands were quickly absorbed into the colonial economies of the early to mid-nineteenth century (Braje 2010). The marine ecosystem suffered tremendous loss as a result of the commercial hunting of sea otters, whales, pinnipeds, and sea birds (Bartholomew 1967; Scammon 1968). Beginning in the early 1850s, immigrant Chinese fishermen began to exploit the abundant black abalone communities on the islands, an exceptionally productive fishery due to the local extinction of sea otters and the disruption of Native economies (the two primary predators of abalone in southern California). The Chinese abalone fishery was a highly sophisticated enterprise with intertidal black abalone harvested systematically across the southern and northern islands and the meat dried and shipped to local Asian markets in the American West and overseas (Bentz 1996; Braje and Bentz 2015). All of the islands, save Anacapa, experienced intensive ranching operations during the nineteenth and twentieth centuries; it is during this time that many non-native species, both flora and fauna, were introduced. De-vegetation by grazing cattle, sheep, and other domesticated herbivores led to widespread erosion on the islands and has caused extensive damage to archaeological sites (Johnson 1980; Rick et al. 2014). In 1938, Santa Barbara and Anacapa islands became the Channel Islands National Monument (Braje 2010). Over time, other islands became protected by public or private

landholdings. Santa Rosa and a portion of Santa Cruz were purchased by the National Park system and, in 1980, the Channel Islands National Park was established. San Miguel is owned by the U.S. Navy, but administered by Channel Islands National Park. In 1999, a network of marine reserves around San Miguel, Santa Rosa, Santa Cruz, Anacapa, and Santa Barbara islands was established to promote biodiversity and sustainable fisheries (Braje 2010). Today, many of the introduced terrestrial animals (see Table 2) have been removed from the islands in an effort to restore the Channel Islands to their prehistoric state. Interdisciplinary research conducted over the past three decades, and more intensely over the past 15 years, has identified how land and seascapes of the islands have been altered by human activity through time. This research has provided resource managers with new data to help direct conservation efforts and to better manage the rich natural and cultural resources of the Channel Islands.

CHAPTER 3

THEORETICAL APPROACH

Anthropologists have long studied cultural-environmental issues from a variety of theoretical frameworks (e.g., Binford and Binford 1968; Butzer 1971, 1982; Dincauze 2000). The environmental movements of the 1960s and 1970s spurred the development of new and innovative theoretical and methodological approaches to assess and explain the complex, dialectical relationships between humans and environments. Out of this period of environmental awareness grew an interdisciplinary framework that has since been applied to a variety of contexts and is now used widely by researchers across diverse disciplines. What follows is a summary of the development and use of historical ecological theory. I begin with a review of accepted definitions for historical ecology and discuss its application in several contexts. Additionally, I have included a review of historical ecological research conducted on the Northern Channel Islands, specifically the application of diachronic, allometric approaches for interpreting human impacts on intertidal resources and the implications of these studies for resource management. I conclude with a discussion of how historical ecology theory has informed my research.

HISTORICAL ECOLOGY First appearing in academic literature in the 1950s, historical ecology was used to discuss the interdisciplinary research taking place between biologists and archaeologists (Nichols 1956; Redman 1999). From these modest beginnings, historical ecology has grown into an interdisciplinary research framework that integrates a wealth of information to explore human-environment relations across time, space, and culture (Balée 1998; Balée and Erickson 2006; Crumley 1994, 2007; Redman 1999). Historical ecology became popularized in archaeology and other disciplines in 1994, after the publication of Carole Crumley’s edited volume Historical Ecology: Cultural Knowledge and Changing Landscapes. This edited

volume focused on the diachronic methods used by anthropologists to understand human- environment relations. Crumley argued that this framework could stimulate interdisciplinary studies between the humanities and sciences. Shortly after the publication of Crumley and colleagues’ work, historical ecology was further explicated by Balée (1998:14) who established four core postulates for the discipline: 1. Nearly all, if not all, of the nonhuman biosphere has been affected by human activity. 2. Human activity does not necessarily result in environmental destruction, nor does it always create a more hospitable environment. 3. Different cultural practices and socioeconomic and political activities can have varying effects on the biosphere. 4. Humans and the environments within which they interact can be regarded as a single phenomenon. Differing from ecology, which tends to focus on time spans of only a few decades or less, historical ecology consults much deeper time scales and suggests that in order to understand and manage modern ecosystems, researchers should seek to identify changes (natural or anthropogenic) within ecosystems through millennia (Braje 2010; Deevey 1964). Since its inception, various applications, definitions, and uses of historical ecology have been suggested (Rick and Lockwood 2013). In its simplest form, historical ecology is defined as the integration of ecology and history (Crumley 1994; Gragson 2005). Balée and Erickson (2006) suggests that, more broadly, historical ecology is the study of interactions through time between societies and the environments in which they live. Additionally, Balée places considerable importance on how these interactions contribute to both past and contemporary cultures and landscapes. Other researchers have defined historical ecology as the use of historical knowledge for the management of ecosystems and the establishment of conservation goals (Egan and Howell 2001; Swetnam et al. 1999). Bürgi and Gimmi (2007) advocate for the use of historical ecology as a tool for establishing reference points for framing management goals. For the purpose of my research, I have relied heavily on the definition provided by Rick and Lockwood (2013:46) who advocate for “a broad definition of historical ecology as the use of historical and prehistoric data (e.g., paleobiological, archaeological, historical) to understand ancient and modern ecosystems, often with the goal of providing context for contemporary conservation.” Historical ecology, then, is a means for

understanding human-environment interactions in the past, and is concerned with understanding natural variations as well as the application of these data for improving modern management goals.

Data Collection and Methods of Historical Ecology Historical ecologists rely on data collected from several academic subfields, including environmental history, conservation archaeobiology, and conservation paleobiology (Rick and Lockwood 2013). Historical data such as catch records, census tracts, ethnohistoric accounts of land use, and historical photographs have been used by several researchers (Martin and Szuter 1999; Szabó and Hédl 2011). Size data from historical fishing accounts, for example, have been particularly important for researchers studying the impacts of overfishing around the world (Finney et al. 2002; McClenachan 2009; McLeod and Leslie 2009). Historical ecological studies of the collapse of the cod industry have consulted historic size data to help formulate conservation agendas (Alexander et al. 2009). Perspectives from anthropology and ethnohistory, including traditional ecological knowledge in the form of ethnographies, have been especially useful in providing insights into how human activities impact and manage ecosystems (Blount and Pitchon 2007; Bürgi and Gimmi 2007; Carothers 2011; Lauer and Aswani 2010; Lepofsky 2009). Paleobiological data, extending from a few decades to millions of years ago, has been especially useful in historical ecology research. Several ecosystems have been studied using these data including freshwater, marine, and terrestrial ecotones. Animal bones, teeth and shells, as well as pollen, phytoliths, and diatoms have been used to reconstruct past environments. On the Northern Channel Islands, researchers have used pollen studies and sediment deposits from several canyons to determine how the biota of these islands has transformed through the Holocene (Anderson et al. 2010). The results of ethnobotanical studies in several regions of the world are also being used to identify areas that may be especially at risk for plant and animal loss as a result of global climate change. Finally, paleoclimate data have been used extensively in historical ecology to disentangle climatic versus anthropogenic driven changes to ecosystem structure. High resolution paleoclimate data from the Santa Barbara basin have been used frequently by researchers conducting human-environmental research on the Channel Islands.

The term conservation archaeobiology was likely first used by Rick and Lockwood (2013) to discuss the third subfield of historical ecology. Although similar to paleobiology in several ways, including the datasets used, a key difference between the two is that archaeological data are generally the result of human activities while paleobiological datasets occur naturally (Rick and Lockwood 2013:48). Archaeobiology uses plant and animal remains, artifacts, genetics, and other data to make informed decisions for conservation and restoration. Braje and colleagues (2015) use such datasets to address black abalone restoration programs currently taking place on the northern and southern Channel Islands. Black abalone have received significant attention after the collapse of populations during the late 20th century. Braje and colleagues suggest that identifying locations where black abalone appear to be relatively abundant in the past can inform research managers of areas that may be well suited for seeding programs to help repopulate the area. Smith (2009) identified alterations of plant and animal communities in the Mississippi River Valley. McGovern and colleagues (2007) identified the impacts of the settlement of Iceland by farmers who introduced several flora and grazing animals to the island and triggered a massive transformation of the ecosystem leading to wide-spread erosion and ecological devastation. Archaeological datasets have also been applied to aquatic ecosystems and organisms, including freshwater mollusks (Unionidae) in Texas (Randklev et al. 2010) and ancient and modern red abalone (Haliotis rufescens) populations in California (Braje et al. 2009). Archaeological datasets are relevant for determining proxies for prehistoric species abundance, natural and anthropogenic landscape alterations, and the long-term formation of ecosystems under human pressure (Dean 2010). Whether taken collectively or separately, these datasets allow historical ecologists to discuss ecological variation on vast temporal and spatial scales and transcend many of the existing challenges facing conservation and resource management today, including the shifting baseline syndrome (Pauly 1995). Historical ecology data and methods are subject to several limitations. The proxy records used by researchers are subject to a number of physical, biological, and cultural processes (Swetnam et al. 1999). Several historical datasets such as climatic records are often limited due to “cultural filtering” (Swetnam et al. 1999). Weather stations during the 18th and 19th centuries were often located in low-elevation areas, near or within settlements, and were often moved from one area to another, causing inconsistencies in the available data.

Additionally, Rick and Lockwood (2013:47) compiled a list of challenges and limitations when using datasets from each of the three aforementioned historical ecology subfields. Paleobiological datasets are often limited by preservation conditions posing challenges for determining the natural systems of the past. Archaeological datasets share similar limitations as described above. Most notably, archaeological datasets are, in many cases, largely human- selected assemblages and are limited by preservation as well as the presence of humans in an area for a sustained length of time. To mitigate these challenges, researchers often use known datasets, such as modern weather data, as references for unknown datasets (Swetnam et al. 1999). The refinement of methodologies and rigorous testing are necessary to identify well- defined proxy records. Despite the constraints and limitations of historical, archaeological, paleobiological, and several other datasets, however, the insights provided by the aforementioned disciplines offer powerful lessons about the past, present and future (see Braje and Rick 2013).

Historical Ecology in Practice Archaeologists have investigated the relationships between humans and the environment since the inception of the discipline (see Trigger 2006). Only recently, however, have archaeologists switched their attention away from how humans have adapted to their environment, to how humans have transformed ecosystems (Redman 1999; Redman et al. 2004). In recent decades, researchers have argued that archaeology and other historical disciplines have the potential to supply a deep historical framework for the investigation of human-environmental interactions over the longue durée. They have emphasized the possibility for these data to inform contemporary management issues, providing a niche for archaeologists within historical ecology theory (Braje and Rick 2013; Fisher and Feinman 2005; Jackson et al. 2001; Kirch et al. 1992: Lyman and Cannon 2004; Redman 1999; Redman et al. 2004; van der Leeuw and Redman 2002). Discussions regarding environmental degradation by human activities are contentious. Ancient peoples have long been viewed as the original conservationists who were able to live sustainably and maintain a balance within their environment (Krech 1999, 2005). This ideology suggests that humans are more or less passive victims of natural environmental change (Braje 2010). Archaeological research suggests, however, that

indigenous peoples played an active role in altering and tending their environments regardless of population density or cultural complexity (Grayson 2001). This was accomplished using a variety of mechanisms including hunting and gathering, fire, agriculture, and the translocation of plants and animals across the planet. When these practices are compared to the devastation caused during the Historic Period such as the marine mammal hunting on the world’s oceans during the mid-1700s and the massive loss of biodiversity over the last century, the strategies used by ancient peoples were of relatively low-impact. Several studies conducted over recent decades suggest that virtually every landscape currently and/or previously occupied by humans has been manipulated in some way. The scale of these impacts varies across both time and space. Historical ecology theory has been applied broadly and to many ecosystems, both marine and terrestrial (Braje et al. 2007; Egan and Howell 2001; Jackson et al. 2001; Lyman 1996; Lyman and Cannon 2004; Steneck et al. 2002). A long term study of the Emeryville Shell Mound on the central California coast highlighted the potential use of archaeology to determine human impacts on shellfish in the area as well as informing conservation policy (Broughton 1994, 1997, 1999, 2002). Similar research has taken place on the Northern Channel Islands and will be discussed in detail later in this chapter. Fitzpatrick and Keegan (2007) have discussed human impacts on and adaptation to Caribbean terrestrial and marine environments spanning 6000 years. They suggest that although prehistoric peoples were certainly transforming their environment it was not until the arrival of Europeans that degradation of the landscape and rapid resource depletion occurred. Understanding the strategies employed by these prehistoric people as well as identifying pre-European ecology in the region may help researchers to build plans for future recovery. Fluctuation in terrestrial and marine resource availability has also been extensively studied (Braje and Delong 2009; Braje and Rick 2011; Erlandson, Ainis, Braje, Jew, McVey, Rick, Vellanoweth, and Watts 2015; Erlandson, Braje, Gill, and Graham 2015; Whitaker and Hilderbrant 2011; Walker et al. 2002) . More recently, anthropogenic fire use in North America has been discussed by researchers who suggest prehistoric peoples used fire as a means of transforming their environment as well as for promoting a more productive biota (e.g., Anderson et al. 2010; Jones and Perry 2012). Additionally, research conducted on the

use of traditional ecological knowledge coupled with archaeological and ethnohistoric data has aided in the planning and management of resources around the world (Aswani and Lauer 2006; Blount and Pitchon 2007). Lepofsky and colleagues (2015), for example, documented how Northwest Coast First Nations peoples managed the productivity of clams and provide an excellent example of how traditional ecological knowledge and archaeology can aid in modern resource management. These studies demonstrate the potential for archaeology, and anthropology more generally, to contribute a wealth of information to better inform long term environmental change and to assist resource managers in the establishment of management policies.

