Human Impacts on Seals, Sea Lions, and Sea Otters: Integrating Archaeology and Ecology in the Northeast Pacific

1

People, Pinnipeds, and Sea Otters of the Northeast Pacific

Torben C. Rick, Todd J. Braje, and Robert L. DeLong

MARINE MAMMALS, SUCH AS polar bears, sea otters, seals, sea lions, and walruses, are an extraordinary group of organisms, many of which maintain a link to both aquatic and terrestrial habitats. Often highly intelligent with sophisticated communication systems, marine mammals are a fundamental component of marine ecosystems around the world (Berta et al. 2005; Riedman 1990). Human interaction with seals, sea otters, and other marine mammals spans millennia and the entire globe (Erlandson 2001; Etnier 2007; Hildebrandt and Jones 1992; Klein and Cruz-Uribe 1996; Lyman 1995; McNiven and Beddingfeld 2008; Monks 2005a; Nagaoka 2002; Stringer et al. 2008). Containing large amounts of meat, oil, ivory, and other important raw material and dietary resources, pinnipeds (seals, sea lions, and walruses) and sea otters have been hunted and scavenged by people in the northeastern Pacific for much of the Holocene or earlier (Braje 2010; Broughton 1994, 1999; Burton et al. 2001, 2002; Colten 2002; Corbett et al. 2008; Crockford and Frederick 2007; Domning et al. 2007; Erlandson al. 2005; Etnier 2002a, 2002b, 2004, 2007; Gifford-Gonzalez et al. 2005; Hildebrandt and Jones 1992, 2002; Jones and Hildebrandt 1995; Lyman 1991, 1995, 2003; Moss et al. 2006; Newsome et al. 2007; Porcasi et al. 2000; Rick et al. 2009). The large terrestrial breeding colonies of some pinnipeds have made them highly susceptible to human hunting in the distant and near past. During the fur and oil trade of the 18th and 19th centuries, for example, human hunting of pinnipeds and sea otters decimated marine mammal populations, causing the extirpation of local populations of sea otters (Enhydra lutris), Guadalupe fur seals (Arctocephalus townsendi), and northern elephant seals (Mirounga angustirostris) and the extinction of the Steller’s sea cow (Hydrodamalis gigas; Ellis 2003; Ogden 1941; Scammon 1968). Archaeological data demonstrate that human impacts on marine mammals in the more distant past were also substantial and suggest that much remains to be learned about the prehistory of these animals.

With the recognition that human occupation of the world’s coastlines has great time depth (Bailey 2004; Erlandson 2001), research on ancient human impacts and influences on the biogeography, behavior, and ecology of pinnipeds, sea otters, and other marine organisms has increased. The shifting baselines phenomenon (Pauly 1995)—the notion that modern and historical ecosystems have been fundamentally altered by humans and that ecological baselines or benchmarks change dramatically over time—has prompted researchers from a variety of disciplines to emphasize the importance of archaeological and historical data in the management and restoration of marine ecosystems around the world (Erlandson and Rick 2010; Jackson et al. 2001; Pinnegar and Engle-hard 2008; Rick and Erlandson 2008). Faunal remains found in archaeological sites contain vast amounts of information on the composition, biogeography, and abundance of animals that were present in the past, as well as changing climatic conditions, human subsistence practices, and similarities and differences with the present day (see Lyman 2006; Lyman and Cannon 2004). Although the potential of these data remains underexplored, several recent studies have demonstrated the utility of archaeology for informing contemporary conservation issues, including the historical ecology of seals, sea lions, and sea otters (Lyman 2003; Etnier 2004, 2007; Hildebrandt and Jones 2002; Newsome et al. 2007; Rick et al. 2009).

Using historical ecology as a baseline (Crumley 1994), this volume brings together researchers from a variety of disciplines seeking to integrate archaeology, history, and ecology to understand the ancient and modern interactions between pinnipeds, sea otters, people, and marine ecosystems. Transcending disciplinary boundaries, the studies in this volume use ancient DNA (aDNA), stable isotopes, zooarchaeology, and other analytical techniques to understand the influence of ancient peoples on the biogeography, breeding behavior, and abundance of seals and sea lions over the last several millennia in the northeastern Pacific. While focused on pinnipeds and sea otters, these studies serve as a model for how archaeological data can significantly enhance the contemporary management and conservation of marine and terrestrial ecosystems.

Believing that the past is the key to understanding the present, we also recognize that documenting the interactions between ancient marine mammals and humans requires a firm grasp of the modern ecology of these organisms. Following a brief discussion of archaeology and human environmental impacts, this chapter provides an overview of the ecology of pinnipeds and sea otters in the northeastern Pacific, emphasizing the historical and modern transformations of these various populations (Figure 1.1).

