Archaeology, Marine Ecology, and Human Impacts on … ocean crisis have been hampered by ......

overing more than 70 percent ofour blue planet, the oceans dominate the

earth in a variety of ways. With an averagedepth of almost 4 km, they provide over 99 per-cent of the habitable space for life on earth(Woodard 2000:31). As human populationshave grown exponentially over the past century,and with 60 percent of the world’s populationliving within 100 km of the coast, many havelooked to the oceans as a source of hope andprotein to feed the masses. Once thought to benearly inexhaustible, many global fisherieshave collapsed or are severely depleted (Jacksonet al. 2001; Pauly et al. 2002; Roberts 2002;Worm et al. 2006). Pollution, habitat loss,global warming, and the introduction of exoticspecies also take an increasing toll on coastaland pelagic ecosystems (see Carlton et al. 1999;Earle 1995; Ellis 2003; Vitousek et al. 1997:495;Woodard 2000). We are only beginning tounderstand the larger ecological consequencesof such impacts, including the wholesale col-lapse of many coral reef, kelp forest, estuarine,arctic, benthic, and other ecosystems—founda-tions of marine productivity that have nurturedhuman societies for thousands of years. Theseimpacts are now global in scale, but humans

have had the heaviest impact on nearshore andcoastal areas (0–50 m in depth), substantialimpacts on deeper continental shelf habitats(50–200 m), and comparatively less impact onthe deeper oceans (Steele 1998).

In the last few years, two national commis-sions have issued reports concluding that theworld’s oceans and fisheries are in a state of cri-sis (Pew Oceans Commission 2003; U.S. Com-mission on Ocean Policy 2004). The manage-ment of fisheries and our understanding of thebroader ocean crisis have been hampered bythe shallow historical focus of policy makersand resource managers, who have based manydecisions on ecological observations that span10, 20, or 30 years, or on historic catch recordsthat rarely span more than a few additionaldecades. Just over a decade ago, Daniel Pauly(1995) referred to this problem as the “shiftingbaselines syndrome,” where fisheries managersuse recent historical baselines to manage fish-eries that are depleted or collapsed. Such recenthistorical baselines are often fundamentallyflawed because they fail to account for the abun-dance of key species prior to heavy fishing orhunting by indigenous peoples or early com-mercial harvests (Dayton et al. 1998; Jackson

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Archaeology, Marine Ecology, and HumanImpacts on Marine Environments

Jon M. Erlandson and Torben C. Rick

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et al. 2001). Roman and Palumbi (2003) ana-lyzed the DNA of living whales, for instance,and suggested that the original population sizesfor some whale species was 10 or more timeslarger than estimated by the historical recordscurrently used as baselines for restoring andconserving whale populations. A growing num-ber of marine scientists are now calling for fun-damental changes in the management ofmarine fisheries and ecosystems, includingmuch deeper historical analyses that incorpo-rate archaeological and other data sets into thedevelopment of better fisheries managementplans, ecosystem restoration efforts, and a sus-tainable oceans policy.

An important step forward in this effort wasa 2001 article in Science called “Historical Over-fishing and the Recent Collapse of MarineEcosystems,” named by Discover magazine asthe top science story of the year. In it, Jacksonet al. (2001) argued that human impacts onmarine fisheries began relatively early, but theyalso recognized that human fishing has evolvedthrough three general (and often overlapping)historical and geographic stages: (1) aboriginalfisheries confined to “subsistence exploitationof nearshore coastal ecosystems” with “rela-tively simple watercraft and extractive technolo-gies”; (2) colonial exploitation of coastal andcontinental shelf ecosystems controlled by“mercantile powers incorporating distantresources into a developing market economy”;and (3) a global stage marked by “more intenseand geographically pervasive exploitation ofcoastal, shelf, and oceanic fisheries integratedinto global patterns of resource consumption.”Within this framework, human impacts onmarine fisheries and ecosystems have acceler-ated through time and expanded geographicallyas human populations grew, extraction and dis-tribution technologies improved, and increas-ingly global markets emerged. Here, we arguethat management strategies for fisheries andother ocean resources need to consider not justshifting baselines and the historical ecology ofmarine ecosystems, but the “shifting timelines”that emerge from the knowledge that the history

of boats, maritime migrations, and marine fish-ing and hunting developed considerably earlierthan previously believed in many parts of theworld (Erlandson and Fitzpatrick 2006).

Like most archaeologists, we have longthought of ourselves as pretty interdisciplinaryguys, with a relatively good grasp on the geol-ogy, biology, and ecology of Pacific Coast ecosys-tems. A few years ago, one of us (JME) wasasked to join a working group (Long-Term Eco-logical Records of Marine Ecosystems) at theNational Center for Ecological Analysis andSynthesis (NCEAS). Chaired by Jeremy Jack-son, this group of 25 marine scientists met peri-odically for several years to discuss, debate, andreconstruct regional and global patterns in thehistorical development of human impacts onmarine ecosystems. Several members of thatgroup—Bruce Bourque, Debbie Corbett, JimEstes, Mike Graham, and Bob Steneck—areparticipating in one way or another in this vol-ume. After joining the NCEAS group, Erland-son learned that his knowledge of biologicaland ecological issues was as broad as a river butshallow as a thin sheet of water. It also becameclear that most ecologists think of “long-term”ecological records as spanning two or threedecades of regular scientific observation, some-times supplemented with a few decades moreof historical catch data. When the archaeolo-gists in the group described coastal archaeolog-ical records spanning millennia in California,the Aleutians, and the Gulf of Maine, themarine ecologists were amazed at their poten-tial. When the marine ecologists described thestructure and dynamics of kelp forest ecosys-tems in each area, it was the archaeologists’turn to be astonished. What followed was aremarkable series of meetings with these andother colleagues examining the historical ecol-ogy of coastal ecosystems and the changingnature of human impacts to such systemsthrough time.