CASE STUDIES FROM THE NORTHERN CHANNEL ISLANDS Islands have long been considered prime research laboratories because of their temporal history and preservation (Kirch 1997; Kirch and Hunt 1997). This is true for the Channel Islands, which have been used by historical ecologists to assess human impacts on the local marine environments (Braje 2010). Three of the Northern Channel Islands are managed by the National Parks Service (NPS), and Santa Cruz Island is managed jointly by the Nature Conservancy and NPS. Both the terrestrial and marine resources of these islands are protected and managed with a series of marine reserves. Over the past two decades, researchers working on the Channel Islands have used archaeological datasets of flora and fauna remains recovered from archaeological shell middens distributed across the islands to offer resource management strategies, including estimating prehistoric species ranges, sizes, and abundances. Numerous studies conducted on the Northern Channel Islands have focused on long- term environmental change using historical ecological methods (e.g., Braje 2010; Braje and Rick 2011; Braje et al. 2009, 2012a, 2012b; Erlandson, Braje, Rick, Jew, Kennett, Dwyer, Ainis, Vellanoweth, and Watts 2011; Erlandson, Ainis, Braje, Jew, McVey, Rick, Vellanoweth, and Watts 2015; Rick 2007). These studies inform a variety of issues including sea mammal hunting, shellfish overharvesting, kelp forest ecology, and the formation of sand dunes (e.g., Erlandson et al. 2004; Erlandson, Rick, Estes, Graham, Braje, and Vellanoweth 2005; Rick et al. 2006). The effects of long-term human harvesting on breeding pinnipeds on

30 the Channel Islands, specifically on the San Miguel Island colonies, have informed resource managers of prehistoric species ranges and relative abundances (Erlandson, Braje, Gill, and Graham 2015; Walker et al. 2002). Using both historical ecology and statistical analysis, Braje and colleagues (2012b:157-178) used allometry to identify size change in rockfishes (genus Sebastes) on the Northern Channel Islands using over 10,000 years of archaeological and historical data. Their research identified a decline in average rockfish size through the prehistoric period, a slight increase during the Spanish period, and an eventual decline through to the present. They identified a 50 mm reduction in average length when the modern data was compared to the late Holocene occupation of the Channel Islands. Shellfish taxa and stable isotope analysis from archaeological shells have been used by researchers to reconstruct ancient environments and climatic conditions throughout the Holocene (Arnold and Tissot 1993; Kennett and Kennett 2000; Sharp 2000). Other research has focused on the exploitation and human impacts on birds on the Northern Channel Islands (Guthrie 1980, 1993, 2005; Jones et al. 2008; Rick 2007). Studies of shellfish populations and allometric variation through time have emphasized the important role of near shore resources during the prehistoric period (Braje 2010; Braje et al. 2007, 2009, 2012a, 2012b, 2015; Erlandson et al. 2008; Erlandson, Braje, Rick, Jew, Kennett, Dwyer, Ainis, Vellanoweth, and Watts 2011; Erlandson, Ainis, Braje, Jew, McVey, Rick, Vellanoweth, and Watts 2015; Erlandson, Braje, Gill, and Graham 2015; Erlandson, Rick, Estes, Graham, Braje, and Vellanoweth 2005; Kennett 2005; Rick 2007; Rick and Erlandson 2008). Research conducted on the Northern Channel Islands suggests that as human populations grew, shellfish harvesting intensified (Arnold 2001; Glassow 1999). This is supported by the density of shellfish remains found in Late Holocene sites relative to those found in Early or Middle Holocene sites. Researchers have used historical ecological methods to discuss the relative abundance and average size of shellfish species including, black and red abalone (Haliotis cracherodii and Haliotis rufescens), owl limpets (Lottia gigantean), California mussels (Mytilus californianus), turban snails (Chlorostoma sp.), sea urchins (Strongylocentrotus sp.), chitons (Cryptochiton sp.), and others (Braje and Rick 2011; Braje et al. 2007, 2009, 2011, 2012a; Erlandson et al. 1999, 2008; Erlandson, Braje, Rick, Jew, Kennett, Dwyer, Ainis, Vellanoweth, and Watts 2011; Erlandson, Ainis, Braje, Jew, McVey, Rick, Vellanoweth, and Watts 2015; Wolff et al. 2007).

An ongoing historical ecology project on the Northern Channel Islands involves the interdisciplinary work of several scholars who have analyzed the trans-Holocene exploitation of California mussels (Braje et al. 2007, 2012a; Erlandson et al. 2008; Jazwa et al. 2012). Shell middens found across these islands provide archaeologists with incredibly large datasets to analyze the extent to which humans may have transformed the ecology of California mussels. Researchers use average mussel shell length through time as a proxy for California mussel health and suggest that a decrease in average shell length is indicative of either anthropogenic or natural influences (Roy et al. 2003). These data, coupled with ethnographic evidence of population densities on the islands as well as high resolution climate data have been used to determine anthropogenic versus natural effects on California mussel populations (Kennett, D.J., J.P. Kennett, J.M. Erlandson, and K.G. Cannariato 2007). California mussels have received specific attention due to their ubiquity in shell middens along the California coastline. In a trans-Holocene study, Braje et al. (2012a) studied 57 components at 31 prehistoric sites from the Northern Channel Islands with occupations ranging from ca. 12,200 to 100 cal BP. They found that California mussels made up over 50% of the assemblages in 35 site components. Additionally, after sampling thousands of whole California mussels recovered from archaeological sites, Braje et al. (2007) determined that anthropogenic over-harvesting caused a significant reduction in average shell length through time. Intense predation of California mussels through time and their use as an ornamental and a technological resource makes studies regarding their use of great importance. By understanding human impacts on this resource in the past, historical ecologists seek to provide a more complete history of California mussel populations on the Northern Channel Islands. Research, however, has been hindered due to taphonomic and natural processes that occur in archaeological sites where California mussels are rarely recovered intact (Claassen 1998). Recognizing the need for a method to estimate total shell length of a California mussel based on the commonly recovered hinge portion, Greg White (1989) created a template to estimate within 1 cm the total shell length using the hinge. Although still in use today (Braje et al. 2007; Jazwa et al. 2012), this method was determined to be statistically unreliable when estimating shell length (Bell 2009). Additional research has been conducted by Campbell (2013) using the common mussel (Mytilus edulis). Rudolph (1990) determined that it was

possible to create a regression formula to estimate the total shell length of a California mussel, but little work has been done to support or deny his claim. More recently, the allometric approach was used by Singh and McKechnie (2015), who recognized that a suitable regression formula for estimating California mussel shell length could be developed lending support to Rudolph’s assumptions (see also McKechnie et al. 2015). In the past, several researchers have chosen to avoid fragmentary shells altogether and instead have only measured whole shells recovered from archaeological sites (see Braje 2010; Erlandson et al. 2008). This, however, is problematic because it may introduce a bias by selecting only those shells that preserve. Thus, my research questions were developed to remedy some of these challenges by identifying a statistically reliable method for estimating total shell length of California mussels from the hinge portion of the shells, commonly recovered from archaeological contexts. Historical ecology and the integration of interdisciplinary datasets offer the critical theoretical framework to address my research questions effectively. My research integrates data collected from shellfish remains from archaeological sites on the Northern Channel Islands, modern California mussel shell length from CINP, a sample of whole mussels from the San Diego area, and sea surface temperature (SST) curves and other paleoclimatic data from the Santa Barbara Basin (Kennett 2005; Kennett and Ingram 1995). Site chronologies were previously established by researchers using radiocarbon dating to determine the estimated occupation age for archaeological sites. In Chapters 5 and 7, California mussel ecology is discussed; however, in each chapter the ecology section focuses on specific aspects of the California mussel that are relevant to the research questions being explored. Therefore, I provide a California mussel ecology overview in the next chapter where these concepts are discussed in greater detail. Additionally, several examples of California mussel procurement and use in the ethnographic record are included.

CHAPTER 4

MYTILUS CALIFORNIANUS

A central component of my research focuses on the importance of California mussels as a prehistoric resource and applies allometric methods to determine if correlations in mussel growth patterns can be identified. Therefore, it is necessary to review the morphology of California mussels. Here, I provide a succinct review of the biology and ecology of California mussels. I begin with a review of their natural history, including the habitat range and several important physical properties that make them distinguishable from other Mytilidae. I have included an inventory of non-human predators, as well as a brief discussion regarding reproduction and growth. I conclude with a review of ethnographic support for the collection of mussels in prehistory.

ECOLOGY California mussels are a sea invertebrate distributed from the Aleutian Islands to the Socorro Islands, Mexico, on the Pacific Coast of North America (Suchanek 1981). The habitat range for these bivalves extends between –30 m to +4 m (Chan 1973), but they are found in highest densities within the middle intertidal zone (Paine 1974). In rocky shore habitats, California mussels often dominate intertidal communities despite their relatively narrow niche. California mussels are distinguishable from other mussel species found within its habitat range by their coarser and sturdier shell (Jones and Richman 1995). Additionally, California mussels have more prominent radiating ridges and distinctive concentric growth lines (Gosling 1992). The largest California mussel ever recorded was >266 mm (Suchanek 1986); however, studies in southern California rarely identify mussels that exceed 180 mm (Jones and Richman 1995).

Diet, Reproduction, and Growth California mussels obtain food by secreting mucus over their gills. In a process referred to as mucus feeding, mussels draw in microorganisms and detritus to their mantle cavity via ciliary currents (Jones and Richman 1995). Organisms consumed by California mussels include dinoflagellates, organic particles, small diatoms, zoospores, various unicellular algae, protozoa and detritus. Coe and Fox (1942) determined that the density of dinoflagellates in the water have a direct correlation to mussel growth. California mussels reach maturity at 15 mm, although they may not reproduce at this point (Jones and Richman 1995; Schmidt 1999). Coe and Fox (1942) estimated that first spawning may take place after reaching 70 mm. California mussels spawn continually throughout the year, although the amount of gametes released are quite low outside of spring and fall months (Seed and Suchanek 1992; Yamada and Dunham 1989; Young 1946). Spawning takes place outside of the body, with both the female and male discharging eggs and sperm respectively, through the excurrent chamber (Widdows 1991). Eggs are then fertilized in open water and the probability of fertilization is short due to the three to four hour lifespan of the gametes (Lutz and Kennish 1992; White 1937). Temperature and food supply are particularly important factors for reproduction. The success of larvae is dependent on several factors including suitable environmental conditions, adequate food supply, the presence of predators, and the availability of suitable substrata for settlement (Seed and Suchanek 1992). Growth is variable in California mussels and can be influenced by sex, age, size, and environmental conditions (Seed 1976; Seed and Suchanek 1992; Yamada and Dunham 1989). Growth is most rapid in individuals under three years of age, specifically during the third month of age when body size increases by two-thirds (Seed and Suchanek 1992). After this period, growth rate slows rapidly. Although several factors influence growth, water temperature is perhaps the most important growth-controlling factor. During months when the temperature is highest, there is a marked decrease in growth. The optimal temperature for growth is between 15 and 19°C, with a sharp decrease in growth occurring in waters above 20°C. Additionally, mortality increases by 89 to 100 percent in waters reaching 25°C. This has strong implications for mussel populations as SST continues to increase and longer durations of unseasonably warm water lingers in the Pacific Ocean.

Growth is also influenced by wave action. Mussels exposed to heavy surf grow more slowly and have thicker shells than those living in more sheltered environments. During winter months when storms are more common, growth can be interrupted. Mussels smaller than 20 mm are not generally found 18 m below the surface, indicating that larva recruitment may take place closer to the shallow portions of the bed (Paine 1976a). Several biologists have found that mussels at higher positons in the intertidal experience slower growth rates (Dittman and Robles 1991; Kopp 1979; Seed and Suchanek 1992; Suchanek 1985). The lifespan of California mussels is not known, though it is possible that some individuals may live between 50 and 100 years in suitable conditions (Jones and Richman 1995).

Table 3. Common Predators of California Mussels Common Names Type Scientific Name Sea Star Invertebrate Pisaster ochraceus Crab Shellfish Pugettia product Sea Otter Sea mammal Enhydra lutris White-winged scoter Bird Melanitta deglandi Surf Scoter Bird Melanitta perspicillata Black Scoter Bird Melanitta nigra Dogwhelk Bird Nucella lapillus Spiny Lobster Shellfish Panulirus interruptus Barrow's Goldeneye Bird Bucephala islandica Source: Jones and Richman 1995.

