oyster sources and their prehistoric use on the georgia coast

Oyster Sources and Their Prehistoric Use on the Georgia Coast

Morgan R. Crook, Jr.“

(Received 2 Januar>~ 1991, revised manuscript accepted 30 January 1992)

American oysters (O~wostrra virginica Gmelin) on the Atlantic coast of south-eastern North America occupy distinctive habitats which arc associated with communities that share common variation in the shape of their shells. Oysters from archaeological contexts are analysed and their variation compared to that represented in each modern community type. Source types for archaeological oysters are successfully identified (0.05 level of significance) for I2 of the I4 archaeological contexts by applying a simple analysis of variance proccdurc. The results indicate that much of the prehistoric oyster gathering may have been carried out by women and children. and that the recurrent harvesting of oysters from one of the community types had positive effects on subsequent yields.

Kr~wortl.c: OYSTERS, SPATIAL VARIATION. SIMPLE ANALYSIS OF VARIANCE. DIVISION OF LABOUR.

Introduction The American Oyster (Crassostrea virginica Gmelin) is abundant today within estuarinc waters of south-eastern North America. These oysters also are the principal components of shell middens found at archaeological sites along the coast, attesting to their continued use as an aboriginal subsistence resource over a period of at least 4500 years. Much archaeological attention has been given to shell middens and their associations within this region and in many other coastal areas world-wide, and an excellent summary was recently presented by Waselkov (1987).

Archaeological research dealing with shell middens traditionally has been concerned with the dietary importance of molluscs versus maritime vertebrate species and with determining the season of their exploitation. Accumulating evidence from the south- eastern coast indicates that oysters were an important complement to a broad-spectrum and relatively stable estuarine and maritime oak-forest subsistence regime. Oysters were a locally abundant, dependable, easily exploited resource that nevertheless provided low caloric yields compared to other principal food resources (see Larson, 1980; Milanich & Fairbanks, 1980; Trinkley, 1980; Crook, 1986; Reitz, 1988; cf. Quitmyer, 1985). Only competing tentative conclusions now are available about seasonal variation in the collection of oysters and most other subsistants along the south-eastern coast, primarily because seasonal variability among the food resources themselves is quite limited. It has been variously argued that oysters usually were gathered from the late autumn to early spring months (Crook, 1986), or primarily during the winter and spring months (Claassen, 1986). or during all seasons of the year (Russo, 1991).

483

4x4 M. R. CROOK

Research reported here departs from these traditional questions of subsistence and seasonality to focus on evidence for spatial variation of natural habitats used in gathering oysters. Specifically, this inquiry assesses variation in certain characteristics of contemporary oysters from distinctive natural habitats and attempts to match these varying characteristics to those observed in oysters from archaeological contexts. In doing this, the goal is to determine at a reasonable level of confidence, the specific kind of oyster habitat that was the source for oysters represented in archaeological deposits and to assess, at least in an initial way, the significance of different source habitats.

A similar line of inquiry also has been pursued in archaeological research along the middle Atlantic coast. Here, Kent (1988) suggests that it is usually possible to discriminate oyster source habitats based upon associated differences among mean shell height-to- length ratios and accompanying evidence of shell clustering. However, he cautions that these characteristics do not form discrete categories since there is “considerable overlap between oysters from different habitats” (Kent, 1988: 30).

Significant differences exist between the ecological characteristics of coastal Georgia, the research area considered here and the coastal Maryland area considered by Kent. Differences in temperature, tidal ranges, bottom conditions and estuarine structure com- bine to effect the growth and form of oyster communities somewhat differently in each region (Galtsoff, 1964; Odum, Copeland & McMahan, 1974). One reflection of this ecological difference is the greatly increased overlap of mean height-to-length ratios of oyster shells from various habitats on the Georgia coast. The specific analysis techniques, habitat types and oyster forms identified in coastal Maryland are not directly applicable to the Georgia coastal ecosystem and its archaeological record.

The research locale for the analysis reported here is Sapelo Island--a barrier island along the Georgia coast-and its adjacent estuarine system (Figure I). The specific research results are considered applicable to similar ecosystems along the south-eastern Atlantic coast and the methods employed may prove to be useful in approaching similar research questions in other coastal areas as well.