Growing out of these interdisciplinary ses-sions, and several years of related research theyinspired, we also gained clearer insight intojust how much coastal archaeology has to offer

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current research, debates, and policy related tomarine conservation and restoration, fisheriesmanagement, and other crucial ocean issues.As Lyman and Cannon (2004) argued, theapplication of archaeological data to currentproblems in conservation biology raises a num-ber of thorny issues, but it also represents atremendous opportunity for archaeologists tobetter meet the crucial test of relevance formodern society. Already widely perceived in thereal world as an interesting but esoteric field,archaeologists cannot afford to miss opportuni-ties to prove our relevance to current and press-ing issues, not if we hope to receive continuedfunding for our work and support for the pro-tection of archaeological sites.

THE ARCHAEOLOGY OF HUMAN IMPACTS

The archaeological record encodes hundredsof situations in which societies were able todevelop long-term sustainable relationshipswith their environments, and thousands of sit-uations in which the relationships were short-lived and mutually destructive. The archaeo-logical record is “strewn with the wrecks” ofcommunities that obviously had not learned tocope with their environment in a sustainablemanner or had found a sustainable path, butveered from it only to face self-destruction.

(Redman 1999:4–5)

In recent decades, there has been tremen-dous interest in the archaeological study ofhuman impacts on ancient ecosystems, includ-ing the role early hunter-gatherers and agricul-turalists played in the extinction of animalspecies, major habitat alterations, and the col-lapse of complex cultures (e.g., Grayson 2001;Grayson and Meltzer 2001; Martin 1967;Martin and Klein 1984; Redman 1999;Redman et al. 2004). Far from “living in har-mony” with their environments—if any scien-tists ever actually believed this notion—thearrival of anatomically modern humans (Homosapiens sapiens) in newly colonized lands oftenappears to be associated with significant habitatchanges and accelerated rates of extinction. AsGrayson (1991, 2001; Grayson and Meltzer

2003) and others have shown, it can be difficultto prove that human hunting was the primarycause of many animal extinctions. Nonetheless,cases for a significant human contribution toextinction events or other environmentalimpacts have been made for late PleistoceneAustralia (Flannery 1994; Miller et al. 1999;Roberts et al. 2001), the Americas during theterminal Pleistocene (Alroy 2001; Martin2002), some Caribbean Islands in the EarlyHolocene (Morgan and Woods 1986; Steadmanet al. 2005), many Pacific Islands and Madagas-car during the Late Holocene (Anderson 1984,1989; Kirch and Hunt 1997; Simmons 1999;Steadman 1995, 2006), and other areas aroundthe world. It is not always clear if such changesresulted from human hunting, forest clearanceor intentional burning of landscapes, the intro-duction of exotic animals (dogs, pigs, rats, etc.)and the diseases they carried, or a combinationof factors. What is clear, however, is that the ini-tial arrival of behaviorally modern and techno-logically sophisticated H. s. sapiens in any givenregion appears to have posed significant prob-lems for many endemic species, especiallywhere such species had not been subjected tohominid predation before.

Although both continental and island land-scapes have played important roles in studyingthe impacts of early humans, discussions ofhuman-induced extinctions are limited almostexclusively to vertebrate species that live, nest,feed, or breed on land. In cataloging a globalbestiary of large animals potentially driven toextinction by our ancestors, Martin (2002)listed scores of terrestrial genera, but no marineor aquatic species. As Martin (2002:1) noted:“Whatever caused large animal extinctions onland, had no impact on large mammals in theoceans.” The differential patterns of prehistoriclarge animal extinctions in terrestrial versusaquatic ecosystems raise two very interestingquestions that require further exploration: (1)why did the expansion of anatomically modernhumans differentially affect terrestrial versusmarine species?; and (2) does the lack of docu-mented extinctions in marine ecosystems mean

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that human impacts on those ecosystems wereabsent or severely limited until very recently?

SHIFTING TIMELINES

In the past, the first question was easily answeredwith traditional anthropological theory, whichheld that hominids did not intensively exploitmarine or aquatic resources until relatively latein human history—between about 15,000 and5,000 years ago (e.g., Osborn 1977; Washburnand Lancaster 1968; Yesner 1987). Boats andother relatively sophisticated maritime technolo-gies were also viewed as relatively recent devel-opments, suggesting that most island archipela-goes were not colonized until relatively recently.The supposedly late shift toward intensiveaquatic adaptations, in which marine resourceswere largely ignored for 99 percent of humanhistory, was often explained as a shift toward“marginal” aquatic resources after the “optimal”large land mammals were hunted to extinctionor severely depleted. If humans developedintensive marine fisheries relatively late in pre-history, then perhaps the dearth of aquaticextinctions is simply due to the differentialantiquity of terrestrial hunting versus aquatichunting and fishing.

The problem with this scenario, of course, isthat we live in an interglacial period of high sealevels unmatched in the last 120,000 years. Asglobal sea levels rose over 100 m between 20,000and 5,000 years ago, the coastlines of the worldchanged dramatically. Most coastlines moved lat-erally tens or even hundreds of kilometers, mean-ing that most sites located along modern coast-lines were far from marine habitats during thelate Pleistocene (see Parkington 1981). Coastalerosion also destroyed, dispersed, or severelydamaged most coastal sites submerged duringthis marine transgression (Erlandson 2001;Erlandson and Fitzpatrick 2006). Unfortunately,these dramatic changes in coastal geographycoincide with the later development and spreadof anatomically modern humans (H. s, sapiens),insuring that records of early coastal adaptationsor migrations are severely limited.