ARCHAEOLOGY, HUMAN ENVIRONMENTAL IMPACTS, AND MARINE MAMMALS

Archaeologists have long investigated the interactions between humans and the environments in which they lived, often seeking to understand the impacts of environmental and climate change on the evolution of human society. More recently, archaeologists and anthropologists have debated the effects of ancient human subsistence, foraging, hunting, and other activities on the ecosystems where people resided (Hames 2007; Kay and Simmons 2002; Kirch 2005; Redman 1999). Assessing the environmental impacts of hunter-gatherers and other small-scale societies has been particularly contentious, with some scholars arguing that these peoples were inherent conservationists and environmental managers and others arguing they lack conservation principles and were generally self-centered and individualistic (see Alvard 1998; Hunn et al. 2003; Hames 2007; Hayashida 2005; Smith and Wishnie 2000). Although hotly contested, recent research suggests that ancient peoples from small-scale hunter-gatherers to stratified agriculturalists had a significant influence and impact on the environment (Kirch 2005; Kay and Simmons 2002; Redman 1999; Rick and Erlandson 2009). Ancient environmental interactions were extremely diverse, ranging from degradation to enhancement, raising significant questions about the structure and function of ancient and modern ecosystems.

FIGURE 1.1. Western North America and the northeastern Pacific showing the location of many areas discussed in the book, important pinniped breeding areas (Pribilof, San Miguel, and Guadalupe Islands), and the Commander Islands, the last known historical respite for sea cows.

Archaeological analyses of pinniped and sea otter remains have played an important role in broader debates over ancient human environmental impacts, providing important lessons for conservation biology (Etnier 2007; Lyman 2006, this volume). During the last two decades, archaeologists have debated the effects of ancient human hunting on northeastern Pacific Coast seals, sea lions, and sea otters (Etnier 2007; Hildebrandt and Jones 1992; Jones and Hildebrandt 1995; Lyman 1988, 1995, this volume; Moss et al. 2006; Newsome et al. 2007). These and other studies document significant changes in the distribution, abundance, and breeding behavior of pinnipeds and sea otters through time. For example, elephant seals are currently among the most numerous pinnipeds in coastal California, but few archaeological sites contain their remains, suggesting they were rare or absent for much of the last 10,000 years (see Braje et al., this volume; Hildebrandt and Jones 2002; Lyman, this volume; Rick et al. 2010). Similarly, Guadalupe fur seals are currently rare in coastal waters north of Baja, but they are found in archaeological sites as far north as British Columbia and Washington and are among the most common pinnipeds in coastal California archaeological sites (Braje et al., this volume; Etnier 2002b; Lyman, this volume; Moss et al. 2006; Rick et al. 2009). Explored in detail throughout this volume, these and other patterns appear to result from a variety of factors (e.g., climate change and human predation) that vary through time and across space.

With contemporary marine and terrestrial ecosystems around the world in a state of crisis, the studies in this volume use detailed investigations of the archaeology and historical ecology of northeastern Pacific pinnipeds and sea otters to inform contemporary problems. Restoring, managing, and regulating contemporary ecosystems and fisheries is a challenging and often political task that requires carefully balancing the diverse interests of the public, scientists, fishermen, policy makers, and numerous other stakeholders. To help inform these often difficult and contentious issues, the research presented in this volume relies on long-term reconstructions of ancient human interactions with sea otters and pinnipeds to focus on a series of key questions. How did ancient peoples from southern California to Alaska influence and impact ancient pinniped and sea otter abundance, biogeography, and behavior, and what can this tell us about ancient human-environmental interactions more generally? How have humans affected the location and breeding behaviors of pinniped and sea otter populations? What were the effects of ancient climatic changes on pinnipeds, sea otters, and human society, and how do we differentiate between the effects of human impacts and natural climatic changes? What was the role of ancient human technological change, social systems, ideology, and ritual in guiding the types of marine mammals that were taken? How can various analytical techniques, such as aDNA and stable isotope analyses, be integrated with traditional archaeological data to provide a more comprehensive understanding of ancient pinniped and sea otter populations? How can reconstructions of ancient human, pinniped, and sea otter interactions that span millennia inform the contemporary management of these organisms and broader marine ecosystems?

To address these questions, the chapters in this volume present up-to-date archaeological analyses and syntheses of specific regions throughout the northeastern Pacific. Many of these studies note significant differences between ancient and modern pinniped and sea otter abundance, biogeography, and behavior, challenging conventional wisdom about the structure and composition of contemporary pinniped and sea otter populations. In the final chapter, we use the case studies presented in this volume to revisit these questions and explore the challenges presented when archaeological data are incongruent with the modern situation.