Contemporary Oysters and Their Habitats Oysters thrive within the intertidal zone along estuarine rivers and the maze of tidal creeks that dissect the expansive Spurtina marsh system separating barrier islands from the mainland along the Georgia coast. Subtidal oysters also are present but are uncommon. A I97477 survey of the Georgia coast (Harris, 1980) recorded 117 ha of oyster beds; 86% were in the intertidal zone. Compared with a 1889 oyster survey (Drake, 189 I), this areal extent indicates an 87% decline in the total oyster population during the past century. It is likely that this dramatic decline is due largely to poor management practices, particularly the failure to reseed oyster beds after harvests.

Although the overall quantity of oysters has diminished, their distribution appears to have remained relatively stable. Oysters are limited to those areas along the banks of tidal streams that provide relatively stable substrates that allow larvae an opportunity to settle and grow. Once established, even if in less favourable softer substrate, oysters themselves provide a setting surface for future generations (Galtsoff, 1964; Bahr, 1974).

As the distribution of suitable substrate varies along the tidal streams, so too does the distribution of oyster communities. The four basic types of intertidal oyster communities, each associated with distinctive habitat characteristics, are defined here as Singles, Clusters, Banks and Reefs.

Communities of Single oysters, together with small clumps of from two to six oysters, grow within the lower portion of the intertidal zone along small tidal creeks. They are dispersed along these creeks within soft mud that covers a firm substrate. Although survey

OYSTER SOURCES ON THE GEORGIA COAST 485

SAPELO SOUND

ATLANTIC

OCEAN

Figure I. Sap& Island and adjacent estuary. Locations of’ sampled oyster communities and tested archaeological sites are shown. I. Singles Communit) along Barn Creek; 2. Cluster Community along the Duplin River: 3. Bank Community along the Duplin River; 4. Bank Community along the Little Mud River; 5. Reef Community along the Mud River. A. Sapelo Shell Ring site; B. Kenan Field site; C. Bourbon Field site.

assessments are not available, communities of this type appear to be rather rare and the total number of oysters within any single community is probably relatively few.

Cluster communities, typically composed of small clumps of from 10 to 30 attached oysters, are found scattered along larger tidal streams either on relative firm bottoms adjacent to stream channels or on softer muddy bottoms within tidal flats. These oysters are vertically distributed throughout the intertidal range. This type of community is common and the total number of associated oysters is probably considerable. However, it seems that oyster surveys have failed to document their full distribution.

Bank communities, composed ofcontiguous individual clusters of 30 or more attached oysters, also are located along the banks of larger tidal streams and occupy much of the

486 M. K. CROOK

intertidal range. These linear aggregations are typically from 2-4 metrcs wide and may extend 50 m or more in length. They are formed either on naturally firm substrate or on an oyster substrate created by successive generations of former Cluster communities that have expanded horizontally. In total area covered and in total number of oysters, this is the dominant community type along the Georgia coast and is also the principal source of commercial oysters today.

Reef communities, composed of very dense and closely spaced clusters of 30 or more oysters each, also are located along larger tidal streams. The living Reef community is attached to the top and sides of dead oyster substrate that may be as much as 2 m thick. Reefs are located in optimal environments where water currents transport sufficient nutrients to maintain a dense oyster population. The height of reef accretion is limited by minimal water level of high tides. Once this limit is approached, growth of the reef can only continue laterally towards the stream channel. As a result, Reef communities are much wider than Bank communities and contain more closely spaced oysters. Oyster Reefs may be 10 m or more wide with usual lengths of as much as 20 m. Although not critically distinguished in existing oyster surveys, they are far less common than Bank communities and the density of oysters within Reef communities is much greater due to increased competition for available space.

Each of these communities provides a different environment for oyster growth. Whereas oysters are immobile creatures which are fixed in their environment, there is a general relationship between shell shape and growth habitat. Single oysters growing on firm bottoms tend to have rounded shells, while Cluster, Bank and Reef oysters tend to be long and slender (see GaItsotT, 1964: 18). Spacing within their habitat appears to be a critical factor. Individual oysters are compelled to grow primarily upward rather than outward as competition for available space increases. The result is that a common range in shape variation may be expected among oysters growing in similar habitats, and this variation should be different among the different growth environments.