Competitors and Predators The California mussel is the dominant competitor over both bay mussels (Mytilus trossulus) and barnacles (Cirripedia). In areas where sea palm (Postelsia palmaeformis) is present, however, the distribution of California mussel is negatively impacted (Seed and Suchanek 1992). Additionally, many non-human predators exploit the California mussel (Table 3). Lutz (1980) identified an 80 percent attrition rate among some California mussel populations as a result of water fowl predation. Sea stars (Pisaster ochraceus) also predate heavily on California mussels consuming up to 80 mussels per year (Feder 1970). They generally will not eat mussels that exceed 100 mm in length and tend to eat smaller individuals (Paine 1976b). Interestingly, when sea stars are removed from a system, the habitat range of California mussel increases in depth and recedes when the sea star returns.

Although, sea otters (Enhydra lutris) are known to consume California mussels, the extent of this behavior is not well known (Jones and Richman 1995). In addition to predation, storm events also contribute to mortality among Mytilus populations (Suchanek 1985).

Ecological Succession After a mussel bed is cleared, either by anthropogenic or natural activity, it takes a minimum of two and a half years to re-establish (Jones and Richman 1995), but can take between 5 and 100 years. California mussels tend to recolonize areas where extant mussel populations are present or byssal threads from previous colonies still exists (Petersen 1984). Depending on the environmental conditions, it can take anywhere from eight to thirty-five years for a mussel bed to return to its previous condition (Yamada and Peters 1988). The larvae’s preference for colonizing areas where mussel beds are well established may be related to the slow recovery of areas where mussel beds have been cleared (Bell 2009). The slow recovery of mussel beds and the long-term harvest of California mussels on the Channel Islands suggest that the Chumash may have developed a form of sustainable aquaculture.

ETHNOGRAPHIC EVIDENCE FOR THE HARVESTING OF MUSSELS Accounts of shellfish procurement by hand exist for several cultures around the world (Waselkov 1987). Ethnographic accounts from the western coast of North America often describe the gathering of shellfish to have been commonly done by women, children, and the elderly although there is some indication that men actively participated as well (Greengo 1948; Kroeber and Barrett 1960). Mussels were often boiled or roasted, although some accounts suggest they may have been dried to keep from spoiling and rehydrated prior to consumption (Gifford 1939). Bay mussels are commonly believed to have been easier to collect by hand than sea mussels (Greengo 1948). Hudson and Blackburn (1985:253) identified pry bars as a means by which shellfish may have been easily removed from rocks. Tartaglia (1976) suggested that shellfish was primarily gathered during the winter months to help provide during periods of resource scarcity. Size preference and harvesting strategies have also been debated across space and time. In a thorough study of shellfish collection in Australia, the Anbara would tear off mussels in chunks, then rinse the load and clean them of barnacles. They would then discard

37 the smaller mussels and only retain the larger ones (Meehan 1982). A similar preference for larger shellfish was noted by Lasiak (1992) who studied shellfish procurement amongst groups living in South Africa. Although ethnographic accounts for the harvesting of California mussels by the Chumash do not exist, some have debated whether they employed the “stripping” or “plucking” method when collecting. The stripping strategy involves the removal of an entire mussel bed en masse while the plucking strategy involves the selective harvest of larger mussels (Jones and Richman 1995). In California, researchers have used shell length distribution data for mussels recovered from archaeological contexts to infer which strategies may have been in place (Bouey and Basgall 1991; White 1989). The results of their studies have been contested, however, due to issues with sampling strategies (Jones and Richman 1995). Jones and Richman (1995) argued that without a method for estimating total shell lengths from mussel shell fragments in archaeological assemblages, inferences about ancient collection strategies remain dubious. By incorporating a method for estimating total shell length of a mussel from hinge fragments with whole shell measurements, one could obtain a more reliable dataset for determining which collection strategies may have been used. The regional distribution and ease of collection made California mussels a prime target for human use in the prehistoric past. California mussels were not only used for subsistence, but the shells were often used to create shell beads and fishhooks (Hudson and Blackburn 1985). The importance of California mussels as a resource for prehistoric peoples only further solidifies the need for more stringent methods and historical ecological studies of the possible anthropogenic influence on this species. In the next chapter, I present the results of a methodological study in which I use an allometric approach to identify a method for estimating the total shell length of a California mussel from measurements taken from attributes found on the hinge portion of the shell.

CHAPTER 5

ESTIMATING CALIFORNIA MUSSEL (MYTILUS CALIFORNIANUS) SIZE FROM HINGE FRAGMENTS: A METHODOLOGICAL APPLICATION IN HISTORICAL ECOLOGY

This chapter was published in the Journal of Archaeological Science in 2015.

INTRODUCTION In recent decades, interest has grown in the application of archaeological data to modern environmental issues in order to enhance our understanding of the consequences of human decision-making through time (e.g., Balée and Erikson 2006; Butzer 1982; Crumley 1994; Fitzpatrick and Keegan 2007; Johnson et al. 2005; Kirch 1982; Lepofsky 2009; Lyman 2006; Redman 1999, 2005; Rick and Erlandson 2008; Rick and Lockwood 2013; Swetnam et al. 1999; Wolverton and Lyman 2012). Archaeological shellfish sizes have become an important method for reconstructing past environments and assessing human impacts on near shore ecosystems (e.g., Bailey and Milner 2008; Campbell 2008; de Boer et al. 2000; Erlandson, Braje, Rick, Jew, Kennett, Dwyer, Ainis, Vellanoweth, and Watts 2011; Faulkner 2009; Giovas et al. 2010, 2013; Jerardino 1997, 2010; Lasiak 1991; Mannino and Thomas 2001; Milner et al. 2007; Morrison and Cochrane 2008; Morrison and Hunt 2007; Stager and Chen 1996; Stiner et al. 1999), harvesting strategies (e.g., Alvarez-Fernàndez et al. 2011; Jones and Richman 1995; Whitaker 2008), and mobility patterns (e.g., Allen 2012; Mannino and Thomas 2002). Heavy predation by humans and other large predators, as well as climatic variation including fluctuations in sea surface temperatures, can reduce the mean shell sizes of many shellfish populations. Reduction in resource availability can result in the innovation of new technologies to procure previously unattainable resources and changes in diet and

foraging strategies, making shellfish size fluctuations an important component of understanding past human behavior. Changes in California mussel (Mytilus californianus) shell length through time have been a particularly important proxy for natural fluctuations and anthropogenic impacts on near shore intertidal communities on North America’s Pacific Coast (Braje 2010; Braje et al. 2007, 2012a; Erlandson et al. 2008; Jazwa et al. 2012; Rick 2007). Archaeologists are often limited, however, by taphonomic processes that cause California mussel shells to fragment (see Claassen 1998). Two primary methods have been employed to deal with this issue. First, some studies, particularly in locations and at sites with excellent preservation, have focused on the measurement of whole shells (Braje 2010; Erlandson et al. 2008; Rick 2007). When large samples from well-preserved deposits are not available, archaeologists have employed a template to estimate whole shell length using the hinge portion of California mussel shells (e.g., Braje et al. 2007; Jazwa et al. 2012; White 1989). This template allows the researcher to group mussels into size classes with 1 cm variation using the visual inspection of the mussel hinge and comparison to a template derived from modern mussel shells. Recent experimental work, however, has shown this technique to be statistically unreliable (Bell 2009) and not replicable from one trained analyst to another (T. Rick, personal communication 2013). The lack of reliable methods to calculate whole mussel shell length from fragmented specimens has created the need for new techniques to estimate total shell length of California mussels from hinge fragments.

Figure 3. Watercolor of a Mytilus californianus shell with labels of several of the physiological features mentioned in the text.

Researchers have attempted to develop new methodologies for evaluating mussel shell length fluctuations through time (Campbell 2013; Rudolph 1990). Rudolph (1990) believed that correlations could be identified between the hinge portion of a California mussel and the total shell length. He used a sample of whole archaeological mussels and created a regression formula measuring the width of a California mussel hinge approximately 1.0 cm from the umbo beak, the rounded protuberance located at the extreme anterior end of the shell (Figure 3). He determined that a regression formula with a statistically reliable r- squared value could be identified, however, his method was never fully explored. Campbell (2013) used a software application to predict blue mussel (Mytilus edulis) size using dimensions of their archaeological remains that accounts for allometric growth. Over half of the shell must be recovered, however, to conduct these measurements and it is often difficult to determine if the hinge portion recovered from an archaeological context is in fact at least half of the original shell. This method also is problematic because access to the software is limited and field measurements are impractical. For our study, we employed the regression, or allometric, approach to estimate the length of California mussel shells from hinge fragments (Reitz and Wing 1999:70). Using modern samples collected from San Diego, California, we developed a series of regression formulae based on three measurements of the hinge portion of a California mussel shell that

can accurately predict shell length to within 1.0 cm. The reliability and merits of these techniques were tested using both an archaeological and a modern sample. We identify one hinge measurement, in particular, that is statistically reliable, replicable, easy to record, and applicable in both field and laboratory settings. This allometric technique will enable researchers to measure ecological change in California mussel populations through time; recovering previously unattainable data that can be directly applied to the management of modern and future California mussel populations.

BACKGROUND California mussels are found in the mid-intertidal zone along the New World Pacific Coast from the Aleutian Islands, Alaska, in the north to the Socorro Islands, Mexico, in the south (Jones and Richman 1995). Concentrated in dense clusters of up to 1000 individuals, California mussels range in average shell length from about 30 to 180 mm and can be easily collected and processed with very little technology (Coe and Fox 1942; Jones and Richman 1995). Mussels found in southern California tend to be smaller than those living north of Puget Sound where they may reach lengths of more than 240 mm (Coe and Fox 1942). California mussel growth is highly dependent on environmental conditions. Coe and Fox (1942) completed the first comprehensive study of California mussel growth and determined that tidal height, food availability, water temperature, sex, wave action, and age influenced growth rates. For example, because mussels only feed when submerged, there exists a relationship between tidal depth and growth rate and pattern, with length decreasing with tidal height (Jones and Richman 1995). Additionally, mussels exposed to heavy surf experience slower growth and increased shell thickness when compared to mussels that live in less exposed environments. The largest California mussel on record measured > 266 mm (Suchanek 1986), but adult individuals tend to be much smaller than this on average. In an experiment with southern Californian mussels, Coe and Fox (1942) found that growth was rapid in the first year of a mussel’s life, with individuals reaching lengths of 51 mm. Growth rates remain high over the next two years with individuals reaching average lengths of 80 mm in year two and 91 mm in year three, but growth rates slow considerably thereafter. In their study of nearly 10,000 years of human impacts on California mussels recovered from

archaeological sites on San Miguel Island, California, Erlandson et al. (2008) found that only 2% of over 9800 whole mussels exceeded 90 mm in length. California mussels feed on a variety of small organisms by secreting a thin layer of mucus over their gills and collecting particles from the water, these are then sorted and the desired particles are strung into the mouth (Coe and Fox 1942; MacGinitie 1941). California mussel reproduction occurs when eggs and sperm are released through the excurrent chamber. The spawning period for California mussels is debated (Coe and Fox 1942; Jones and Richman 1995; Shaw 1988; Suchanek 1981; Young 1942, 1946), but temperature and food supply are considered to be particularly important factors for controlling reproduction (Jones and Richman 1995). Due to their concentration in the intertidal zone, California mussels are especially vulnerable to predation during low tides. In addition to human harvesting, this includes predation by a variety of waterfowl including the white-winged scoter (Melanitta deglandi) and other diving ducks. California mussels also are the preferred prey of the common sea star (Pisaster ochraceus) (Jones and Richman 1995; Lutz 1980). There are some limitations regarding the size of a mussel that a sea star is able to consume, however, and generally sea stars will not predate upon mussels that exceed 100 mm in length. In some instances, sea otters (Enhydra lutris) have been known to prey on mussels but only after their preferred foods are depleted from their foraging range (Ebert 1968). Increased tidal exposure can reduce predation pressure on California mussels by other marine species, but exposure above average sea level limits a mussel’s ability to feed which can inhibit growth and spawning (Bayne et al. 1975). Additionally, increased exposure raises the likelihood of anthropogenic harvesting and bed destruction from recreational activities (Smith et al. 2008). When a mussel bed is cleared, either by natural changes or anthropogenic impacts, it takes a minimum of two and a half years to start the regeneration process (Jones and Richman 1995). Once mussels begin to repopulate an area it typically takes between 8 and 35 years to return to its pre-disturbance state. Suchanek (1979) has suggested, however, this process, which is highly sensitive to environmental conditions, can take up to 100 years. Once repopulated, a relatively undisturbed population can survive for 50 to 100 years (Suchanek 1981).

Figure 4. Location map of the Santa Barbara Channel region, the Northern Channel Islands, San Miguel Island, and CA-SMI-232.