ECOLOGY, BEHAVIOR, AND DISTRIBUTION

During the Holocene, eight major species of pinniped, sea otter, and sea cow were exploited by ancient humans throughout much of the northeastern Pacific (Table 1.1). This includes four otariids (eared seals), two phocids (true seals), a sea otter, and an extinct sea cow. The four major otariid species on the Pacific Coast from southern California to the Aleutians include two sea lions (Eumetopias jubatus [Steller sea lion] and Zalophus californianus [California sea lion]) and two fur seals (Callorhinus ursinus [northern fur seal] and Arctocephalus townsendi [Guadalupe fur seal]). Two phocids range widely in the Northeastern Pacific: Mirounga angustirostris (northern elephant seal) and Phoca vitulina (harbor seal). The sea otter, Steller’s sea cow (Domning et al. 2007), and walrus (Odobenus rosmarus) were the other similar marine mammal species in the northeastern Pacific. A few other seals (e.g., ribbon seals [Histriphoca fasciata] and spotted seals [Phoca largha]) also venture into the far northern parts of the Pacific. The ecology of some of these seals, as well as walruses, is covered in depth in chapters by Hill (Chapter 3) and Crockford and Frederick (Chapter 4) and is not repeated here.

TABLE 1.1

Summary of Modern Distribution and Status of Pinnipeds, Sea Otters, and Sea Cows of the Northeastern Pacific

Pinnipeds and sea otters have long evolutionary histories. The earliest well-documented fossil pinnipeds come from the late Oligocene, roughly 27 to 25 million years ago (MYA), but there is evidence that pinnipeds may be as old as 29 MYA (Berta et al. 2005:27). Morphologic and molecular analyses suggest that pinnipeds are likely monophyletic and most closely aligned with arctoid (raccoons, weasels, bears, etc.) carnivores, especially mustelids (weasels) and ursids (bears; Berta et al. 2005; Jefferson et al. 2008). The earliest phocids may appear as early as 29–23 MYA, with well-dated specimens appearing around 15 MYA (Berta et al. 2005). Fossil otariids currently appear around 11 MYA in the northeastern Pacific. The modern sea otter (Enhydra) arose more recently than the pinnipeds around 1–3 MYA in the North Pacific (Berta et al. 2005:104). Human exploitation of these species likely extends back to initial human colonization of North America during the terminal Pleistocene, with definitive archaeological evidence of interaction during the Early to Middle Holocene and of intensive harvest during the Late Holocene (see Hildebrandt and Jones 1992).

The contemporary distribution and breeding behaviors of pinnipeds and sea otters are constantly changing due to a variety of cultural and environmental variables. As the remaining chapters in this volume show, this is something that has occurred in deeper archaeological time as well. The modern and historical behaviors of these animals form an important backdrop for interpreting the archaeological data.

OTARIIDS

There are currently about 16 species of otariids around the world, with four found in the northeast Pacific (Jefferson et al. 2008). The Steller sea lion is the largest of the North Pacific otariids and displays marked sexual size dimorphism, with males up to 325 cm in length and 1120 kg in mass and females up to 291 cm in length and 350 kg in mass (Loughlin et al. 1987). During modern and recent historical times, Steller sea lions ranged from Hokkaido, Japan, around the northern Pacific Rim, and down to the California Channel Islands (Loughlin et al. 1987; Riedman 1990). The population has been declining through portions of its range in recent decades, but Steller sea lions still breed on islands in the Bering Sea, the Aleutians, the Gulf of Alaska, southeast Alaska, British Columbia, Oregon, and in California south to Año Nuevo Island and populations have been increasing from Oregon to southeast Alaska since the 1970s. The species is currently listed by the International Union for the Conservation of Nature (IUCN) as endangered (Jefferson et al. 2008), and it is listed under the U.S. Endangered Species Act (ESA) as endangered in the western portion of the range (Central Gulf of Alaska, westward) and as threatened in the eastern portion of the range (Central Gulf of Alaska to Central California). Steller sea lions feed on fish, cephalopods, and crustaceans, as well as occasionally on harbor seals, northern fur seals, and possibly sea otters (Loughlin et al. 1987).

Generally regarded as nonmigratory, Steller sea lions are known to disperse fairly widely several months after breeding between late May and early July. Consequently, Hildebrandt and Jones (1992) and other archaeologists have referred to Steller sea lions, the other otariids, and northern elephant seals as migratory breeders or, more recently, as terrestrial breeders because of the large breeding groups they establish on land (Jones et al. 2004) and their seasonal abundance that would make them more susceptible to human predation (see Etnier 2007 for a critique). Steller sea lions are polygynous, mating and pupping on land in territories defended by males. Females give birth to a single pup in May or June and begin a typical otariid pattern, feeding at sea and returning to the rookery to nurse the pup. In the case of Steller sea lions, females leave the rookery in the late afternoon or evening, feed overnight, and return to the rookery the following day to nurse the pup. On many rookeries females leave accompanied by the pup when it is several weeks to a couple months old and move to distant haul-out sites. Females may wean pups when 6 to 11 months of age, but some continue to nurse their young for 2 or more years, forgoing annual reproduction. Alternative terrestrial haul-out sites are used by juvenile animals during the breeding season and by all age and sex groups during the remainder of the year. Many rookery islands are not occupied during winter months. Their large breeding colonies and haul-out sites make them susceptible to human hunters on land. They have been identified in archaeological sites throughout the northeastern Pacific but are generally most abundant in sites in northerly, cooler waters (e.g., Lyman 2003). Archaeological Steller sea lion remains from the Aleutians have also been used to evaluate the role of climate forcing versus human predation for recent and ancient declines of the population, with these studies generally favoring climate forcing (Trites et al. 2007).