Samples of living oysters were collected from each of the four types of oyster communities to determine if variation in shell shape was associated with each defined type. The samples were collected by hand at low tide during December 1980 and February I98 I. While not strictly random samples, individual oysters were selected arbitrarily from each location and are considered to be generally representative of their respective communities. The only recognized exception to this statement is that very small oysters (less than 4 cm in height) were avoided in four of the samples. In an additional sample of commercially collected oysters, this bias may have been somewhat greater.

Four of the oyster samples were collected from intertidal areas adjacent to Sapelo Island and the fifth commercial sample was collected from a nearby location to the north. Samples were collected from a Singles community along Barn Creek, from a Cluster community along the Duplin River at the Kenan Field archaeological site, from a Bank community along the Duplin Riverjust above Barn Creek, from another Bank community along the Little Mud River near Harris Neck (the commercial sample) and from a Reef community along the Mud Riverjust north of the Sapelo Shell Ring archaeological site (see Figure I).

A standard series of measurements were taken on oysters in each sample. Soon after gathering, oysters were opened and drained meat weights were recorded to the nearest whole gram. The meats of each oyster within four samples and 50 of the 133 commercial oysters were weighed. The maximum height and length of the left (cupped) valve of oysters within all samples then were measured to the nearest millimetre (Figure 2).

Descriptive summaries of the recorded measurements, along with shell height-to-length ratios (H/L) and overall size indices 6 L. are shown in Table I Overall size index provided the strongest correlation with meat weight; least-squares regression lines for


+ Length ---+

Barn Crk Duplin Singles (‘lusters h’ = 60 N= 50

Duplin Bank

N=50

L. Mud River Bank

,v= 133<50>

Mud River Reef

N= 100

height (mm) mean) S.D. Length (mm) meani S.D. lleight length mean & S.D. Si/e index n1can~S.D Meat(g) man + S.D

92.95 2 12.43

54.38 2 5.23

I.73 20.30

70.83 + 5.S6

I l-97 & 3.82

75.08 f 15.77 45.54

t_9.14 I.67

& 0.29 58.13

& I I.06 3.38

* I.05

75.42 & IO.17 44.38

+ 9.60 - I.74 * 0.40

57.51 * I I.91

3.26 * I .6X

80.29 * 28.56 44.1 I

* I I.08 I.80

io.41 59.16& 16.93

<60.13* 15.562

< 5.56 r 3.66 >

106.53 + 19.75

34.22 i 5.25

:.I4 &(I,56 60. I6 & 8.98

4 60 + 2.00

488 M. R. CROOK

. . ., . . . . . . . .

100 -

0 5

Meat weight (g)

IO

Figure 3. Linear regression of meat weight and shell size per type of oyster community.

oysters from each community type are shown in Figure 3. The statistics indicate that the largest oysters with the most meat are members of the Singles community and that oysters from the Reef community are long and slender, having much greater height-to-length ratios than oysters from other communities. Although it was suspected that shell length would gradually become reduced relative to shell height among oysters from increasingly dense communities, this general pattern is not immediately apparent. The standard deviations of mean height-to-length ratios, and other measurements as well, indicate that considerable variation exists within each of the sampled communities and also that expressed standard deviations overlap significantly between the communities.

Another method was used to determine whether the variation in height-to-length ratios represented among oysters was significantly different or equivalent between community types. Simple analysis of variance employing the F-test (Blalock, 1979: 336346) was used to test for significant differences in variation of shell shape between the sampled oyster communities. Test assumptions are normality, independent random samples and equal population standard deviations; none of these necessary assumptions appears to be seriously violated. The null hypothesis for testing is that variation in height-to-length ratios between two samples is equal, representing equivalent populations. The alternative hypothesis is that variation in height-to-length ratios between two samples is not equal, and thus represents different populations. In order to determine whether or not to reject the null hypothesis, and to accept the alternative hypothesis, one-tailed tests at the 0.05 significance level were chosen. The F value derived from comparison of two sample variances then was compared to the expected F value as shown in a standard statistical table for the distribution of F for varying sample sizes (N) (Freund, 1962: Table Via; Blalock, 1979: Table J). The null hypothesis was accepted when the calculated F value was less than or equal to the expected F value. The null hypothesis was rejected and the