Despite such problems, recent research in aseries of African sites of Last Interglacial age,other sites in coastal zones where steep bathym-etry limited lateral shoreline movements, islandsthat humans could have colonized only by boat,and freshwater aquatic localities has dramaticallyaltered our view of the antiquity of aquatic adap-tations, maritime migrations, and human fish-ing and hunting in marine ecosystems. Dozensof coastal Middle Stone Age sites in southernAfrica appear to contain evidence for the use ofshellfish, marine mammals, seabirds, and evenfish by anatomically modern humans betweenabout 125,000 and 40,000 years ago (e.g., Brinkand Deacon 1982; Henshilwood and Sealy 1997;Klein et al. 2004; Marean et al. 2004; Singer andWymer 1982). Barbed bone harpoons fromKatanda in Zaire suggest that sophisticatedfreshwater fishing technologies may have existedby 80,000 to 90,000 years ago (Yellen et al.1995). The Pleistocene peopling of Australia andwestern Melanesia by maritime migrationsthrough island Southeast Asia between roughly60,000 and 35,000 years ago (see Allen et al.1989; Clark 1991; Wickler and Spriggs 1988)suggests that our ancestors may have dispersedout of Africa by land and by sea, some of themfollowing the coastlines of southern Asia(Erlandson 2001, 2002; Stringer 2000). The col-onization of the Ryuku Islands and evidence forthe use of boats in Japan 35,000 to 25,000 yearsago suggests that early maritime peoples hadadapted to the relatively cool waters of the North-west Pacific during the Last Glacial. The settle-ment of California’s Channel Islands by mar-itime peoples as much as 13,000 to 12,000 yearsago (Erlandson et al. 1996; Johnson et al. 2002;Rick et al. 2001, 2005), as well as coastal shellmiddens on the Andean coast more than 11,000years old (Keefer et al. 1998; Richardson 1998;Sandweiss et al. 1998), also demonstrates an ear-lier and more sophisticated use of maritime oraquatic technologies than previously believedand may support early coastal colonization mod-els. These data, along with the terminal Pleis-tocene expansion of maritime peoples intorecently deglaciated coastal regions of Scandinavia,




the Early Holocene settlement of someCaribbean Islands, and the later but equallyamazing maritime migrations of Austronesianand Polynesian peoples allow us to view thedevelopment of diversified coastal and aquaticeconomies around the world as the outgrowth ofthe origins and expansion of intellectually andtechnologically sophisticated anatomically mod-ern humans in Africa some 150,000 years ago.

The early emergence of maritime peoples inmany parts of the world also suggests that it istime to reexamine the archaeological evidencefor human impacts in coastal environments. Ifhumans have been gathering, hunting, and fish-ing in some marine ecosystems much longerthan previously believed, then a relatively recentdevelopment of coastal economies cannotexplain the lack of human-induced extinctionsin those marine environments. With greateramounts of time for coastal peoples to expandtheir populations, increasing evidence for theearly development of aquatic and maritime tech-nologies, and a deeper history of colonizingmany of the less remote island arcs around theworld, we should expect to find earlier and moreextensive evidence for prehistoric humanimpacts to coastal and marine ecosystems thanpreviously believed possible.

LESSONS FROM THE PAST:

OVEREXPLOITATION, CONSERVATION,

AND SUSTAINABLE ECONOMIES

This brings us back to the question of whetherthe dearth of prehistoric extinctions in marineecosystems implies a lack of significant humanimpacts. By now, the answer to this questionshould be obvious. We clearly believe that thelimited evidence for human involvement inprehistoric aquatic extinctions should not beconsidered a lack of substantial impacts onancient marine, estuarine, and freshwaterspecies or ecosystems. In fact, a variety of evi-dence has been marshaled for a significantimpact of early human predation on the size,distribution, or population structure of aquaticspecies, including shellfish, fish, and some seamammals (see, among many others, Erlandsonet al. 2005; Hildebrandt and Jones 1992; Kleinet al. 2004; Reitz 2004; Simenstad et al. 1978;Steneck et al. 2004). The nature and extent ofsuch impacts remain to be documented in vari-ous areas around the world, however; and the grow-ing collaboration between coastal archaeologists,marine ecologists, and other scientists is develop-ing new methods for recognizing and measuringthe nature of those impacts (Figure 1.1).


FIGURE 1.1. Middle Holocene red abalone midden (SNI-161) eroding out of sand dune onnorthwestern San Nicolas Island (photo by René Vellanoweth).



Ancient humans did not live in completeharmony with their natural environments—atleast not for long. By definition, at least for ourpurposes, all humans affect their environment,and large human populations generally havelarger ecological impacts. Identifying archaeo-logical evidence for such impacts, however, isnot necessarily the same as demonstrating thatsome human societies never developed conser-vation measures or sustainable economies. Ifancient peoples never learned from their mis-takes and developed effective conservationstrategies, there may be little to be learned fromstudying the past. While it may be true, as Kay(2002:259–260) has argued, that it is conde-scending and morally indefensible to claim thatindigenous peoples were not capable of signifi-cant environmental impacts, it would beequally condescending to suggest that suchpeople were incapable of recognizing the eco-logical impacts they had or developing practicesthat encouraged conservation or sustainableyields. As archaeologists and anthropologists,we find it difficult to believe that ecologicalawareness and conservation strategies aresolely the province of literate or modern humansocieties.

Although some of our participants maytouch on such issues, we are not particularlyinterested in debating theoretical stances aboutwhether ancient peoples engaged in conserva-tion, sustainable practices, or ecologicallysound management principles. We have fol-lowed this debate closely, particularly as it hasplayed out in relation to Native North Ameri-cans (see, e.g., Alvard 1998; Grayson 2001;Guthrie 1971; Hunn et al. 2003; Kay andSimmons 2002; Krech 1999). Such issues canbe quite difficult to address using fragmentaryarchaeological data, and some of the rhetorichas been unnecessarily polarized and politi-cized. Native Americans, for instance, are vari-ously portrayed as having either widespreadcultural systems for conserving naturalresources, or virtually no effective conservationstrategies, with little middle ground. Such char-acterizations ignore the wide range of behaviors

that might be expressed by a succession of indi-viduals or groups within a single region overlong stretches of archaeological time.