California sea lions are a relatively large, sexually size dimorphic otariid, with males averaging 225 cm and 325 kg and females 180 cm and 110 kg (Orr and Helm 1989). Often found on offshore rocks and secluded beaches, they range from the Tres Marianas Islands, Mexico, throughout the Sea of Cortez, and north to the Gulf of Alaska (Jefferson et al. 2008). They breed on islands in the Sea of Cortez, along the Pacific coast of Baja California, northward to the major breeding populations in the California Channel Islands and the Farallon Islands. Like Steller sea lions, they are regarded as nonmigratory, although some age and sex groups of California sea lions display lengthy seasonal movements (Riedman 1990) and feed on a variety of prey, including fishes and squids. The California sea lion may have dropped to as few as 1500 individuals following historic exploitation but have since recovered to about 240,000 animals (Jefferson et al. 2008; Carretta et al. 2007). DeLong and Melin (2002) noted that some 80,000 California sea lions currently breed on California’s San Miguel Island (and this population has continued to increase during this decade [DeLong, unpublished data]). The IUCN lists the California sea lion as of least concern, and they are regarded as within the Optimum Sustainable Population Level under the U.S. Marine Mammal Protection Act (Carretta et al. 2007).

California sea lions are polygynous and breed and pup on land in territorial breeding colonies that are highly susceptible to human predation and other activities. Female sea lions give birth to pups in May and June and alternate terrestrial nursing and multiday marine foraging trips for 6 to 11 months, when the pup is weaned. Thus females and pups are found on the rookery island all year. Some juvenile animals remain on haul-out sites on rookery islands all through the year, but some portion of the juvenile population migrate northward to central and northern California where they alternate marine foraging and terrestrial hauling activity on offshore rocks and islands; in recent times they have hauled out in urban areas such as Monterey Bay and San Francisco Bay. Adult males visit the rookery islands during the pupping and breeding season from May through July. Many adult males establish and maintain reproductive territories on rookeries, but a near-equal number of adult males appear to spend the breeding season hauled out on island beaches that are not rookeries. Following the breeding season, all adult males migrate northward to haul-out sites all along the coast from central California through British Columbia, Canada. California sea lions are fairly common in archaeological sites in California, especially in Late Holocene sites on the Channel Islands and southern California coast (Braje 2010; Hildebrandt and Jones 1992; Porcasi et al. 2000; Rick 2007; Walker et al. 2002).

Northern fur seals are also sexually size dimorphic, with males up to 210 cm in length and from 180 to 270 kg and females up to 150 cm and from 43 to 50 kg (Jefferson et al. 2008; Orr and Helm 1989). Fur seals are highly migratory, ranging from southern California around the northern Pacific Rim to Honshu, Japan. Adults breed on terrestrial rookeries in reproductive territories. Following a 4-to-5-month breeding season, they go to sea, with the majority of adults and most juveniles remaining at sea and feeding pelagically across the North Pacific until the following breeding season, when they again come ashore. Most juvenile animals from 4 months through 3 years of age remain at sea year round. In the fourth year of life, many of the animals come ashore for the first time since birth, females to breed and males to haul out, and begin developing the terrestrial skills needed to obtain and maintain reproductive territories. Most males are not successful in obtaining a territory until 8 to 10 years of age. Northern fur seals prey on a variety of fish and squid found on the continental shelf and over deep oceanic waters. Northern fur seals were heavily affected by historical human exploitation, with the population currently thought to be around 1,000,000 and declining. They are listed by the IUCN as vulnerable and as a depleted species under the Marine Mammal Protection Act (Jefferson et al. 2008; Carretta et al 2007).

A highly polygynous species, northern fur seals breed from mid-June to August. Northern fur seals breed today on isolated islands that are generally distant from humans, bears, and other predators (e.g., Commander, Pribilof, and Bogoslof Islands and San Miguel Island; see DeLong and Melin 2002). Females give birth to a single pup, are bred 6–7 days later, and begin to alternate multiday marine feeding trips and terrestrial nursing cycles, which continue until the pup is weaned at 4 to 5 months of age. Following weaning, females and pups go to sea, and females do not return until the next breeding season. Archaeological data from California, Washington, and elsewhere are interpreted by some to indicate that northern fur seals may have been more common prehistorically in mainland areas and may have even bred on some portions of the California and Washington mainland (see Etnier 2002a; Gifford-Gonzalez et al. 2005; Newsome et al. 2007). Alternatively, fur seals may have been harvested at sea in coastal waters by early humans using marine technology developed in parts of the eastern Pacific coast during the Holocene, and/or as sick or injured animals that washed ashore (see Gifford-Gonzales et al. 2005 for a discussion and Moss and Erlandson 1995 for discussion of technologies). The presence of northern fur seal bones, including pups in archaeological contexts, has prompted considerable debate among a variety of researchers as to whether these represent sick or injured animals that washed ashore, were animals taken at sea, or if fur seal breeding and migration patterns were dramatically different during the Late Holocene than the modern and historical era (see Gifford-Gonzalez et al. 2005). These debates are revisited in this volume.