California mussels have been an important food and tool source for ancient and historical occupants of the North American Pacific Coast for at least 12,000 years (e.g., Erlandson, Rick, Braje, Casperson, Culleton, Fulfrost, Garcia, Guthrie, Jew, Kennett, Moss, Reeder, Skinner, Watts, and Willis 2011). On the Northern Channel Islands (Figure 4), located between 20 and 44 km from the mainland coast of California, data from archaeological sites have long been used to explore the relationship between humans and intertidal shellfish communities (e.g., Braje et al. 2007, 2012; Erlandson et al. 2008; Erlandson, Braje, Rick, Jew, Kennett, Dwyer, Ainis, Vellanoweth, and Watts 2011; Jazwa et al. 2012). Due to the ease of collection en masse as well as their extensive distribution around the islands, Braje et al. (2007:740) ranked California mussels as the top prey choice for marine foragers living on the Channel Islands. Today, California mussel harvesting is mostly recreational; a ten pound (in shell) collection limit requiring a one-day fishing license is the only legislation regarding the harvest of mussels outside of marine protected areas.

MATERIALS AND METHODS In November 2012, Campbell collected a robust sample of modern California mussels (n = 135) from a single rocky intertidal habitat in San Diego, California. Prior to collection,

44 arbitrary classes were established to ensure adequate total shell length variation during the collection process: Class 1 (n = 55, 0-38 mm), Class 2 (n = 50, 38.1-68 mm), and Class 3 (n = 30, 68.1-86.32 mm). Each mussel was measured and classified in the field, and transported to San Diego State University’s Environmental Anthropology and Archaeology Laboratory for further analysis. The viscera of each mussel were discarded and broken mussel shells were removed from the sample. Each valve was placed in exterior view with the umbo located at the distal end, the placement of the hinge (either on the left or right side of the shell) was used to determine the left from the right valve. The total length of the right and left bivalves of each mussel was measured with digital calipers, recorded, and shells were cataloged and stored. The right valve of each mussel was used to record three different hinge measurements: umbo-width, umbo-length, and umbo-height. Umbo-width was measured where the hinge plate is at its greatest width. Umbo-length was recorded by measuring from the tip of the beak to the interior end of the hinge plate. Umbo-height was measured 5 mm from the tip of the beak and the calipers were placed with the teeth perpendicular to the shell (see inset photographs in Figure 5). Each measurement was recorded three times and the results were averaged. We then employed a regression method to build formulae that can predict whole California mussel shell length from hinge measurements. The regression approach provides an accurate method for estimating the shell length from fragments and involves the determination of the relationship between two variables, commonly accomplished using the least-squares regression method (Johnson and Bhattacharyya 1992). For two variables under consideration, x and y are plotted against one another and the least-squares method determines “the equation for the line that minimizes the sum of squares of the vertical distances from the data points to the regression line” (Orchard 2001:67, also see Casteel 1976; Ricker 1973). Common for estimating whole shell length, the linear or exponential relationship is expressed with a mathematical formula that describes the relationship between the two variables being compared. In Microsoft Excel, regression formulae were built using the averaged measurements to determine correlations in total mussel shell length and umbo measurements. The umbo-width, -length, and -height measurements were assigned the x- variable; total mussel shell length was assigned the y-variable for each equation.

Two tests were conducted to determine the validity of the regression formulae. First, a sub-sample of the modern mussels (n = 30) used to generate the regression formulae were selected by the authors with 10 mussels being chosen randomly from each of the previously established shell classes to ensure a variation in shell length. Using a hammer, the mussels were broken, leaving only the hinge portions intact. A graduate student was trained to measure umbo -width, umbo-length, and umbo-height using a sample of whole mussel shells and then instructed to record these measurements on the fragmented mussels, repeating the measurement three times. The results were averaged, applied to the respective regression formulae, and total shell length for each mussel was estimated. The student was also asked to rank each method based on the speed and ease of data collection. A one-way analysis of variance (ANOVA), a procedure that analyzes whether the differences between more than two groups are statistically meaningful (Sokal and Rohlf 1981), was used to determine whether or not whole shell measurements and the three different hinge measurements produced significantly different results. Since mussel shell growth is not consistent throughout the organism’s lifetime and has been shown to slow after three years, we examined the assumptions of testing a linear relationship between total shell length and umbo measurements using P-P plots of regression standardized residuals. P-P plots check for normal distribution of data and help determine whether data is curvilinear, skewed, or should be transformed.

Figure 5. Regression plot and the derived regression formula for California mussel shell length versus umbo-width, umbo-length, and umbo-height. Insets: Photographs demonstrating how to measure California mussel umbo-width, umbo-length, and umbo-height.

Figure 6. A) Normal P-P plot of regression standardized residuals of mean shell length. Scatterplots of standardized residuals plotted against standardized predicted values of total shell length using B) umbo-width, C) umbo-length, and D) umbo-height.

A random sample (n = 30) of whole California mussels excavated from an archaeological site on San Miguel Island, CA-SMI-232, was used to test the reliability of the regression formulae when applied to mussels from archaeological contexts (for details on CA-SMI-232 see Braje 2010). Using digital calipers, the same trained graduate student measured umbo width, length, and height, following procedures described above. The student compiled the data and the measurements were used to calculate total shell length for each mussel using the individual formulae. The estimated total shell length was then compared to the known shell length using a one-way ANOVA.

RESULTS As seen in Figure 5, most of the hinge measurements from our modern mussel sample (n = 135) were well correlated to total shell length. Our analysis produced a regression formula for umbo-width as y = 8.2026x + 1.5967; for umbo-length as y = 16.443x + 7.7068; and for umbo-height as y = 12.269x – 28.513. Umbo-width showed the strongest relationship with total shell length (r-squared = 0.930, p < 0.05), umbo-length the second strongest (r- squared = 0.893, p < 0.05), and umbo-height showed the weakest relationship (r-squared = 0.771, p < 0.05). Results of our P-P plots indicate that our data are normally distributed for all three measurements with only minimal outliers (> 2 or < -2) in the umbo-length and height samples, suggesting that curvilinearity and non-constant variance are not a concern and the data meet the assumption for parametric analysis (Figure 6). Based on a subsample (n = 30) of modern mussels shells, we then tested the reliability of each regression formula. Comparing the mean shell length from each sample, each of the three umbo measurements predicted the mean shell length to within 1.0 cm (Table 4). In a sample, individual variation is expected but our analysis describes the aggregate data for the group. By this measure, umbo-height was the most accurate predictor at less than 1 mm difference, while umbo-width was the least accurate at 9 mm difference. Our one-way ANOVA analysis produced no statistically significant differences (F = 0.386, df = 3, 116) between mussel shell length derived from whole shell measurements or any of the three regression formulae using umbo measurements. The trained graduate student performing the test indicated that the umbo-length measurement was the fastest and easiest measurement to collect followed by the umbo-width and umbo-height respectively. In order to validate our regression formulae for archaeological mussels, we used a subsample of excavated whole California mussel shells from CA-SMI-232. On average, the total length of these 30 mussels was predicted within 1.0 cm by both umbo-width and umbo- length measurements. Mean shell length from umbo-height measurements was more than 1.5 cm different than the known whole shell length. A one-way ANOVA analysis produced statistically significant differences (F = 15.37, df = 3, 116) between the methods. A Tukey Post Hoc test, to see where these differences lay, revealed that umbo-height was significantly different (p < 0.05) from known total shell length, umbo-width, and umbo-length

Table 4. California Mussel Shell Sizes (TL) Used in our Study from Both Modern and Archaeological Samples, Derived from Whole Shell Measurements and Regression Formula Predictions Based on Umbo Measurements. The Mean Shell Length and Standard Deviations are Reported for Each Category.

Modern Mussels CA-SMI-232 Mussels TL from TL from TL from TL from TL from TL from Umbo Umbo Umbo Umbo Umbo Umbo TL Width Length Height TL Width Length Height Sample 1 36.0 40.6 31.3 22.8 40.5 40.6 44.0 28.5 Sample 2 34.9 41.1 34.0 34.9 40.2 41.1 51.3 26.2 Sample 3 33.7 45.7 40.0 34.5 44.6 45.7 48.5 33.9 Sample 4 27.7 56.2 27.5 28.5 49.8 56.2 41.3 43.0 Sample 5 37.1 38.5 34.6 39.0 39.5 38.5 47.7 22.4 Sample 6 25.1 46.7 24.0 38.2 44.9 46.7 64.2 28.9 Sample 7 27.7 30.9 31.9 27.0 32.1 30.9 41.3 16.1 Sample 8 39.7 17.3 40.4 32.9 16.6 17.3 23.4 2.7 Sample 9 23.4 35.5 23.1 22.6 46.4 35.5 44.9 24.1 Sample 10 32.9 44.0 33.8 45.6 49.3 44.0 49.7 24.2 Sample 11 38.3 31.5 42.4 40.4 31.0 31.5 44.0 12.9 Sample 12 55.4 61.3 52.6 48.2 65.1 61.3 45.2 44.0 Sample 13 39.9 51.6 41.1 58.8 52.0 51.6 58.3 33.5 Sample 14 55.3 45.5 59.8 50.9 51.4 45.5 52.6 33.9 Sample 15 41.4 54.6 43.1 31.0 59.6 54.6 47.4 29.4 Sample 16 45.9 41.8 48.2 42.0 55.4 41.8 49.1 28.7 Sample 17 65.8 30.2 67.4 69.1 26.2 30.2 43.0 12.5 Sample 18 54.1 33.8 53.2 47.3 33.7 33.8 44.4 13.2 Sample 19 58.9 36.8 56.7 77.3 43.2 36.8 48.5 17.7 Sample 20 39.9 13.3 33.2 39.7 11.5 13.3 20.5 -3.0 Sample 21 82.5 44.2 76.4 73.2 45.8 44.2 80.9 34.8 Sample 22 70.1 33.9 57.7 55.3 34.0 33.9 50.2 19.3 Sample 23 74.6 42.3 66.7 62.7 40.8 42.3 68.7 36.3 Sample 24 80.9 48.5 68.5 76.1 55.0 48.5 45.9 50.1 Sample 25 74.5 40.6 68.4 74.1 38.7 40.6 42.3 30.3 Sample 26 69.6 66.7 63.9 82.7 59.4 66.7 48.4 37.5 Sample 27 69.1 38.0 64.9 75.4 45.5 38.0 43.3 31.8 Sample 28 80.6 64.4 83.1 63.6 68.7 64.4 68.1 47.6 Sample 29 71.2 70.1 65.3 74.5 81.6 70.1 88.2 37.4 Sample 30 69.1 38.3 56.9 80.9 31.0 38.3 46.0 19.9 Mean 51.8 42.8 49.7 51.6 44.4 42.8 49.7 27.3 Std dev 19.0 12.9 16.6 19.2 14.7 12.9 13.7 12.5 Note: all measurements are reported as millimeter (mm).

measurements. There is no difference, however, between known shell length, umbo-width, and umbo-length.

DISCUSSIONS AND CONCLUSIONS Archaeologists have long recognized the need for statistically reliable methods for estimating total shell length from fragmented California mussels recovered in archaeological contexts. Our analysis suggests that a regression formula built from two umbo measurements of mussel hinge fragments can reliably predict whole mussel shell length. Umbo-width and umbo-length measurements proved statistically reliable and can predict the mean shell length to within 1.0 cm in robust archaeological samples. Umbo height, while reliable with modern samples, proved statistically unreliable for archaeological samples. This disparity likely resulted from the multiple step process required for calculating umbo-height. A zooarchaeologist must first measure 5 mm from the beak and then shell height is measured from this point. If taphonomic processes have eroded the beak and body of the shell, even small reductions are doubly compounded and can introduce significant measurement errors. Umbo-width and umbo-length measurements, on the other hand, only require one measurement step and, thus, probably reduce the number of errors resulting from shell diagenesis and other taphonomic processes. While both umbo-width and umbo-length proved reliable for modern and archaeological samples, umbo-length (like umbo-height) measurements were susceptible to some important preservation issues. During our laboratory analysis, we noticed that any slight damage to or visible erosion of the mussel beak could result in major discrepancies in the predicted total shell length. The beak of a mussel is the closest point of contact between the shell and the rocky intertidal substrate they cling to via byssal threads. Harvesting can commonly result in slight fractures or clips in the mussel beak, limiting the usefulness of umbo-length as a reliable method for estimating total shell length. In addition, when mussel beds are overcrowded, the beak of individual mussels can become pinched and malformed, making total length predictions from these individuals unreliable (Fox and Coe 1943). The umbo-width method is taken at a more robust, thickened portion of the shell that may be less susceptible to these issues. Although slightly more time consuming and requiring a higher level of precision during the data collection process, measurement of the umbo-width is the

most reliable method for determining total shell length. Because many conditions impact the growth and distribution of California mussels across time and space (Coe and Fox 1942), additional data collection and testing of regression formulae should continue and may help account for variations based on temporal or geographic differences. We also suggest caution when calculating total mussel length from hinge fragments from individual mussels over approximately 90 mm. These individuals are likely three or more years old (Coe and Fox 1942) and their growth rates have likely slowed. In such cases, regression data may need to be log-transformed to correct for issues of curvilinearity and heteroscedasticity. Since previous studies using measurements of whole mussel shells suggest that very few mussels over 90 mm were harvested prehistorically from the Northern Channel Islands (see Erlandson et al., 2008), our sample included only mussels less than 90 mm. Until recently, California mussel populations have been viewed as relatively stable and of low priority for monitoring and restoration, especially compared to other shellfish species such as commercially fished sea urchins (Strongylocentrotus spp.) and protected abalones (Haliotis spp.). In 2014, however, Channel Islands National Park (CINP) biologists began systematically compiling size and coverage data for California mussels at several locations around the Northern Channel Islands as part of their monitoring protocol for rocky intertidal resources (S. Whitaker, personal communication 2013). CINP has recognized the need for increased monitoring as anthropogenic climate change and impacts have altered marine ecosystems, warmed our oceans, and introduced new threats such as ocean acidification. While these data can be used to track future changes, there are no points of comparison and little information on the health and structure of contemporary mussel populations compared with those of the past. While shells recovered from archaeological contexts do not directly reflect the overall size composition of a living shell bed due to human selectivity and harvesting strategies (see Whitaker 2008), our method for estimating total shell length from umbo-width measurements offers a new methodology for building a deep historical record of mean California mussel shell length through time. Hinge measurements can be gathered from a variety of Channel Island sites across time and space and compared against modern shell length as a proxy for the health and structure of California mussel beds.