Over more than 10,000 years of NativeAmerican occupation along the California Coast,for instance, there is every reason to expect tofind evidence for a wide range of harvest strate-gies, from overexploitation when resources areabundant, to more conservative practices whenkey resources became depleted. This is clearlythe case with historical fishing strategies—where regulation is generally limited or absentuntil a fishery is significantly depleted. Nor is itcorrect to conclude that indigenous harvesting ofsmall abalones or female seals or pups—forbid-den by most historical regulations—is necessar-ily the antithesis of conservation or sustainablepractices (see Porcasi et al. 2000; Raab 1992).Historical regulations were developed inresponse to specific harvest levels or practicesthat may not have applied to or been appropriatefor prehistoric peoples. Relatively small hunter-gatherer populations might regularly harvest alimited number of female, juvenile, and infantseals from a large rookery, for instance, withouta measurable decline in the local seal population.Under such demographic contexts, the huntingof female seals or their pups may have no bear-ing on the long-term sustainability of such prac-tices. As populations grow, however, the impacton these resources will inevitably be moresevere, perhaps causing the relocation of rook-eries and possibly greater impacts on sea mam-mal population structure.

We are not arguing that prehistoric peoplesdid not cause resource depression or alter thestructure of local ecosystems; in coastal zonesaround the world the archaeological evidence isoverwhelming that they often did (see Ander-son 1983; Broughton 1999; Butler 2000, 2001;Grayson 2001; Mannino and Thomas 2002;Nagaoka 2002). Yet the widespread evidencefor localized resource depression does not nec-essarily signal a complete lack of conservationpractices or sustainable economies amongsmall-scale societies. As with swidden agricul-ture under low population densities, shifting




residence patterns can cause the serial deple-tion of marine resources within local foragingterritories without a long-term alteration of thelarger ecosystem. In such cases, local resourcedepletion combined with a pattern of “shiftingsedentism” might be part of a sustainable set-tlement and economic strategy that could spanhundreds or even thousands of years.

As human populations fill their physical andsocial landscapes, of course, residential mobil-ity can be constrained by neighboring groups.With the filling of spatial niches and the coales-cence of foraging territories (“territorial cir-cumscription”) caused by human demographicexpansion, impacts in local foraging territoriesmay also coalesce into a regional depression ofresources and increasingly anthropogenic land-scapes and seascapes. It is here that archaeo-logical investigations for the earliest evidence ofsignificant regional human impacts to marineecosystems are likely to be most fruitful. At thesame time, such serious ecological impactsmay sometimes have led to the development ofsocial mechanisms that more effectively man-aged human harvest practices to encourage sus-tainable yields. Thus, it is conceivable the wide-spread resource depression, which some haveargued was typical of much of Native NorthAmerica prior to European contact (see Kay andSimmons 2002), gave rise to the conservation-oriented ecological management principles thatmany Native American tribes espoused afterEuropean contact—beliefs reinforced by thecommercial decimation of many animal popu-lations by rapacious colonial exploitation prac-tices under European and Euroamericanregimes (see Ellis 2003; Mowatt 1984).

In our view, recent evolutionary theory oftenportrays individual humans as overly preoccu-pied with personal gain and reproductive suc-cess, ignoring the fact that human survival andsuccess has most often been accomplished ingroup settings where people may maximize theirsuccess by adhering to communal decisions thatbenefit the larger group (see Ehrlich 2000:310).In human groups, elaborate cultural mecha-nisms (e.g., shame, ostracism, banishment, and

death) are developed to control or punish thosewho unacceptably enrich themselves at theexpense of the common good. Such strictures,imperfect as they were and are, operated bothwithin and between social groups. The riverinepeoples of the Pacific Northwest who blockedstreams with weirs each year to harvest prodi-gious amounts of salmon knew, for instance,that blocking all the salmon from ascending thestream would have disastrous consequences forfuture fish runs, for their upstream neighbors,and ultimately for their own peace and prosper-ity. In such cases, the interests of individualtribal members and their larger social groupwere virtually inseparable from ecologically sus-tainable practices. This is not to suggest thatthere were not many difficult lessons learned inthe long evolution of subsistence strategies andsocial relationships among such tribes.

Ultimately, suggesting that conservation didnot take place in nonliterate societies impliesthat we have little to learn from the environmen-tal relationships of smaller-scale cultures.Archaeological and historical records indicatethat many human groups were incapable of sur-mounting the problems caused by their environ-mental impacts, while others were able to adjusttheir strategies (see Diamond 2005; Redman1999). In the past, humans were confrontedwith countless environmental challenges—someof them of their own making—and responded ina variety of ways, both effectively and ineffec-tively. Learning what worked for those ancientpeoples and what did not holds valuable lessonsfor us today as we strive to more effectively man-age the environmental impacts of our species onboth land and sea. Human impacts may beinevitable, but long-term environmental catas-trophe and ecosystem collapse are not (see Kirch1997; Redman 1999).