Like other otariids, Guadalupe fur seals are sexually dimorphic, with females averaging 120 cm in length and 40 to 50 kg and males 180 cm in length and 160 to 170 kg (Belcher and Lee 2002). Guadalupe fur seals are also non-migratory, although they are known to disperse to the Channel Islands and other areas (Belcher and Lee 2002; DeLong and Melin 2002). Prior to the 19th century, Guadalupe fur seals ranged from San Miguel Island southward through Isla de Guadalupe, Islas San Benitos, and Isla Cedros, Baja California, Mexico (Rice 1998; Belcher and Lee 2002; Repenning et al, 1971). They currently breed only on Isla de Guadalupe and Islas San Benitos (Carretta et al. 2007), although a single pup was born on San Miguel Island in 1997 (Melin and DeLong 1999). Recent archaeological data from the Ozette site in northwestern Washington yielded the remains of several Guadalupe fur seals dated to the last 500 years, suggesting they once ranged considerably further to the north (Etnier 2002b). They generally feed on squid, bony fish, and crustaceans. Over 12,000 Guadalupe fur seals were thought to exist in 2003 (Gallo-Reynoso et al. 2005), and the IUCN currently lists the population as vulnerable and it is listed as threatened under the U.S. Endangered Species Act.

Guadalupe fur seals are polygynous and give birth to pups and breed on rocky beaches and in caves (Belcher and Lee 2002). Females give birth to a single pup in June and July and are bred several weeks later. They then alternate nursing the pup for 1 to 2 days and feeding at sea away from the rookery for several days until pups are weaned at 8 to 11 months of age. Guadalupe fur seal females are also very common in archaeological sites from the Late Holocene California Channel Islands (Braje 2010; Porcasi et al. 2000; Rick 2007; Rick et al. 2009; Walker et al. 2002), suggesting they were much more abundant prior to historical depletion.

PHOCIDS

Some 19 species of phocid are found around the world, with only two species ranging widely in the northeastern Pacific (Jefferson et al. 2008). The northern elephant seal is sexually dimorphic and the largest of all the North Pacific pinnipeds, with males up to 410 cm and 2300 kg and females 280 to 300 cm and 600 to 800 kg (Stewart and Huber 1993). Pushed to the brink of extinction in the 1800s, a few animals were identified on Isla de Guadalupe off Baja California, Mexico, in the late 1800s. The population has since recovered dramatically, with some 50,000 animals breeding on San Miguel Island alone (DeLong and Melin 2002) and in excess of 120,000 in U.S. waters (Carretta et al. 2009). They have low genetic diversity, probably resulting from the historical population collapse (Stewart and Huber 1993). Currently, they range widely in the North Pacific, foraging from the Gulf of Alaska and the Aleutians southward to the Oregon and California coast and the Channel Islands and Baja California, where they pup and breed. The IUCN lists the northern elephant seal as least concern (Jackson et al. 2008); they are not threatened or endangered under the ESA, and they might be approaching the Optimum Sustainable Population (OSP) (Carretta et al. 2007). They are a highly migratory species, preying on squid and fish. They are known to dive to 1000 meters or more and make two yearly migrations totaling at least 21,000 km (DeLong and Stewart 1991; Stewart and DeLong 1995).

Elephant seals breed on land in large reproductive territories. Pups are born in January and February, are nursed for about 30 days, and are weaned by the departure of the female following breeding. Pups then remain on the island for up to 3 months, gradually developing swimming skills, and finally go to sea not to return until they haul out to molt 1 year later. As is the case in all phocids, elephant seals spend the majority of the molt period, which lasts about 4 to 6 weeks, on land (or ice in the case of some of the ice seals). Although they are large and conspicuous marine mammals that breed and haul out on land, they are fairly rare in archaeological assemblages. They have been found in a limited number of sites in the northeastern Pacific primarily dated to the last 1500 years but usually occur in very low frequencies (Rick et al. 2010).

The harbor seal is a small phocid. Although males are generally larger than females, they are not sexually dimorphic and are about 150 to 190 cm and 60 to 150 kg (Jefferson et al. 2008; Orr and Helm 1989). Their geographic range includes islands and the coast in the North Pacific from Japan to central Baja California, and they are also present in the southern Bering Sea. Harbor seals rarely venture far from the water, and when on land they frighten easily when humans are near. They forage on fish, cephalopods, and crustaceans. Estimating harbor seal populations is difficult, but Jefferson et al. (2008) suggest that there are likely some 300,000 to 500,000 animals, with Carretta et al. (2007) estimating the California population at least 31,600 animals, the Oregon and Washington stock at around 22,380, with at least 12,844 in Washington’s inland waters. The Alaska population is estimated at 180,000 animals (Angliss and Allen 2009). The IUCN categorizes the harbor seal as a species of least concern (Jefferson et al. 2008), and they are not listed as endangered or threatened under the ESA (Carretta et al. 2007).