On the California mainland, the State Water Resource Control Board initiated the State Mussel Watch (SMW) program in 1977, which monitors long-term trends of pollutant concentrations in marine organisms at 71 locations along the California coast (Phillips 1988). This program is intended to monitor trace metals for water quality purposes, but does not collect information on the current state of California mussel populations. The infrastructure for conducting long-term spatial analysis and monitoring of California mussel populations outside of Channel Islands National Park is already in place, then, and modern mussel length measurements could be included as part of the annual study conducted by the SMW. These data could then be compared against mussel length from adjacent archaeological sites using umbo-width measurements. Very quickly, a set of deep historical data would be available to assess the health and structure of modern California mussel beds across the state. Ultimately, our study offers an excellent opportunity to incorporate deep historical perspectives in modern marine management programs (Dayton et al. 1998; Jackson et al. 2001; Pauly 1995; Pauly et al. 1998; Rick and Erlandson 2008; Tegner and Dayton 2000). Using archaeological data to decipher the deeper ecological histories of specific areas and fisheries can provide valuable information regarding the structure of near shore ecosystems in the distant past as well as the processes involved in the creation of anthropogenic land and seascapes during the Anthropocene. Building effective management and restoration plans requires information about historical and ancient harvests and the establishment of reference points or baselines that account for overfishing, other anthropogenic disturbances, and natural climatic fluctuations.

CHAPTER 6

FROM METHODS TO APPLICATIONS

The results of the previous chapter identified a new statistically reliable method for estimating the total shell length of California mussels from the commonly found hinge portion of the shell. The physical elements used to identify if correlations did exist were selected at random and all the measurements were conducted in a laboratory setting. The umbo-width regression formula was determined to have the highest r-squared value (0.9302). When tested using a sample of modern and archaeological mussels, the umbo-width regression formula had the greatest accuracy to within 1 cm of the known length. These results led me to select the umbo-width measurement method for the second phase of my research. In Chapter 7, I apply the umbo-width method to archaeological assemblages along the Northern Channel Islands to collect shell length data from highly fragmented shells; data that were previously unattainable due to taphonomic issues. Using previously recorded site data provided by the Central Coastal Information Center, I identified 16 archaeological sites of known age located on San Miguel, Santa Rosa, and Santa Cruz islands to sample for the application phase of my research. These sites were selected based on their proximity to intertidal locations currently being monitored by NPS as part of their bi-annual monitoring program, additionally, the sites selected for this study were known to have California mussels as part of the artifact assemblage and had been previously radiocarbon dated. Due to access issues and field expenses, samples from San Miguel Island were selected from archaeological assemblages currently housed at the Environmental Anthropology and Archaeology Laboratory (EAAL) at San Diego State University. This limited my ability to sample from sites near monitoring locations. Two sites for Santa Rosa were measured using previously excavated materials curated at the Santa Barbara Natural History Museum. Data for the remaining nine sites were collected over three field visits, two to Santa Cruz Island and one to Santa Rosa Island. The measuring strategy for these sites

involved the identification of a single occupation component, often from an eroded cliff face, and scouring the deposits to measure all visible mussel hinges. Although my goal was to attain, at minimum, 100 measurements per site, this was not always possible. Of the 16 archaeological sites I sampled, seven have less than 100 mussel measurements. Methods for measurement followed guidelines established in the previous chapter; each shell was measured three times and when possible total length was recorded. These data were then compiled in an Excel spreadsheet. My methods, results, and conclusions for this study are reported in the following chapter.

CHAPTER 7

TRANS-HOLOCENE HUMAN IMPACTS ON CALIFORNIA MUSSELS (MYTILUS CALIFORNIANUS): HISTORICAL ECOLOGICAL MANAGEMENT IMPLICATIONS FROM THE NORTHERN CHANNEL ISLANDS

INTRODUCTION Global fisheries and marine ecosystems around the world have been heavily exploited and altered by the actions of humans, resulting in calls to rethink how we manage aquatic resources (e.g., U.S. Commission on Ocean Policy 2004). Decades of overfishing, degradation of marine ecosystems, and global declines in marine biodiversity have spurred scientists, resource managers, and conservationists to explore new methods and interdisciplinary approaches to inform marine management policy and conservation agendas (e.g. Jackson et al. 2001; Myers & Worm 2003; Pauly et al. 1998; U.S. Commission on Ocean Policy 2004). One of the most significant challenges to conservation and restoration biology efforts has been the “shifting baseline syndrome” (Pauly 1995), where restoration efforts have relied on baseline data collected after marine ecosystems have already been degraded by human actions and overexploitation. In 1995, Pauly defined the shifting baselines syndrome and discussed the inherent flaws associated with using relatively modern data for establishing marine restoration targets. Pauly (1995) argued that every new generation of fisheries scientists tends to use catch, size, and abundance data from their early careers to measure the success of modern conservation efforts and the health of marine systems. This has resulted in the gradual degradation of marine ecosystems and global fisheries and a slow-moving ecological disaster, despite our best efforts at conservation and management. One solution for mitigating the shifting baselines syndrome is to extend the

time depth of our management perspectives by using perspectives from archaeology, paleobiology, and history. This approach, known as historical ecology, can offer crucial insights into the changing seascapes of near shore ecosystems and fisheries and help establish baselines that predate the modern collapse of the world’s oceans (Crumley 1994; Erlandson and Rick 2010; Rick and Erlandson 2008; Rick and Lockwood 2013). It has only been relatively recently, however, that archaeologists have come to recognize and appreciate the deep antiquity of human exploitation of marine resources (Bailey 2004; Claassen 1998; Erlandson 2001; Marean et al. 2007; Stewart 1994). Archaeological evidence suggests that anatomically modern humans and their ancestors engaged in the harvesting of marine resources for at least 1.95 million years (Braun et al. 2010). The earliest evidence for the incorporation of fish proteins in hominin diets was found at an archaeological site in East Turkana, Kenya, dated to 1.95 million years, where the in situ butchered remains of fish, turtle, and crocodile were discovered (Braun et al. 2010). Evidence for the use of shellfish as part of the hominin diet extends over 700,000 years with the recovery of freshwater oyster shells in Kao Pah Nam Cave in Thailand (Pope 1989). Although the quantity of evidence supporting the use of aquatic resources prior to 130,000 years ago is scant, coastal archaeological records probably have been heavily affected by erosion, fluctuations in eustatic sea levels, and other taphonomic processes (Steele and Álvarez-Fernández 2011). Despite the deep antiquity of fishing and shellfishing by humans and their hominin ancestors, the impact of these activities on marine ecosystems is not well documented prior to the Holocene epoch. Several studies of shell middens from the Holocene, however, have demonstrated that increased predation pressure by humans had negative impacts to aquatic resources; most notably, reducing the average size and abundances of these resources and transforming local seascapes. California’s Northern Channel Islands have produced some of the earliest evidence for fishing, shellfishing, seafaring, and maritime adaptations in the New World, and a variety of historical ecological case studies demonstrate that increased predation pressure on marine resources by the Chumash and their ancestors led to a reduction in the average size of several marine species through time (see Braje et al. 2007; Braje et al. 2012a, 2012b; Erlandson, Braje, Rick, Jew, Kennett, Dwyer, Ainis, Vellanoweth, and Watts 2011; Raab 1992). Using allometric approaches common in zooarchaeological studies, researchers have collected size

measurements from archaeological specimens and used the average size through time as a proxy for the health and stability of important prey species. Declines in overall size not attributed to fluctuations in climate (e.g., sea surface-temperature and marine productivity) are ascribed to human overharvesting. The archaeological remains of several species including California mussel (Mytilus californianus), red and black abalone (Haliotis rufescens and H. cracherodii), owl limpets (Lottia gigantea), and rockfish (genus Sebastes) have been used for such studies (Braje et al. 2007, 2012a, 2012b, 2015; Erlandson et al. 2008; Erlandson, Braje, Rick, Jew, Kennett, Dwyer, Ainis, Vellanoweth, and Watts 2011; Erlandson, Ainis, Braje, Jew, McVey, Rick, Vellanoweth, and Watts 2015; Jazwa et al. 2012). California mussels have received significant attention due to their ubiquity in island shell middens. Nearly every one of the thousands of shell middens, ranging from Paleocoastal (> 10,000 cal BP) to Historical Period (post AD 1542) sites, on the Northern Channel Islands contains California mussel shells. Preservation and stratigraphic integrity of these sites are generally exceptional, due largely to the lack of burrowing animals, the calcareous nature of dunes and soils, and limited historical development. In many cases, however, sample sizes of whole mussel shell length measurements are limited due to taphonomic and cultural processes that cause shell fragmentation. Trampling by domesticated and wild animals introduced during the 19th and 20th century ranching period was particularly destructive, as cattle, deer, and elk would often bed down in shell midden soils. Some studies have relied on intensive surface collections from eroding shell midden strata and subsurface excavations to recover whole shells from radiocarbon dated archaeological deposits to establish average size proxies through time (see Braje 2010; Erlandson et al. 2008). Others have employed a template that estimates to within 1 centimeter (cm) the size of a California mussel shell based on the breadth of the hinge fragment (Braje et al. 2007; Jazwa et al. 2012; White 1989). Experimental work by Bell (2009), however, demonstrates that this template can produce unreliable results that are statistically inaccurate and not replicable between multiple zooarchaeologists. In an effort build statistically reliable methods for estimating total shell length of California mussels from hinge fragments, Campbell and Braje (2015) used an allometric approach to produce three statistically reliable regression formulas that use measurements collected from the commonly found hinge portion

to estimate total shell length (for related discussion see Campbell and Braje 2015; McKechnie et al. 2015; Singh and McKechnie 2015). Here, we use archaeological mussel shell length measurements collected using the umbo-width regression formula established by Campbell and Braje (2015) to extrapolate shell length data from fragmented California mussel shells. These data were collected from 16 prehistoric sites located on San Miguel, Santa Rosa, and Santa Cruz islands that were previously radiocarbon dated to the Early, Middle, and Late Holocene. Our data were compared to paleo-sea surface temperature records (SST) from the Santa Barbara Channel region to tease out whether declines in mussel shell length through time were the result of anthropogenic impacts or the result of climate variability. Finally, results were compared to shell length data for modern California mussel populations collected by National Park Service (NPS) Channel Islands biologists as part of the bi-annual intertidal monitoring program in spring 2014. These combined archaeological and modern datasets were used as a proxy to help assess the current health of California mussel populations. Our conclusions echo the sentiments of many historical ecologists who argue that in order to better manage modern ecosystems it is important to extend our management baselines and perspectives into the deep past (Crumley 1994; Jackson et al. 2001; Redman 1999; Rick and Lockwood 2013).

BACKGROUND California’s Northern Channel Islands are situated between 20 and 42 km offshore from the California coast. These islands are an extension of the Santa Monica Mountain Range and include, from east to west, Anacapa, Santa Cruz, Santa Rosa, and San Miguel islands. The islands range in size from 2.9 to 249 km² and boast diverse topography including mountains, sand dunes, tablelands, marine terraces, and extensive canyons (Schoenherr et al. 1999). The bathymetry surrounding the islands suggests that during the last glacial maximum (LGM), when eustatic sea levels were on average 120 m lower, the northern islands comprised a single island, Santarosae (Kennett 2005; Orr 1968). The steady rise of sea levels beginning ca. 18,000 years ago resulted in the inundation of low-lying portions of Santarosae, reducing the land mass by nearly 75 percent, and the fragmentation of Santarosae into the four smaller islands that exist today (Porcasi et al. 1999; Reeder-Meyers et al. 2015).