MEASURING HUMAN IMPACTS

TO MARINE ECOSYSTEMS

In the absence of numerous extinctions ofmarine species linked to prehistoric human colonization, how do we recognize human




impacts to ancient marine ecosystems? Otherthan the standard predictors and proxies of popu-lation growth or intensification, how can we usedata from coastal archaeological sites to identifysignificant human impacts in marine environ-ments? How do we compare archaeological datato historical and ecological data that are often col-lected in very different spatial and temporalscales? The answers to such questions are com-plex and, in some cases, not fully worked out.There are some general methods archaeologistsand marine scientists have used, however, thatprovide insights into the nature of human inter-actions with marine ecosystems over long periodsof time. At this point, any methodology for meas-uring human impacts across prehistoric, historic,and recent times must be considered a work inprogress, since historical ecology is a very youngdiscipline and interaction between archaeologistsand marine scientists is still relatively limited.

Obviously, one of the first and most impor-tant issues is to differentiate natural (nonhu-man) variations in marine ecosystems fromthose caused by humans (Redman 1999; Reitzand Wing 1999:252). On the ecological side ofthings, there are few if any marine ecosystemsaround the world where we have a comprehen-sive understanding of the historical ecologywith any real time depth. Since careful, “long-term” ecological monitoring records rarely spanmore than a few decades, we do not yet knowthe full extent of cyclical fluctuations in mostecosystems that operate on decadal scales orlonger. It is only relatively recently, for example,that the notion of decadal regime shifts or thedramatic and far-reaching climatic and oceanicpatterns involved in El Niño/La Niña cycleshave been fully recognized, and their historicalparameters are still being defined. It is alsoincreasingly clear that the historical range andbehaviors of many marine species havechanged significantly as their populations weredevastated by early historical exploitation and,in some cases, have rapidly expanded underprotective regulations or legislation. Knowledgeof the geographic range and behavior of marinemammals along the Pacific Coast of North

America—which ecologists and archaeologistshave often extrapolated uncritically into thepast—is rapidly changing, for instance, as vari-ous species continue to expand and adjust todynamic oceanic conditions and the alterationof marine ecosystems caused by overfishing,habitat changes, and other human impacts (seeBurton et al. 2001, 2002; DeLong and Melin1999; Estes et al. 1998; Etnier 2004).

Marine ecologists desperately need archaeo-logical colleagues to help expand their historicalhorizons, and coastal archaeologists desperatelyneed marine ecologists to help interpret the eco-logical implications of our data and understandthe broader import of our work. What are the eco-logical implications of changes in faunal remainsfound within archaeological sites? How do wedistinguish between natural ecological fluctua-tions and those caused by humans? How suscep-tible is a particular marine ecosystem to humaninterference? These are questions ecologists aremuch more qualified and capable of answeringthan archaeologists are. How do we identify evi-dence for resource depletion in marine species?Intertidal shellfish beds are often considered tobe highly susceptible to human overexploitation,but shellfish (and other) populations can also bedestroyed or depleted by disease, nonhuman pre-dation, sedimentation, heavy storms, changes inwater temperature, and other problems unrelatedto humans. For these and other reasons, we needto look for evidence of human impacts not just inindividual archaeological sites but in regionalrecords. To most effectively examine the impactsof humans on marine ecosystems, we shouldfocus on long and nearly continuous sequenceswithin relatively small areas, such as the 7,300-year-old sequence at Otter Point on San MiguelIsland (Figure 1.2).

Paying particular attention to problems oftemporal resolution and geographic scale, wemust also find ways to compare archaeologicaldata more effectively—often anchored by radio-carbon chronologies with resolution measured incenturies—to historical and ecological data thatare often much more fine grained. For instance,northern elephant seals (Mirounga angustirostris)




were abundant along the Baja and Alta Califor-nia coast before being driven nearly to extinctionduring the first half of the nineteenth century byhunters who rendered their blubber into a com-mercial oil. Since Mexico officially protected atiny relict population on Guadalupe Island in AD1911, however, elephant seal populations alongthe Pacific Coast have recolonized much of theirhistorical range and expanded to over 150,000animals (Ellis 2003:193). Such a dramatic recov-ery, similar to the story of the California sea otter(Enhydra lutris), is heartening for conservation-ists but raises fundamental questions about thearticulation of archaeological, historical, and eco-logical records. If California Indians temporarilyeradicated sea otters or elephant seals from theirhunting territories or even the entire ChannelIslands, could we recognize such rapid declineand recovery cycles in the archaeological record?These and other problems are yet to be resolved,but some of the primary methods archaeologistsand ecologists are using to identify and under-stand human impacts on marine ecosystems arebriefly summarized below.

Resource Depletion and Depression

For archaeologists, one of the most visible typesof evidence for localized human impacts on

marine fisheries may be found in cases ofresource depression, or other changes in thetypes of resources people used through time.As predicted by foraging theory, humans enter-ing a given environment will initially focus onharvesting a suite of optimal or “high-ranked”resources that provide relatively high nutritionalor other (furs, raw materials for tools, etc.)yields (Grayson 2001). Although high-rankedresources are often assumed to be large animals,this is not always the case in aquatic environ-ments, where relatively small shellfish or fishcan often be mass harvested in large quantities.Because human groups often contain a diversearray of individuals (of different ages, sex, craftspecialists, social class, etc.), and many coastalecosystems offer a wide array of foods, the rangeof resources considered “optimal” by coastalgroups may be diverse and related to populationsize. If intensive harvesting of high-rankedresources reduces their productivity (density,size, accessibility, etc.), people may choose tospend more travel time to access them, switch tolower-ranked alternatives closer to home, or adevelop a combination of strategies. Eventually,however, a depletion of local resources and theincreased travel time invested in making a livingmay lead to the movement of a village or otherresidential base.


FIGURE 1.2. A Holocene dune in the Otter Point area on California’s San Miguel Island,where at least 10 stratified shell midden components spanning the past 7,300 years havebeen identified; note figures atop dune for scale (photo by J. Erlandson).