Like all the Pacific coastal pinnipeds, harbor seal females give birth to a single pup on land. They then nurse the pup for about 4 to 5 weeks before weaning. Harbor seals mate in the water from February to October and are promiscuous to weakly polygamous (Jefferson et al. 2008). Harbor seals do not migrate and may not move away from the rookery and haul-out areas, spending some portion of all weeks (in some cases days) of the year on land. These and other factors led Hildebrandt and Jones (1992) to call harbor seals and sea otters residential and later aquatic breeders (Jones et al. 2004), arguing that they would generally be much more difficult to acquire through hunting than otariids. Harbor seals are fairly common in northeastern Pacific archaeological sites but are rarely a dominant species (Lyman 2003; Porcasi et al. 2000; Walker et al. 2002). Harbor seals remain a valued resource to Alaska Natives and in excess of 2000 are harvested there each year (Angliss and Allen 2009).

SEA OTTER

The smallest of the North Pacific marine mammals, sea otters are members of the family Mustellidae, which includes some 67 species, only two of which are marine (Jefferson et al. 2008). There are two subspecies of sea otters that occur in the North Pacific archeological record, E.l. kenyoni is distributed from the western Aleutian Islands across the North Pacific and south currently to Washington. The second, E.l. nereis, is currently found only in central California but was prehistorically distributed from central Baja California north probably through at least Oregon (Rice 1998; Valentine et al. 2008; Wilson et al. 1991). Like the harbor seal, sea otters have limited sexual size dimorphism, with males averaging 126 to 145 cm in length and 21 to 45 kg and females 107 to 140 cm and 14 to 33 kg (Estes 1980). Sea otters spend most or all of their lives in the water. They are often solitary but can rest in groups and will only venture on land in very protected areas or when sea otter abundance is high (Estes 1980). They are generally nonmigratory, but seasonal movements of long distances have been documented. Sea otters were pushed to the brink of extinction during the fur trade and were extirpated in numerous areas. Prior to the fur trade, they appear to have ranged from Baja California, around the North Pacific Rim, and into Hokkaido, Japan (Estes 1980). According to the IUCN, the sea otter is currently endangered throughout its range. The California sea otter and the Southwest Alaska otter populations are listed as threatened under the ESA. The remaining two Alaska stocks (Southeast and South Central) and the Washington stock are not listed.

They forage on invertebrates, especially sea urchins, mussels, crab, and abalones, as well as on fish in some areas (Estes 1980). They are a fundamental component of kelp forest ecosystems and help regulate sea urchin and other grazing invertebrate populations. During the fur trade and in modern times, the decimation of sea otters allowed sea urchin populations to skyrocket, resulting in kelp barrens in numerous areas (Simenstad et al. 1978; Steneck et al. 2002). Identified in San Miguel Island archaeological sites as old as 9000 years (Erlandson et al. 2005), sea otters are often abundant in Aleutian, Californian, and other archaeological sites (see Corbett et al. 2008). Sea otters are polygynous and mate and breed in the water. Although sea otters commonly haul out on beaches in Alaska, it is generally considered by archeologists that sea otters would have likely been captured in water and, compared to many pinnipeds and sea cows, would have been difficult prey (Hildebrandt and Jones 1992). Simenstad et al. (1978), Corbett et al. (2008), and Erlandson et al. (2005) have suggested that prehistoric reductions in sea otters from ancient human hunting, albeit on different scales than the fur and oil trade, may have resulted in significant changes in ancient nearshore kelp forest ecosystems (see also Jones et al. this volume).

HISTORICAL TRANSFORMATIONS

All the northeastern Pacific marine mammal species described in this chapter underwent dramatic declines during the 18th and 19th centuries (Ellis 2003). As human hunters moved to new areas of the globe to acquire these animals for the commercial fur trade, populations were dramatically reduced, pushed to the brink of extinction or to local extirpation, or went completely extinct in the case of Steller’s sea cows. Some of this depletion was extremely rapid, with the sea cow apparently extinct just a few decades after its discovery by Europeans.

Bodkin (2000) estimates that between 500,000 and 900,000 sea otters were killed from 1742, when commercial harvest began, until 1910, when a final, unsuccessful hunt was staged. Historical commercial hunting of seals and cetaceans began even earlier than that of sea otters. Intensive harvest of whales began at least in the 16th century and continued well into the 20th century. The oil of many whales and various dolphins has been a prized commodity for a number of household and industrial purposes, including the production of lamp oil, soap, leather dressing, steelmaking, and textile sizing (Ellis 2003:237). The historic decimation of cetacean populations is staggering, with thousands killed each year for at least four centuries and commercial harvest of many whale and dolphin species continuing today.