Separation from the mainland throughout the Quaternary resulted in low diversity in island terrestrial flora and fauna species when compared to the California mainland. The largest terrestrial mammal to occupy the Northern Channel Islands was the pygmy mammoth (Mammuthis exilis) and, despite evidence confirming their presence as late as 13,000 years ago, it is still unclear whether humans and mammoths co-existed on the islands (Johnson et al. 2000). Today, the largest endemic island mammal is the Channel Island fox (Urocyon littoralis), followed by the island spotted skunk (Spilogale gracilis amphiala) and the island deer mouse (Peromyscus maniculatus) (Schoenherr et al. 1999). While relatively impoverished when compared to the rich terrestrial plant foods of the mainland (acorns, seeds, etc.), island plants foods such as island blue dicks (Dichelostemma capitatum) were an important component of Channel Island economies throughout the Holocene (Gill 2014; Gill and Erlandson 2014). In contrast to the limited terrestrial resources, island marine ecosystems are incredibly diverse and highly productive and became the cornerstone of Channel Islander subsistence economies. Kelp forests, sandy beaches, and rocky intertidal habitats sustain hundreds of species of fish, birds, sea mammals, and shellfish. The Santa Barbara Channel marine environment benefits from localized nutrient-rich upwelling that promotes a diverse and productive ecosystem. Over 900 species of fish inhabit the Santa Barbara Channel (Love 1996), dozens of which were exploited prehistorically. Six different species of pinnipeds visit the area annually, and zooarchaeological evidence of all six species has been identified in the archaeological record. Shellfish species found in the intertidal, subtidal, sandy beach, and estuarine habitats are incredibly abundant and diverse throughout the Holocene. California mussels, red and black abalone, owl limpets, sea urchins, and black turban snails are common constituents in island shell middens and were important sources of protein and raw material for tool production and ornamental artifacts, including fishhooks, beads, and pendants (Hudson and Blackburn 1985). Archaeological evidence suggests that for over 13,000 years humans visited, occupied, and exploited Northern Channel Island resources (Erlandson et al. 2007, 2008; Erlandson, Rick, Braje, Casperson, Culleton, Fulfrost, Garcia, Guthrie, Jew, Kennett, Moss, Reeder, Skinner, Watts, and Willis 2011; Johnson et al. 2000; Kennett et al. 2008). The Island Chumash, maritime hunter-gatherers known for their sophisticated technologies and

social complexity, heavily relied on local marine resources, supplemented by cross-channel exchange networks with mainland peoples (Arnold 2001; Kennett 2005; Rick 2007), to sustain their growing populations and to compensate for the relatively depauperate terrestrial resources. At most terminal Pleistocene and Early Holocene sites for which quantified faunal data are available, shellfish dominate islander protein diets (Erlandson et al. 2004; Kennett 2005; Rick, Erlandson, Vellanoweth, and Braje 2005), although the recovery of lithic hunting tools at many early sites suggests that sea mammal hunting and fishing may have been more important to island economies than zooarchaeological analysis suggests (Erlandson, Rick, Braje, Casperson, Culleton, Fulfrost, Garcia, Guthrie, Jew, Kennett, Moss, Reeder, Skinner, Watts, and Willis 2011). Throughout the Holocene, shellfish remained a central subsistence resource, with plant foods and increasing, amounts of fish, marine mammals, and birds comprising Channel Islander diets for millennia (see Braje 2010; Rick, Erlandson, Vellanoweth, and Braje 2005). As part of a historical ecological study of human impacts on island intertidal ecosystems, Braje and colleagues (2007) ranked the ten most common prey shellfish species on the Northern Channel Islands. Based largely on size, ease of collection, and availability, Braje et al. (2007) established a human behavioral ecology framework for understanding how island fishers would target shellfish resources. Due to their extensive distribution, ease of collection and processing, and availability in dense clusters, California mussels were ranked as the top shellfish resource through time (Braje et al. 2007:739). In a related meta-analysis of shellfish exploitation on the Northern Channel Islands, Braje et al. (2012a) determined that archaeological shell middens dated to the terminal Pleistocene and the Early, Middle, and Late Holocene tend to be dominated by California mussels, which account, on average, for over 50 percent of the shellfish assemblage. These findings confirm the importance of California mussels to island diets throughout the Holocene and point to the tremendous human predation pressure exhibited on this resource.

CALIFORNIA MUSSEL ECOLOGY California mussels (Figure 7) are filter-feeding pelecypods (bivalves) found along rocky intertidal zones from the Aleutian Islands in the north to the Socorro Islands, Mexico, in the south (Jones and Richman 1995). More restricted than other mussel species by their

narrow ecological niche, they are found attached to rocks in rocky intertidal and subtidal habitats via byssal threads, easily accessible to humans, and often found exposed during low tides. Although commonly predated upon by humans in ancient times, most modern California mussel communities are not threatened by human predation as a subsistence resource. Current risks to their populations include the adverse effects of human recreational activities and their use as fishing bait (Roy et al. 2003). Additionally, anthropogenic climate change including rising sea surface temperatures and ocean acidification have been linked to declining populations and reductions in average shell length (Smith et al. 2008).

Figure 7. Watercolor of a Mytilus californianus shell with labels of several of the physiological features mentioned in the text.

California mussels often dominate intertidal communities, living in dense clusters of up to 1000 individuals per square meter within their habitat range (Jones and Richman 1995). They are distinguishable from other mussel species by their coarser, sturdier shell and prominent radiation ridges (Gosling 1992; Jones and Richman 1995). The largest California mussel was recorded by Suchanek (1986) at 266 mm; however, California mussels rarely exceed 180 mm in length (Jones and Richman 1995). They are common prey for many predators including waterfowl, sea otters (Enhydra lutris), and sea stars (Pisaster ochraceus). Sea stars are particularly voracious mussel predators, consuming up to 80 mussels per year, and prefer individuals that do not exceed 100 mm in length (Feder 1970). Storm events have also contributed to high instances of mortality for mussel species (Suchanek 1985). When a

mussel bed is cleared, either as the result of natural factors or predation, it takes at minimum two and a half years for the regeneration process to begin (Jones and Richman 1995). As mussels begin to repopulate the area, it can take between eight and 35 years for the area to return to pre-disturbance coverage. In highly sensitive environmental conditions, this process can take up to 100 years (Suchanek 1979). If left relatively undisturbed, a population can survive in an area for 50 to 100 years (Suchanek 1981). California mussel growth rates are highly dependent on environmental conditions (Coe and Fox 1942). Factors such as tidal height, food availability, water temperature, wave action, sex, and age influence growth rates. Growth continues throughout the life cycle of a California mussel; however, rates are most rapid during the first year with individuals reaching, on average, 51 mm (Coe and Fox 1942). The rate of growth remains high for the next two years with average size increases of 30 to 40 mm, and, after three years, growth rates slow considerably. Ideally, studies of the effects of human predation on the population structure of California mussels should include an analysis of the average age of death (Bailey and Milner 2008), however, methods for accurate estimates of archaeological samples are problematic. In addition, there are no available comparable modern datasets from the Northern Channel Islands of mussel age structure, here we use average shell length as a proxy. Several studies from the Northern Channel Islands have identified a significant reduction in mean mussel shell length over the last 10,000 years (Braje 2010; Braje et al. 2007; Erlandson et al. 2008; Erlandson, Braje, Rick, Jew, Kennett, Dwyer, Ainis, Vellanoweth, and Watts 2011; Jazwa et al. 2012). However, this research has primarily used only whole mussel shells to collect length measurements and most have focused on San Miguel Island, where whole mussel shells tend to be better preserved in archaeological shell middens. Others have relied on White’s template for estimating shell length from hinge fragments. In 2015, two new methods were developed for estimating the total shell length of a California mussel from the commonly recovered hinge portion of the shell (see Campbell and Braje 2015; Singh and McKechnie 2015). We conducted a comparative study to determine which method would be best suited for use on the mussel assemblages from the Northern Channel Islands. Based on the results, we determined that the umbo-width measurement defined by Campbell and Braje (2015) was most suited for California mussel

63 assemblages from the Northern Channel Islands. We then applied this method to samples of mussels from the Northern Channel Islands to expand estimates of average prey mussel shell length through time to Santa Cruz and Santa Rosa islands, and incorporates both whole and hinge fragment measurements of California mussel. Our study is also explicitly a historical ecological project. We are interested in comparing the average length of mussels in the archaeological record to the average length of modern mussels. These data extend our ecological baselines into the deep past and can help resource managers better evaluate the health and structure of modern mussel beds.

METHODS AND MATERIALS In 2014, Channel Islands National Park (NPS) marine biologists first began collecting size data for California mussels at several intertidal monitoring locations across the Northern Channel Islands (Figure 8). In addition to monitoring coverages of California mussels using photographs collected since the 1980s, biologists collected size data of individual California mussel shells from 1 x 1 meter grids as a proxy for mean mussel shell length for these discrete locations (Whitaker, personal communication 2014). These measurements were estimated to the nearest centimeter and offer the first measure of average California mussel shell length comparable to archaeological sizes for the Northern Channel Islands. To help control for geographic variation, we identified 16 archaeological sites (5 from San Miguel, 7 from Santa Rosa, and 4 from Santa Cruz) located near these NPS monitoring locations Archaeological sites were selected based on two criteria: (1) the deposit’s age had to be established via radiocarbon dating of marine shell or charcoal samples with all dates calibrated to calendar years; and (2) sites had to contain abundant whole California mussel shells and/or hinge fragments (for approximate locations of these sites see Figure 8). When appropriate sites meeting these criteria were identified, whole California mussel shells and hinge fragments were measured in the field. Our sampling strategy involved the identification of 1x 1 meter linear areas where large concentrations of California mussels were visible in embedded soils, often from sea cliff faces or arroyo exposures. We carefully sampled the full range of shell sizes represented by scouring the site surface for whole shells and hinge fragments of all sizes and by screening (1/16th-inch mesh) some eroded deposits (Figure 9). Due to US Navy and NPS access restrictions, archaeological sites on San Miguel

Island were selected based on the same above criteria from archaeological shell midden samples temporarily housed at San Diego State University’s Environmental Anthropology and Archaeology Laboratory. Whole California mussel shells and hinge fragments from San Miguel Island, as well as two samples from Santa Rosa Island (CA-SRI-2 and CA-SRI-163) curated at the Santa Barbara Natural History Museum, were measured in the laboratory.

Figure 8. Approximate locations of archaeological and modern sampling sites. 65

Figure 9. B. Campbell and S. Duncan collecting size data at an archaeological shell midden on the west coast of Santa Cruz Island, January 2015 (Photo Credit: H. Haas).

Two similar methods for estimating the total shell length of a California mussel from hinge fragments have been recently proposed (see Campbell and Braje 2015; Singh and McKechnie 2015). To determine which method was best suited for this study, we used a sample of mussels (n = 50) from an archaeological site on San Miguel Island, CA-SMI-232, to test the predictive power of the umbo-width method (Campbell and Braje 2015) and the umbo-thickness method (Singh and McKechnie 2015). Only whole mussels, with a known total shell length, were selected for this test. We collected measurement data in an Excel document and identified the mean shell length for the sample following methods described in Campbell and Braje (2015) and Singh and McKechnie (2015). These data were then compared using a Games and Howell test in SPSS to identify if either method produced a statistically significant difference of the mean when compared to the known mean shell length. Based on the results of the regression formula strength analysis, California mussel hinges were measured, either in the laboratory or the field, using the umbo-width method. Following methods detailed by Campbell and Braje (2015), the umbo-width of each hinge was measured three consecutive times by a trained zooarchaeologist using digital calipers.

The mean shell length was then calculated from these measurements and applied to the following formula:

y = 8.2026x + 1.5967, where y = total mussel shell length and x = umbo-width

The value then was inserted into the above equation and the estimated total shell length was calculated. When whole mussels shells were available, umbo-width measurements were compared to whole shell measurements on these specimens and used to confirm the reliability of our methodology. In addition to new size measurements compiled for this study, we also mined published sources for additional California mussel shell length measurements (e.g., Braje 2010; Braje et al. 2007; Erlandson et al. 2008). We entered all measurements for each site in millimeters, compiled data in Excel files, calculated means, ranges, maximums, minimums, and standard deviations for each assemblage. Mean shell length values were then plotted for each radiocarbon dated component. To test the statistical significance of trans-Holocene size changes by island and to conduct cross island comparisons during the Late Holocene and modern period, samples were pooled into four temporal sub-groups: Early Holocene (10,000 - 7,500 cal BP; n = 297), Middle Holocene (7,500 - 3,500 cal BP; n = 556), Late Holocene (3,500 - 130 cal BP; n = 1409), and Modern (2014 monitoring data; n = 395). A Brown-Forsythe and Welch test was conducted to assess the equality of the means; these tests are appropriate for use in statistical analyses when unequal sample sizes or unequal variance occurs (Tomarken and Serlin 1986). The Welch test result was preferred in all cases where Brown-Forsythe and Welch were disparate. We then applied the Games- Howell post hoc analysis to identify where statistically significant differences of means existed in our dataset. Significance level was consistent for all tests conducted (p < 0.05). All statistical analyses were conducted using SPSS software. Finally, these data were plotted against known periods of SST fluctuation to determine if variation in mean California mussel shell length could be attributed to natural climate variation (Kennett, D.J., B.J. Culleton, J.P. Kennett, J.M. Erlandson, and K.G. Cannariato 2007).