As mentioned earlier, cases of localizedresource depression are relatively common inthe archaeological record, especially in coastalareas where people were often relativelysedentary. Changes in the diversity or relativeimportance of subsistence resources har-vested through time, especially within a sin-gle occupational component, may provide evi-dence for localized resource depression.Archaeologists must be careful, of course, toevaluate other possible causes of suchchanges, as numerous natural processes(storms, sedimentation, disease, other preda-tors, water temperature, etc.) can lead to areduction in the density of local marine popu-lations. Noncultural variables such as climatechange have recently been documented in twointerior regions and appear to have affectedhuman hunting and encounter rates (Byers etal. 2005; Wolverton 2005). Nonetheless, whencombined with other evidence for human pre-dation pressure, cases of people switching todifferent resources or resource depressionmay provide valuable evidence for humanimpacts on marine communities. We cannotautomatically assume, however, that evidencefor localized depletion is equivalent to widerdegradation of an ecosystem, as heavy localexploitation can be combined with residentialmobility in a sustainable economic strategy.

Size or Age Changes in Marine Populations

Historical data suggest that heavy fishing pres-sure on many fish and shellfish species oftenreduces the average size or age of local orregional populations. Such changes can have adisproportionate effect on the productivity of aspecies, since larger and older individualsnearly always are breeding adults and tend tolay more eggs or have more offspring thanyounger or smaller adults. In the past, sucheffects may sometimes have been alleviated bytechnological limitations such as the size orstability of boats, the strength of nets or fishingline, and so forth. The size and age structure ofmarine populations can also be affected by a

variety of noncultural factors alluded to earlier,including predation by other animals, stormevents, changes in water temperature, andmarine productivity. Even the life histories ofcertain species, including changes in growthand maturation rates, can be altered by inten-sive predation (Reitz and Wing 1999:314).

Despite these problems, temporal changesin the average size or age of individuals from aparticular fish or shellfish species are one of thesimplest, most common, and valuable measuresused by archaeologists to reconstruct shifts inhuman predation pressure and impacts inmarine or aquatic ecosystems (see Broughton2002; Butler 2001; Claassen 1998; Erlandson etal. 2004; Jerardino 1997; Koike 1986; Lightfootet al. 1993; Mannino and Thomas 2002;Swadling 1976). Sample size is a critical issue insuch analyses, so that they are best focused onmajor prey species that are well represented in aseries of strata or sites. Geographic and tempo-ral variability in the size and age of local popula-tions can also be a problem, so such analysesmay best be applied to long and relatively con-tinuous sequences within a single site or a rela-tively small area. However, Klein et al. (2004)recently used variation in average shellfish sizefrom a relatively broad area of the South AfricanCoast to effectively identify changes in predationintensity between Middle and Late Stone Agepeoples. One of the great advantages of averagesize or age studies for zooarchaeological assem-blages is that they can be readily compared topaleontological, historical, and recent ecologicaldata sets to construct relatively long and contin-uous records of change in marine ecosystems(see Steneck and Carlton 2001).

Reductions in Geographic Range

One of the reasons marine animals have histor-ically been more resistant to extinction causedby humans is that they often had geographicrefuges where humans were incapable of cap-turing them, either in deeper offshore waters,remote and inaccessible stretches of coastline,or on offshore islands. As humans expanded


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around the globe and developed increasinglyeffective maritime technologies, these refugesgradually shrank and were probably increas-ingly limited to deeper waters and more remoteislands that humans had not yet reached.Remote island populations of pinnipeds,seabirds, sea turtles, and other animals thatspent part of their life cycle on land were espe-cially vulnerable to human impact, as they oftenbred, laid eggs, roosted, or rested in terrestriallandscapes devoid of large predators. Whenmaritime peoples first arrived on such islands,or recolonized them after sustained absences,they often had a heavy impact on such verte-brate populations.

If we can accurately reconstruct the distri-bution of such animal populations prior to thearrival of humans, the study of faunal assem-blages from archaeological sites has greatpotential for understanding the impacts thatboth prehistoric and historic peoples had on thedistribution of seabird colonies, pinniped rook-eries, and other animal aggregations. A num-ber of studies have implicated human huntingas the cause of impacts on the prehistoric dis-tribution of pinniped rookeries and haul-outs inthe Pacific (e.g., Anderson 2001; Bryden et al.1999; Burton et al. 2002; Hildebrandt andJones 1992, 2002; Jones and Hildebrandt 1995;Lyman 1995), for instance, and archaeologicaland historical accounts have both contributedto an understanding of the reduction in the geo-graphic range of walrus in the North Atlantic(see Mowatt 1984).

We should be cautious about attributingchanges in the distributions of such animalssolely to human impacts, however, because avariety of other processes can affect both theirdensity and distributions. Along the PacificCoast of North America, the geographic range,feeding patterns, and behavior of marine mam-mals have been altered by the historical deci-mation of their own populations as well asthose of their predators and prey (see Burton etal. 2002; Estes 1998; Etnier 2004). Hilde-brandt and Jones (1992) proposed that earlyhunting by Native Americans eradicated

numerous mainland rookeries, for instance,but mainland rookeries were probably alwaysrare because of their vulnerability to grizzlybears and other predators (Erlandson et al.1998:12). Coastlines are also extremely dyna-mic and were even more so with rapidly risingpostglacial sea levels, so that coastal erosionmay also have destroyed many small islets orislands that once contained nesting colonies,rookeries, and haul-outs. Finally, it is not alwaysclear that the naive behavior of some modernanimal populations would have persisted undersustained human hunting, and some seabird,pinniped, or other colonies may have beenabandoned for more remote locations, withouta regional depletion of an animal population.