Fur seals and sea lions have endured a similar history. Throughout North Pacific waters, Guadalupe fur seals, northern fur seals, California sea lions, and Steller sea lions were all slaughtered by the thousands for their fur, blubber, and trimmings beginning in the early to mid-1700s (Ellis 2003:161–178). The trimmings trade was especially wasteful, targeting only the genitals of bull seals for medicinal and aphrodisiacal purposes, the gall bladder for a type of medicine, and the whiskers for opium pipe cleaners or toothpicks (Busch 1985:201–202). Northern elephant seals, lacking the luxurious pelts of the fur seal, were targeted for their thick blubber, which was boiled down into oil.

This historic blitzkrieg dramatically altered marine mammal populations in the northeastern Pacific and beyond. Nearly every species that survived suffered significant historic population size reductions and, in some cases, decreases in genetic variability (genetic bottlenecks). Mitochondrial DNA (mtDNA) studies, for example, have demonstrated that all extant populations of sea otters have suffered at least one population bottleneck (Riedman and Estes 1990) and show low levels of genetic variability (Bodkin et al. 1999; Lidicker and McCollum 1997). A similar pattern of low genetic diversity exists among northern elephant seals and Guadalupe fur seals (Bernardi et al. 1998; Bonnell and Selander 1974), especially when compared to DNA of prehistoric specimens (Hoelzel et al. 2002; Weber et al. 2004).

In 1972, the Marine Mammal Protection Act was passed, providing protection to all marine mammals in U.S. waters regardless of their status. The result has been a recovery of many species to levels that may be comparable to those prior to intensive historical predation (Jefferson et al. 2008), but the dearth of historical records prior to the mid 19th century makes archaeology one of the few sources of data for reconstructing prehistoric pinniped biogeography. Northern elephant seals and California sea lions have fared particularly well, with Guadalupe fur seals also increasing in population. In some parts of their range, Steller sea lions are endangered and have undergone declines throughout the southern part of their range in recent decades and have stopped breeding on San Miguel Island completely (DeLong and Melin 2002; Trites and Donnelly 2003), but they have been increasing from Oregon to southeast Alaska, where they are listed as threatened, and in Canada they are listed as a species of special concern. The Northern fur seal population recovered to nearly 2 million animals after reaching a low point in 1910. But since 1970 the population has declined by half due to unknown causes. Finally, sea otters are absent from much of their original range, have undergone population declines in southwestern Alaska, and translocations have been met with varying degrees of success (see Hatfield 2005).

ARCHAEOLOGICAL IMPLICATIONS AND VOLUME OVERVIEW

These historical transformations, including dramatic population declines, recoveries, and rebounds, range expansions and contractions, and other shifts provide an important backdrop for interpreting the archaeological record of pinnipeds, sea otters, and other marine mammals in the northeastern Pacific. Archaeology is poised to provide crucial information on long-term ecology, biogeography, and human interactions with pinnipeds and sea otters. As Monks (2005b) noted, however, compared to other organisms (i.e., terrestrial mammals) marine mammals have received relatively limited attention from zooarchaeologists. In the case of pinnipeds and sea otters, this appears to be changing, especially in the northeastern Pacific, as several studies since the 1990s have provided archaeological information on pinnipeds and otters (e.g., Crockford and Frederick 2007; Etnier 2002a, 2007; Gifford-Gonzalez et al. 2005; Hildebrandt and Jones 1992; Jones and Hildebrandt 1995; Lyman 1995, 2003; Moss et al. 2006; Newsome et al. 2007; Rick et al. 2009, 2010).

With each new study it is clear that much remains to be learned about pinnipeds and sea otters in the more distant past, especially as some archaeological data appear to be at odds with modern ecological data or at least raise questions about modern pinniped distributions and behavior. Data on northern fur seals from the northeastern Pacific, for example, have been used to support the hypothesis that breeding colonies of northern fur seals may have existed on the mainland of central California, a pattern that, if correct, is dramatically different from the present or historical situation (Gifford-Gonzalez et al. 2005; Newsome et al. 2007). Work at the Ozette site in Washington, moreover, documented Guadalupe fur seals in deposits dated to the last 500 years, showing a much larger range than is known from the modern era (Etnier 2002b). Hunting of sea otters in the Aleutians and California Channel Islands by ancient Native peoples also suggests that human hunters may have caused localized impacts on kelp forests in the distant past (Corbett et al. 2008; Erlandson et al. 2005; Simenstad et al. 1978).

The chapters in this volume deepen our knowledge by providing information on ancient pinnipeds, sea otters, and sea cows throughout the northeastern Pacific. In total, the volume comprises the most comprehensive, interdisciplinary study on the archaeology of pinnipeds and sea otters from this region and serves as a model for other historical ecological studies elsewhere in the world.