RESULTS A sample of 50 mussels from an archaeological site located on San Miguel Island, were measured to determine if the umbo-width method or the umbo-thickness method should be employed for this study (see Campbell and Braje 2015 for umbo-width method; Singh and McKechnie 2015for umbo-thickness method). Table 5 summarizes the results of the comparative analysis. The results suggest that although both the umbo-width regression formula and the umbo-length regression formula produced means that were statistically significantly similar to the known mean for shell length, the umbo-width method was more similar to the known mean for length (see Table 5). Therefore, we selected the umbo-width regression for use in this study.

Table 5. Umbo-Width and Umbo-Thickness Method Analysis Mean Shell Length Calculated Calculation Shell Length Max. Length Min. Length Method Count (n) (mm) St. Dev (mm) (mm) (mm) Known 50 34.65 10.35 76.37 20.45 Umbo-width 50 33.02 8.56 59.01 19.62 Umbo-thickness 50 38.12 9.58 62.55 20.44 Note: Millimeter (mm), standard (Std.), maximum (Max.) and minimum (Min.).

Table 6 summarizes data for the age, sample size, mean, minimum, maximum, and standard deviations of 2,262 California mussel shells from 16 prehistoric shell middens on Santa Cruz, Santa Rosa, and San Miguel islands. Table 7 summarizes data for the sample size, mean, minimum, maximum, and standard deviations of 395 California mussel shells from 9 of the 16 NPS monitoring locations. Of the 16 monitored locations 7 were devoid of California mussels, no size data is available for these locations. The largest samples come from Late Holocene sites (n = 1,409), followed by Middle Holocene (n = 556), modern (n = 395), and a single Early Holocene site from San Miguel Island (n = 297). Our Santa Barbara Channel-wide sample of mussel shell measurements documents a long-term trend of variation in shell size through the ancient record, followed by a rebound in shell size during the modern period for the Sane Miguel and Santa Rosa islands sample. For the Santa Cruz Island dataset, shell size has remained relatively consistent through the Holocene and Anthropocene.

Table 6. Summary Data for Archaeological Samples of California Mussel Mean Calculated Shell Max. Min. Site # Age (cal Sample Length St. Dev Length Length (CA-) BP) (n) (mm) (mm) (mm) (mm) SMI-232 1290 409 37.76 14.69 91.55 10.95 SMI-396 4600 89 53.17 15.74 89.69 18.03 SMI-575 6100 108 42.84 17.98 122.89 12.31 SMI-657 6190 34 46.49 17.11 114.00 21.72 SMI-608 9550 297 45.96 20.49 106.45 12.97 SRI-87 >350 200 36.80 9.86 100.96 20.82 SRI-2 1070 259 46.55 13.49 114.44 17.32 SRI-77 1260 49 37.14 8.62 66.92 22.57 SRI-163 1300 121 50.31 16.69 103.88 24.37 SRI-62 2680 88 54.61 14.12 101.78 29.62 SRI-667 4440 200 40.22 10.74 100.49 18.17 SRI-109 5790 100 54.77 13.75 89.20 27.85 SCRI-195 650 98 50.51 15.19 112.63 22.70 SCRI-330 790 100 50.58 14.04 87.86 20.27 SCRI-757 2860 85 43.17 11.60 83.54 14.97 SCRI-770 5870 26 42.49 11.31 77.80 29.98 Note: San Miguel Island (SMI), Santa Rosa Island (SRI), Santa Cruz Island (SCRI)

Table 7. Modern California Mussel Shell Length Data Mean Calculated Shell Max. Min. Length St. Dev Length Length Island Age Count (n) (mm) (mm) (mm) (mm) SMI Modern 92 67.5 25.83 150 20 SRI Modern 100 65 22.94 120 20 SCRI Modern 208 46.21 27.57 110 10 Note: San Miguel Island (SMI), Santa Rosa Island (SRI), Santa Cruz Island (SCRI).

Table 8. Mean Calculated Shell Length for California Mussels Mean Calculated Island Age Count (n) Shell Length (mm) St. Dev (mm) SMI EH 297 45.96 20.49 MH 230 47.37 17.60 LH 409 37.76 14.69 M 92 67.50 25.83 SRI MH 300 39.93 10.06 LH 717 44.81 14.44 M 100 65.00 22.94 SCRI MH 26 42.49 11.31 LH 283 48.33 14.15 M 203 46.21 20.48 Note: San Miguel Island (SMI), Santa Rosa Island (SRI), Santa Cruz Island (SCRI), Early Holocene (EH), Middle Holocene (MH), Late Holocene (LH), Modern (M).

Table 9. Games and Howell Post Hoc Test for San Miguel Island Data 95% 95% Confidence Confidence Mean Interval Interval (I) (J) Difference Std. Lower Upper VAR00001 VAR00001 (I-J) Error Sig. Bound Bound EH MH -1.41159 1.66164 .831 -5.6942 2.8711 LH 8.20075* 1.39354 .000 4.6088 11.7927 San M -21.53856* 2.94407 .000 -29.2019 -13.8752 Miguel MH EH 1.41159 1.66164 .831 -2.8711 5.6942 Island LH 9.61234* 1.36915 .000 6.0804 13.1443 M -20.12697* 2.93261 .000 -27.7623 -12.4917 LH EH -8.20075* 1.39354 .000 -11.7927 -4.6088 MH -9.61234* 1.36915 .000 -13.1443 -6.0804 M -29.73931* 2.78946 .000 -37.0221 -22.4565 M EH 21.53856* 2.94407 .000 13.8752 29.2019 MH 20.12697* 2.93261 .000 12.4917 27.7623 LH 29.73931* 2.78946 .000 22.4565 37.0221 Note: Early Holocene (EH), Middle Holocene (MH), Late Holocene (LH), Modern (M). *The mean difference is significant at the 0.05 level.

Table 10. Games and Howell Post Hoc Test for Santa Rosa Island Data 95% 95% Confidence Confidence Mean Interval Interval (I) (J) Difference Std. Lower Upper Santa VAR00001 VAR00001 (I-J) Error Sig. Bound Bound Rosa MH LH -4.87901* .79253 .000 -6.7400 -3.0180 Island M -25.06972* 2.36645 .000 -30.6907 -19.4487 LH MH 4.87901* .79253 .000 3.0180 6.7400 M -20.19071* 2.35654 .000 -25.7894 -14.5920 M MH 25.06972* 2.36645 .000 19.4487 30.6907 LH 20.19071* 2.35654 .000 14.5920 25.7894 Note: Middle Holocene (MH), Late Holocene (LH), Modern (M). *The mean difference is significant at the 0.05 level.

Table 11. Games and Howell Post Hoc Test for Santa Cruz Island Data 95% 95% Confidence Confidence Mean Interval Interval (I) (J) Difference Std. Lower Upper Santa VAR00001 VAR00001 (I-J) Error Sig. Bound Bound Cruz MH LH -5.83632* 2.37275 .049 -11.6616 -.0111 Island M -3.71393 2.94414 .421 -10.7589 3.3311 LH MH 5.83632* 2.37275 .049 .0111 11.6616 M 2.12239 2.11011 .574 -2.8497 7.0945 M MH 3.71393 2.94414 .421 -3.3311 10.7589 LH -2.12239 2.11011 .574 -7.0945 2.8497 Note: Middle Holocene (MH), Late Holocene (LH), Modern (M). *The mean difference is significant at the 0.05 level.

Our results tracked changes in average mussel shell length by island; therefore, we conducted the Games and Howell statistical analyses for time period (Early, Middle, and Late Holocene and modern) for each island (San Miguel, Santa Rosa, and Santa Cruz). Additional tests included comparing the Late Holocene, and modern period datasets for each island. No comparison was conducted for the Early Holocene because of the limited data that was collected for this period. Our results suggest that there is a statistically significant difference in modern sizes when compared to measurements from the Early, Middle, and Late Holocene for San Miguel and Santa Rosa islands. Significant declines in mean mussel shell length were identified for all three islands studied through the Holocene.

The San Miguel Island datasets expressed a statistically significant difference in mean shell length for all temporal periods with the exception of the Early Holocene and Middle Holocene where no difference was observed (Table 9). On Santa Rosa Island statistically significant differences of means were observed for each time period (Table 10). On Santa Cruz Island, our analysis showed only a slight statistically significant difference in mean shell length from the Middle Holocene and Late Holocene assemblages and interestingly, found no significant difference in mean shell length when these periods were compared to the modern period (Table 11).

Table 12. Games and Howell Post Hoc Test for Late Holocene California Mussel Data 95% 95% Confidence Confidence Mean Interval Interval (I) (J) Difference Std. Lower Upper VAR00001 VAR00001 (I-J) Error Sig. Bound Bound Late SMI SRI -7.04860* .90465 .000 -9.1726 -4.9246 Holocene SCRI -10.56860* 1.11131 .000 -13.1795 -7.9577 Data SRI SMI 7.04860* .90465 .000 4.9246 9.1726 SCRI -3.52000* .99896 .001 -5.8679 -1.1721 SCRI SMI 10.56860* 1.11131 .000 7.9577 13.1795 SRI 3.52000* .99896 .001 1.1721 5.8679 Note: San Miguel Island (SMI), Santa Rosa Island (SRI), Santa Cruz Island (SCRI) Note*: The mean difference is significant at the 0.05 level.

Table 13. Games and Howell Post Hoc Test for Modern California Mussel Data 95% 95% Confidence Confidence Mean Interval Interval (I) (J) Difference Std. Lower Upper VAR00001 VAR00001 (I-J) Error Sig. Bound Bound Modern SMI SRI 2.50000 3.53779 .760 -5.8597 10.8597 Data SCRI 21.29310* 3.31642 .000 13.4579 29.1283 SRI SMI -2.50000 3.53779 .760 -10.8597 5.8597 SCRI 18.79310* 3.00132 .000 11.7135 25.8727 SCRI SMI -21.29310* 3.31642 .000 -29.1283 -13.4579 SRI -18.79310* 3.00132 .000 -25.8727 -11.7135 Note: San Miguel Island (SMI), Santa Rosa Island (SRI), Santa Cruz Island (SCRI) Note*: The mean difference is significant at the 0.05 level.

A Levene Statistic, and subsequent Games and Howell analysis, was conducted using the Late Holocene data to identify statistical significant difference between the mean shell

73 length for each of the three islands sampled (Table 12). The results of this test indicated that the mean shell length for each island during the Late Holocene was significantly different. Santa Cruz Island samples produced the largest mean shell length (48.3 mm), followed by Santa Rosa Island (44.8 mm) and San Miguel Island (37.8 mm). Of the modern dataset, San Miguel Island samples produced the largest mean shell length (67.5 mm), followed by Santa Rosa Island (65 mm) and Santa Cruz Island (46.21 mm). When considering only the modern data, we used the Games and Howell Post Hoc analysis to determine if there is a statistically significant difference in average mussel shell length. The results of these tests suggest that when San Miguel and Santa Rosa islands datasets are compared to Santa Cruz Island a statistically significant difference in the mean shell length does exist (Table 13). These finding suggest important differences in the average shell length of mussel across the Santa Barbara Channel. This phenomenon is discussed in greater detail below.

Figure 10. Trans-Holocene changes in mean California mussel shell length measurements for 16 Channel Island archaeological components compared to broad scale Holocene SST changes from the Santa Barbara Basin; W=Warm, C= Cold, N=Neutral, Source: Kennett, D.J., J.P. Kennett, J.M. Erlandson, and K.G. Cannariato 2007

The mean shell length data for California mussels from each of the 16 sampled archaeological sites were compared to broad scale Holocene SST changes for the Santa Barbara Basin (Kennett, D.J., J.P. Kennett, J.M. Erlandson, and K.G. Cannariato 2007). No correlations were observed between California mussel shell length and these cooling and warming SST trends (Figure 10).