Trophic Cascades

One of the basic tenets of ecology is that thecomponents of an ecosystem are inextricablylinked—one component does not change with-out affecting others—although the linkages maynot always be immediate or easily recognized.Given this fact, we should expect heavy humanpredation on a particular marine species to havea corresponding effect on the competitors, prey,or predators that the depleted species stronglyinteracted with (Suchanek 1994). In some cases,including those pinnipeds or seabirds that feedin very deep waters or far offshore, a reductionin local population may have only minor effectson nearshore coastal ecosystems. In otherscases, however, a reduction in some “keystone”species can have dramatic effects that set off“trophic cascades” or create “alternative stablestates” within coastal ecosystems.

Trophic cascades caused by human overfish-ing have been documented in North Americankelp forest ecosystems from the Aleutians, Cal-ifornia, and the Gulf of Maine (Estes et al. 1998;Jackson et al. 2001; Simenstad et al. 1979;Steneck et al. 2002, 2004), where the removalof apex predators such as cod and sea otterscaused dramatic regime shifts in local andregional nearshore ecosystems. These casestudies demonstrate the diversity of responses


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to human impacts in similar ecosystems foundin various regions. In the North Pacific, themost profound and immediate impacts appearto have occurred in Aleutian kelp forest ecosys-tems, where species diversity is relatively lowand the removal of a single “keystone” predator(sea otters) can have dramatic effects, creatingtrophic cascades and alternative stable statecommunities. In the Aleutians, the removal ofsea otters by Aleut and Russian hunters alloweda rapid proliferation of sea urchins that over-grazed nearshore kelp forests and created“urchin barrens” that support a much less pro-ductive and diverse suite of marine resources.Several cycles of kelp deforestation have beendocumented in the Aleutians, the most recentbeing the result of heavy killer whale predationon sea otters (Estes et al. 1998; Steneck et al.2002).

In the more diverse food webs of the south-ern California Coast, in contrast, the eradica-tion of sea otters from much of their historicalrange during the early 1800s had dramaticeffects on nearshore ecosystems but nevercaused the wholesale collapse of kelp forests,probably because other predators such assheephead and lobsters helped keep urchinpopulations in check. On San Miguel Island,however, understanding the dynamics of suchtrophic interactions has allowed us to tenta-tively identify some ecological changes that maysignal localized impacts by Chumash Indiansthousands of years ago. One of these is found inthe proliferation of large red abalone middensbetween about 7,500 and 3,000 years ago, anarchaeological site type that modern ecologicaldata suggest could not exist unless sea otterspopulations were held in check, probably bynative hunting (Erlandson et al. 2005).

In cases like that of the sea otter, whichstrongly influence the structure of nearshorebiological communities, understanding theecological consequences of heavy marine fish-ing or hunting of keystone species in coastalecosystems can help develop a series of predic-tions for what related changes might be visiblein the archaeological record. In many cases,

such predictions can be developed from mod-ern ecological studies and historical fisheriesdata that can also provide strong support forarchaeological inferences about ecologicalchanges in marine ecosystems caused or con-tributed to by humans. In our experience, how-ever, the active participation of marine ecolo-gists is a crucial component of such modelingand analyses.

Fishing Down Foodwebs

A relatively new quantitative method for under-standing human impacts on fisheries wasintroduced by Pauly et al. (1998) in an influen-tial quantitative synthesis of marine fishingpractices in recent historical times. Usingtwentieth-century fisheries and ecological dataon the average trophic level of economicallyimportant species, Pauly et al. (1998) identifieda pattern of declining average trophic level inregional and global fisheries over time. Theyargued that this pattern reflected an intensiveearly focus of most commercial fisheries onrelatively large and long-lived carnivores (e.g.,cod, haddock, tuna, swordfish). When thesefisheries declined or collapsed, the emphasis ofcommercial fishing switched to higher propor-tions of smaller fish (herring etc.), inverte-brates (lobster, shrimp, shellfish, etc.), andother organisms that generally fill the lowertrophic levels of ecosystems. Historically, sus-tained overfishing of some key predatoryspecies (cod etc.) can lead to “ecological extinc-tion” or “ecological ghosts,” where a species isstill present in an ecosystem but its numbersare so depleted that it no longer fills its normalecological role. In cases like that of the seaotter, this can lead to the creation of trophiccascades and dramatic phase shifts in marineecosystems, such as those described above forthe Aleutian Islands (Estes et al. 1998; Simen-stad et al. 1978; Steneck et al. 2002). Anotherclassic example is the historical overexploita-tion of the Atlantic cod (Gadus morhua) andother large apex predators in the Gulf of Maineand the western North Atlantic (see Jackson




et al. 2001; Steneck et al. 2002, 2004). Here,the ecological extinction of large nearshore fishreleased predatory controls on herbivorous seaurchins, which then greatly reduced the pro-ductive three-dimensional kelp forest habitatsthat appear to have dominated a relatively sta-ble ecosystem for thousands of years. Afterheavy commercial fishing of sea urchins beganin the late 1980s, however, kelp forestsreturned to the ecosystem, but the apex preda-tor role is now filled by invertebrates (crabs). Inthis process of “accelerating trophic-level dys-function,” the average trophic level of marinefisheries has declined substantially (Stenecket al. 2004).

It is still not clear how much such historicalexamples may apply to prehistoric fishing prac-tices, but the use of quantitative trophic levelanalysis has the potential to help bridge the gapbetween archaeological, historical, and ecologi-cal data on human impacts to marine fisheries(see Morales and Rosello 2004; Reitz 2004:63).For ecologists and fisheries managers, it pro-vides a technique to explore changes in marinefisheries over much greater time depths andreexamine the shallow historical baselines onwhich fisheries management policy has longbeen based. As Reitz (2004:63) noted, the tech-nique provides archaeologists a new perspec-tive for understanding changes in archaeologi-cal fish faunas and an opportunity to usearchaeological data to help restore marineecosystems. So far, archaeological applicationsof trophic level analysis have been limited, butwork by Reitz (2004) and Steneck et al. (2004)has provided important case studies for coastalarchaeologists and marine ecologists to buildon. We should not expect, however, that the pat-terns of the twentieth century will necessarilyhold true through long periods of archaeologi-cal time. On California’s Channel Islands, forinstance, one of the secrets to the relative sta-bility of indigenous fisheries over 10,000 years(Erlandson et al. 2005; Rick et al., this volume)may be that the Chumash and their ancestorsappear to have focused first on the lowertrophic levels, relying heavily on shellfish and

smaller nearshore fish during the Early andMiddle Holocene.