Thirteen chapters from the Aleutian Islands to the southern California Channel Islands cover a variety of different species and draw on diverse methodological perspectives to yield empirical and theoretical insights. In Chapter 2, Lyman provides a comprehensive analysis of the history of paleoecological research on northeastern Pacific pinnipeds and sea otters. After this chapter, ten regional case studies from the northeastern Pacific are presented. In Chapter 3, Hill explores human exploitation of walrus in the far North Pacific along the Bering Strait. In Chapter 4, Crockford and Frederick present their research on fur seal breeding patterns and changing sea ice and other environmental variables in Alaska. This is followed by Betts, Maschner, and Lech’s results (Chapter 5 and Chapter 6) from their research in the Aleutians (Betts et al. and Lech et al., respectively). In Chapter 7, McKechnie and Wigen summarize the history of pinniped exploitation on the coast of southern British Columbia. We then move to the Oregon and Washington coasts, where Moss and Losey (Chapter 8) analyze the regional archaeological record of pinnipeds and sea otters. Whitaker and Hildebrandt (Chapter 9) examine aspects of the northern California record of pinniped hunting and human prestige economies. In Chapter 10, Gifford-Gonzalez provides detailed information on her long-term research on fur seals in central California. Jones et al. (Chapter 11) then provide insight into the long-term dynamics of human hunting of sea otters in central California, including ancient DNA and stable isotope data. This is followed by Braje et al.’s (Chapter 12) overview of pinniped and sea otter hunting on the California Channel Islands. Finally, Braje and Rick provide an analysis, critique, and suggestions for further research in Chapter 13.

ACKNOWLEDGMENTS

Discussions with Jon Erlandson, Mike Etnier, Mike Glassow, Bill Hildebrandt, Terry Jones, Doug Kennett, Sharon Melin, Madonna Moss, Seth Newsome, Tony Orr, Tom Wake, Phil Walker, and others have greatly increased our understanding of the archaeology and biology of pinnipeds and sea otters. We thank all the contributors for their efforts in meeting our deadlines, writing insightful chapters, and helping bring this volume to fruition. Mark Raab and Andrew Trites provided important comments that greatly improved this chapter and the rest of the volume.

REFERENCES CITED

Alvard, M. A.

1998 Evolutionary Ecology and Resource Conservation. Evolutionary Anthropology 7:62–74.

Angliss, R. P., and B. M. Allen

2009 Alaska Marine Mammal Stock Assessments, 2008. NOAA Technical Memorandum NMFS-AFSC-193.

Bailey, G.

2004 World Prehistory from the Margins: The Role of Coastlines in Human Evolution. Journal of Interdisciplinary Studies in History and Archaeology 1:39–50.

Belcher, R. L., and T. E. Lee, Jr.

2002 Arctocephalus townsendii. Mammalian Species 700: 1–5.

Bernardi, G., S. R. Fain, J. P. Gallo-Reynoso, A. L. Figeuroa-Carranza, B. J. Le Boeuf

1998 Genetic variability in Guadalupe fur seals. Journal of Heredity 89:301–305.

Berta, A., J. L. Sumich, and K. M. Kovacs

2005 Marine Mammals: Evolutionary Biology. Second Edition. Academic Press, San Diego.

Bodkin, J. L.

2000 Sea Otters. Alaska Geographic 27(2):74–92.

Bodkin, J. L., B. E. Ballachey, M. A. Cronin, K. T. Scribner

1999 Population Demographics and Genetic Diversity in Remnant and Translocated Populations of Sea Otters. Conservation Biology 13:1378–1385.

Bonnell, M. L., and R. K. Selander

1974 Elephant Seals: Genetic Variation and Near Extinction. Science 184:908–909.

Braje, T. J.

2010 Modern Oceans, Ancient Sites: Archaeology and Marine Conservation on San Miguel Island, California. University of Utah Press, Salt Lake City.

Broughton, J. M.

1994 Declines in Mammalian Foraging Efficiency during the Late Holocene San Francisco Bay, California. Journal of Anthropological Archaeology 13:371–401.

1999 Resource Depression and Intensification during the Late Holocene, San Francisco Bay: Evidence from the Emeryville Shellmound Vertebrate Fauna. University of California Anthropological Records 32.

Burton, R. K., D. Gifford-Gonzalez, J. J. Snodgrass, and P. L. Koch

2002 Isotopic Tracking of Prehistoric Pinniped Foraging and Distribution along the Central California Coast: Preliminary Results. International Journal of Osteoarchaeology 12:4–11.

Burton, R. K., J. J. Snodgrass, D. Gifford-Gonzalez, T. Guilderson, T. Brown, and P. L..Koch

2001 Holocene Changes in the Ecology of Northern Fur Seals: Insights from Stable Isotopes and Archaeofauna. Oecologia 128:107–115.

Busch, B. C.

1985 The War against the Seals: A History of the North American Seal Fishery. Kingston, Ontario: McGill-Queen’s University Press.

Carretta, J. V., K. A. Forney, M. M. Muto, J. Barlow, J. Baker, B. Hanson, and M. S. Lowry

2007 U.S. Pacific Marine Mammal Stock Assessments: 2006. U.S.