DISCUSSION AND CONCLUSIONS Historical ecologists have demonstrated the importance of consulting the archaeological and ethnographic record when establishing restoration and baseline targets for marine resource conservation (see Jackson et al. 2001). This is especially true in areas where human-environment interactions over the longue-durée have led to widespread ecological changes. On the Channel Islands, thousands of years of settlement and subsistence activities including extensive fishing and shellfishing during the prehistoric and historical periods and cattle ranching over the past two centuries led to a transformation of both the land and the seascape. Studies from the Channel Islands have found that declines in the average shell size of several intertidal shellfish species occurred over the last 10,000 years and were the result of intense predation by humans (Braje et al. 2007, 2012a; Erlandson et al. 2008; Erlandson, Braje, Rick, Jew, Kennett, Dwyer, Ainis, Vellanoweth, and Watts 2011; Erlandson, Ainis, Braje, Jew, McVey, Rick, Vellanoweth, and Watts 2015). For California mussels, Erlandson and colleagues (2008) demonstrated a reduction in mean shell length using archaeological samples from San Miguel Island. Using the umbo-width regression formula established by Campbell and Braje (2015) our study identified similar trends for California mussels from San Miguel Island with different patterns identified for Santa Rosa and Santa Cruz islands. California mussel shell length on San Miguel Island generally decreases through the Holocene. This decline in mean shell length was followed by a subsequent rebound in modern mean shell length; mean shell length of the modern sample recorded on San Miguel Island is nearly twice the mean shell length that was measured for the Late Holocene (see Table 7). Declines in the mean shell length for mussels sampled from Santa Rosa Island were not identified when the Middle and Late Holocene were compared; interestingly, shell length during the Late Holocene was statistically significantly larger than during the Middle Holocene. Comparisons of the Late Holocene and modern data, however, suggest a similar

75 trend to the San Miguel Island data; mean shell length increased approximately 21 mm when the Late Holocene sample was compared to the modern sample for the island. Despite several thousands of years of intense human predation and subsequently being relatively free from predation for the past 150 years, mean length of California mussel has remained consistent throughout the Late Holocene and modern period on Santa Cruz Island. A statistically significant increase in mean shell length occurred on Santa Cruz Island between the Middle Holocene and Late Holocene a trend that continues through the modern period. To determine if fluctuations in shellfish size correspond to warming and cooling trends in SST, several researchers have looked for patterns in their data to suggest a natural cause for this reduction in mean shell length through time (Braje and Rick 2011; Braje et al. 2012a; Erlandson et al. 2008; Erlandson, Braje, Rick, Jew, Kennett, Dwyer, Ainis, Vellanoweth, and Watts 2011). These studies found no clear relationship between SST and the mean shell length of intertidal shellfish. Similarly, we were unable to identify a clear trend to suggest that SST was the predominant factor influencing changes in California mussel shell length (see Figure 10). The combined analyses suggest that some other factor, possibly related to human predation of California mussels on San Miguel and Santa Rosa islands likely led to a reduction in mean shell length, specifically during the Late Holocene. The Late Holocene length reduction correlates with the generally agreed upon population increase that occurred on the Northern Channel Islands during this time (Arnold 2001; Erlandson et al. 2001; Glassow 1999). Additionally, the expansion of sedentary villages would have placed increased pressure on shellfish as a subsistence resource, leaving little time for intertidal species to reach their maximum growth potential. Trends in our modern dataset suggest that environmental conditions such as localized marine upwelling likely have a strong influence over the temporal rate for re-establishing a healthy California mussel population following periods of intense pressure caused by excessive predation or die-off events. Fenberg and colleagues (2015) suggest that the genus Mytilus is extremely sensitive to upwelling conditions which can influence larval dispersal and food availability. The Santa Barbara Channel is well-known as a transitional zone where a confluence of differing circulation patterns, warm and cool water temperatures, and strong and weak upwelling occurs, specifically in the waters off of San Miguel Island (Wares et al. 2001). Our modern data suggests a dramatic increase in mean shell length along the east to

76 west gradient suggesting that localized upwelling in the waters surrounding San Miguel and Santa Rosa islands may be heavily influencing the population structure and increase in mean shell length of California mussels in these areas. This east to west trend in mean shell length does not exist for our Middle or Late Holocene datasets. This research suggests that human predation heavily influenced mean shell length of shellfish during the prehistoric occupation of the Northern Channel Islands. Despite long-term predation pressure by the Chumash and their ancestors, California mussel populations remained an important protein source throughout the Holocene (see Braje et al. 2012a). The fact that California mussels never disappear from the archaeological record suggests that this resource may have been actively managed by the Chumash, especially following the establishment of permanent villages and chiefdoms. After large coastal villages are established after ca. 1,500 cal BP and populations explode, the Chumash demonstrate relatively little settlement mobility. This would have been the time when local intertidal systems would have been under the greatest human predation pressure. Although the Chumash begin to fish in near shore and kelp forest habitats more intensively, intertidal shellfish remain a central component to the protein diet. The ethnographic record suggests that Paralytic Shellfish Poisoning (PSP), an illness caused by the ingestion of shellfish due to the marine dinoflagellate (Alexandrium catenella) common during warmer summer months (i.e. red tide events), likely occurred during the prehistoric period (Gifford 1967; Greengo 1948, 1952; Hallegraeff 1995; Horner et al. 1997). Some Native American informants discussed with anthologists the taboo of consuming shellfish during red tide events. These periods of resource avoidance would have halted shellfish collection for several months out of the year, giving California mussel populations some relief from harvesting activities. Additionally, chiefly ownership of resources within Chumash society has been documented (see Arnold 2007 and Gamble 2008 for a discussion of tomol ownership). It is possible that as permanent settlements arose across the Northern Channel Islands, chiefs may have claimed ownership of marine resources located near or adjacent to their villages. Such ownership would have likely led to some form of management to ensure the stability of intertidal resources including the California mussels. Ownership of local resources has been documented for other traditional groups of California

77 including the Tolowa who claimed ownership over fishing places near Lake Earl and Lake Talawa (Gould 1975). California mussels also may have remained relatively stable due to human predation strategies. Plucking large or medium size mussels may have allowed a juvenile seed population that could rejuvenate mussel beds in a relatively short time. Plucking was likely the harvesting strategy through time as human behavioral ecology studies suggest that is was a more optimal strategy than stripping an entire bed (see Jones and Richman 1995). In much the same way, harder-to-access lower intertidal or upper subtidal California mussel populations may have remained relatively free of predation pressure and provided the seed population to rejuvenate human harvested mussel beds. California mussels have been relatively free from human predation pressure on the Channel Islands for over 150 years. The two main non-human predators of the California mussel, the sea otter and the sea star, have either been absent from the region for over a century or have undergone massive population declines due to destructive diseases. Sea otters were eradicated from the Northern Channel Islands during the historical fur trade and have only recently been reintroduced to waters surrounding San Nicolas Island, but have not been allowed to re-establish populations along the Santa Barbara Channel over fears of their potential impacts to abalone recovery and commercial urchin fisheries (see Fanshawe et al. 2003). Furthermore, the sea star has recently suffered a massive die-off linked to Sea Star Wasting Disease (Hewson et al. 2014). First recognized in June 2013, this disease has caused irrevocable damage to sea star populations along the Pacific coast. As the main predator of the California mussel, sea stars control the habitat range of California mussels with fluctuations in California mussel habitat range occurring as a result of the presence or absence of sea stars in an area, regressing when sea stars are near and flourishing when they are not. The significant increase in California mussel shell length on San Miguel and Santa Rosa islands during the modern period may be the result of a population boom following their release from sea star predation, however this does not seem likely as mussel growth over a one to two year period would not be substantial. However, this does not explain the apparent lack of rebound during the Santa Cruz Island modern period, where sea star populations have also experience catastrophic declines (Hewson et al. 2014). Continued study of modern California mussel populations will further elucidate these trends to

78 determine if the modern mean shell length identified here is in fact, representative of a healthy California mussel population and suitable as a baseline for management. Using archaeological samples as a proxy, we have identified that modern mean shell length for California mussels as being larger today than at any point during the Holocene occupation of San Miguel and Santa Rosa islands. This increase in mean shell length during the modern period for Santa Cruz Island suggests that other factors not considered here may be influencing the growth of California mussels. The research presented here is part of a larger study of over 12,000 years of human impacts on California mussel populations from the Northern Channel Islands (see Erlandson et al. 2008). Our study contributes data generated by a new historical ecological method for assessing the long term history of California mussels on the Northern Channel Islands by incorporating not only measurements of whole shells but also hinge fragments using a statistically reliable method. These data contribute to a growing collection of data for California mussel shell length during the Holocene. Additionally, we have begun to address human impacts on California mussels on Santa Rosa and Santa Cruz islands. Our preliminary research suggests that localized environmental phenomenon likely plays a substantial role in the rehabilitation of mussel populations in the channel, indicating that each island may exhibit different trends in California mussel shell length distribution. It is critical that additional data be collected for these islands to fully understand the patterns and trends influencing California mussel populations in order to establish better informed baseline data for this species. Humans and their ancestors have utilized marine resources with increasing intensity for thousands of years (Jackson et al. 2001; Rick and Erlandson 2008). This intense predation has no doubt led to several periods of reorganization in marine environments; specifically, rocky intertidal zones where the removal of a single species can lead to the transformation of habitat ranges for other species (e.g. see Paine 1969 for a discussion of the relationship between sea stars and California mussels). Archaeological data can be used to help decipher the deeper ecological histories of specific areas and provide valuable information about the structure of nearshore ecosystems in the distant past as well as the processes involved in the creation of the anthropogenic land and seascapes during the Anthropocene. Building effective management and restoration plans requires information regarding historical and ancient harvests and the establishment of reference points (baselines) that account for

79 overfishing, other anthropogenic disturbances, or natural climatic fluctuations (Dayton et al. 1998; Jackson et al. 2001; Pauly 1995; Pauly et al. 1998; Tegner and Dayton 2000).

CHAPTER 8

SUMMARY AND CONCLUSIONS

Using the archaeological record to reconstruct species profiles during the prehistoric period can and does present numerous challenges. California mussels, for example, rarely remain intact in archaeological contexts. Natural and cultural taphonomic processes often cause these shells to fracture, making it difficult to extract size data which are often used as a proxy for population health. Despite these challenges, the results of this research effectively demonstrate that archaeological data can provide insightful information for modern resource managers especially when determining baseline targets for resource management. Here, I have used an allometric approach to identify correlations between physical elements found on the hinge of a California mussel and the total shell length. Of the three elements tested, the umbo-width measurement had the highest r-squared value of 0.9302. After testing this method on an archaeological sample of California mussels, this method was further validated, estimating the total shell length of each mussel to within 1 cm. This method was further validated in a recent publication by Singh and McKechnie (2015) who also applied the allometric approach to physical elements not utilized here and found similar correlations to total shell length. These studies suggest that the allometric method has several benefits and may be applied more widely to other marine and terrestrial species to provide significantly more accurate and reliable datasets when using archaeological record. With historical ecology gaining in popularity among researchers it is critical that research methods be refined and perfected. By establishing a method for estimating California mussel shell length from the commonly found hinge, researchers will no longer be limited due to taphonomic or preservation issues and can establish more complete size profiles for California mussels throughout the Holocene. Additionally, this method will allow researchers to collect data in the field with relative ease. Although limitations do exist, including human bias associated with the formation of the archaeological record, research by White (1989) and

Bouey and Basgall (1991) suggest that by using size ranges and age at death studies for species studied, researchers may be able to eliminate or at least compensate for such biases. The umbo-width regression formula was applied to a large (n = 2,262) sample of California mussels from archaeological contexts. The outcomes of this research suggest that California mussels were statistically significant smaller during the Middle and Late Holocene occupation of San Miguel and Santa Rosa islands than they are today. This increase in shell length during the modern period is likely the result of the cessation of human harvesting; however other contributing factors such as environmental conditions in the region and the removal and die-off of the two main non-human predators of the California mussel have no doubt been influential in this dramatic shell length increase. Data from Santa Cruz Island, however, suggest that a statistically significant increase in mean shell length occurred from the Middle to Late Holocene, no significant increase in mean shell length has taken place during the modern period. Further data collection will be necessary to further explicate these trends. The research presented in the previous chapter contributes new information to a larger study of over 12,000 years of human impacts on California mussel communities on the Northern Channel Islands. Furthermore, the results of the stand-alone island studies implicate the importance of localized studies in marine historical ecology. It is becoming increasingly apparent that many nearshore marine habitats have been fished with intensities sufficient to alter ecosystem structures for thousands of years (Jackson et al. 2001; Rick and Erlandson 2008). Using archaeological data to help decipher the deeper ecological histories of specific areas and fisheries can provide valuable information about the structure of nearshore ecosystems in the distant past as well as the processes involved in the creation of the anthropogenic land and seascapes during the Anthropocene. Building effective management and restoration plans requires information regarding historical and ancient harvests and the establishment of reference points (baselines) that account for overfishing, other anthropogenic disturbances, or natural climatic fluctuations (Dayton et al. 1998; Jackson et al. 2001; Pauly 1995; Pauly et al. 1998; Tegner and Dayton 2000). My research can help resource managers better manage intertidal ecosystem resources that will likely face significant pressures in the coming decades.

FUTURE DIRECTIONS The archaeological record can enhance our understanding of human-environmental relationships through human history. Shell middens on the Channel Islands can illuminate for researchers not only what humans were consuming, but how their consumption may have fundamentally altered local ecosystems and ecologies. My research provides the building blocks for the development of new allometric approaches for establishing reliable zooarchaeological methods to help researchers investigate anthropogenic and natural impacts on prehistoric land and seascapes. Future directions for this research include several possible analyses. First, the modern sample of California mussels used to create our regression formulae came from a single location in San Diego. Because several environmental conditions can influence growth patterns in California mussel, it would be beneficial to create several more localized regression formulae for each of the Channel Islands. The expansion of our modern dataset to include mussels of increased length (> 90 mm) would also be beneficial (see Singh and McKechnie 2015). Additionally, the sample from Santa Cruz Island and the Early Holocene sample included in the second phase of this study were much smaller than the samples for other localities and time periods. I would like to continue to expand this dataset to include several new assemblages to contribute additional data to larger studies of human impacts on California mussels, as well as to expand these studies to San Diego and other coastal areas.

REFERENCES

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