SUMMARY AND CONCLUSIONS

Throughout human history, the oceans gener-ally appear to have been more resistant tohuman impact and degradation than terrestrialecosystems. This fact is probably due to a com-bination of factors, including the longer historyof hominid exploitation of terrestrial land-scapes, the susceptibility of terrestrial land-scapes to fire, the limited physiological andtechnological ability of humans (or their dogs,rats, pigs, etc.) to access deeper or more remoteaquatic habitats, and the greater resistance ofmost marine organisms to diseases carried byhumans and our domesticated companions.Our hominid ancestors may have used marineand aquatic resources to some extent for mil-lions of years, but archaeological and anthropo-logical data suggest that the intensity, diversity,and technological sophistication of aquaticresource use increased significantly after theappearance of anatomically modern humansroughly 150,000 years ago (Erlandson 2001;Erlandson and Fitzpatrick 2006).

Through the comparative approach of his-torical ecology, archaeologists have the opportu-nity to evaluate the evolution of human impactson marine ecosystems through time and space.In the process, we can contribute valuableinsights into one of the most important ecolog-ical problems currently facing humanity. In sodoing, we can strengthen the relevance ofarchaeology in the modern world, as well as thearguments for increased protection of archaeo-logical sites and increased research on thearchaeology of coastal societies around theworld. In the process, however, we should becautious in how we interpret archaeological evi-dence for human impacts in marine ecosys-tems. We should be equally cautious in our useof historical and ecological data on the demog-raphy of marine species and the structure ofpast ecosystems, for in many cases historicalor modern patterns have been affected by




centuries or millennia of anthropogenic influ-ence. Differences in both temporal and spatialscales should also be carefully considered, andfurther work needs to be done on the methodsand theory required to effectively integrate pale-ontological, archaeological, historical, and eco-logical data sets.

For archaeologists and ecologists, evidencefor human impacts on marine fisheries may befound in cases of resource depression, deple-tion, or shifting, changes in abundance andgeographic distribution, reductions in size orage profiles for specific populations, in trophiccascades, or in changes in the average trophiclevel of marine species harvested. Understand-ing the nature of trophic cascades or otherrecent impacts documented with historical orecological data can provide models that canhelp us understand the potential impacts ofhumans on marine ecosystems. On Califor-nia’s Channel Islands, for instance, marineecologists have provided new insights on oldarchaeological problems by helping us betterunderstand the dynamic historical ecologicallinkages between humans, sea otters, abalones,and sea urchins, and some previously unsus-pected impacts of the Island Chumash on kelpforest ecosystems (Erlandson et al. 2004,2005; Rick and Erlandson 2003). At the sametime, we have learned that the biological diver-sity of Channel Island kelp forests makes themconsiderably more resistant to ecological col-lapse than the less-diverse kelp forest ecosys-tems of the Aleutian Islands and Gulf of Maine(Jackson et al. 2001; Steneck et al. 2002), help-ing explain why the Chumash and their ances-tors may have had relatively limited impactsduring a history of systematic fishing andhunting that spans more than 10,000 years(see Erlandson et al. 2005; Rick et al. this vol-ume). Anderson (2001) and Kirch (1999) havemade similar points about variation in the pro-ductivity, diversity, and resilience of differentPacific Island ecosystems. Before we indictsome human societies for excessive environ-mental degradation and celebrate others fortheir sustainability, we would do well to thor-

oughly understand the ecological and historicalunderpinnings of their successes and failures(see Rainbird 2002).

Despite tremendous variation in coastal cul-tures and ecosystems around the world—andwhat we suspect are a variety of adaptive trajec-tories that vary widely in their success—itseems reasonably clear that there is a generalgeographic expansion of human impacts tomarine ecosystems over time. These began insupratidal and intertidal zones, expanded tosubtidal and nearshore waters, then to pelagiczones not far from land, to island arcs more andmore distant from the continents, to the vastand relatively empty expanses of the Atlantic,Pacific, and Indian oceans, and other oceans.Although these large oceanic expanses weretraversed by Austronesians/Polynesians, Vikings,and others, their resources were largelyuntouched by humans until the advent of whal-ing and other industrial fishing technologies ofthe eighteenth, nineteenth, and twentieth cen-turies. Archaeology is obviously positioned toilluminate the expansion of marine, estuarine,and freshwater fisheries during prehistorictimes, but it may also shed considerable lighton some poorly documented fisheries of thehistoric era, such as the Chinese abalone fish-ers of Alta and Baja California in the mid- tolate 1800s (see Braje et al. 2007). As a variety ofstudies have shown (see Jackson et al. 2001;Steneck et al. 2002, 2004; and the case studiesthat follow), archaeological data can play a keyrole in defining the acceleration of humanimpacts to marine ecosystems through time,the development of more realistic notions ofthe abundance of past populations prior toindustrialized fishing, and the reconstructionof more effective historical baselines for thefuture restoration and management ofaquatic fisheries and ecosystems. With thisvolume, we hope to highlight that potential,encourage further interdisciplinary workbetween coastal archaeologists and marineecologists, and inspire ecologists, archaeolo-gists, and others to pursue new directions intheir research.


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