OYSTER SOURCES ON THE GEORGIA COAST

Table 2. Re.wdis of unalysis qf vuriance umong modern oyster communities

489

Sample community type (A) (B) (Cl CD) (E)

(A) Barn Creek Single (N=60) (B) Duplin River Cluster (N= 50) (C) Duplin River Bank (N=50) (D) L. Mud River Bank (N= 133) (E) Mud River Reef (N= 100)

(1Y5) (158)

(1i5) (A)

(48) (Pi,)

(1 r;90) (1x99) = (1.06)

(3.x48) (3.:5) iG5)

(I .“90) (3.:8)

(1x99) (3.i5) =

(1.06) $5)

(li(84)

(1.84)

Significance at the 0.05 level. =Indicates acceptance of the null hypothesis of equal populations x Indicates rejection of the null hypothesis. Numbers in parentheses are F values.

alternative hypothesis accepted when the calculated F value exceeded the value presented in the table. With the choice of critical limits set at 0.05, it is accepted that the null hypothesis will be rejected when actually true less than 5% of the time.

The analysis of variance test results are presented in Table 2. The null hypothesis of equivalent ratio variation was accepted between oysters from the Single and Cluster communities, indicating common variation among height-to-length ratios for these two types. The null hypothesis also was accepted between oysters in the two samples from different Bank communities, indicating that distinctive variation in shell shape is shared among the same community type in different estuarine locations. The alternative hypothesis was accepted in all other comparisons, indicating the samples were derived from distinctive populations.

The analysis of variance results indicate that variation in shell shape is discretely associated, at a 0.05 significance level, with three of the four community types. Oysters from Reef and Bank communities can be distinguished from one another and from oysters associated with either Single or Cluster communities. Those from Single and Cluster communities share common variation among their shell height-to-length ratios and cannot be discriminated from one another based upon this measurement. This is probably because oysters within these two communities are the least effected by competition for restricted space during their growth cycles.

The patterned variation within the oyster community types has potential archaeological significance. The height-to-length ratios of shells from archaeological deposits can be measured and the sample variations compared with those expressed in the modern samples. Assuming that similar environmental constraints were operating within both modern and prehistoric oyster populations, the results should indicate the original type of source community for the archaeological specimens.

Oysters from Archaeological Contexts Prehistoric archaeological sites on Sapelo Island, ranging in time from about 2500 BC until AD 1540, are well represented and are almost always associated with oyster refuse (Juengst, 1980). Three of the better-known sites have been tested extensively and provide data which allow comparisons with the modern oyster samples (Figure 1). The Sapelo Shell

490 M. R. CROOK

Shell height (mm) Shell length (mm) llcight length SIFT lndcx , H x I_ n1ean k S.D. mean f S.D. mean * S.D. mean* S.D.

Shell Ring (h’= 100) 12.52 _+ 22.5 I Kenan F/205 (N= 100) X8.08*26.31 Kenan FOAZ (N ~ 88) 81.67_+21.32 Kenan FOA3 (N= 100) X9. I 1 + 24,86 Kenan SMI 12 (IV= 100) 62.921 14.19 Kenan SMl03 (N= 100) 80,16& 17.54 KenanSM113(N=XO) 58.24k IO.08 Kcnan SM245 (N= 100) 78.83 + 24.82 Kenan SM108 (N= 100) 58.X6& 12.13 Bourbon F/Z (N= 75) 74.712 17.10 Bourbon SM2 (N= 100) 91.23F 19.19 Bourbon SM128 (N= 105) 76.32 + 20.94 Bourbon SM30 ( IV= 100) 84.74 F 18.82 Bourbon SM 143 (N = IO()) 78,66_+21.95

31.26 i 9.76 41.73 +9.3s 42.95i I I.13 43.59 F IO.08 42-23 f 7.5 1 48.19*x.52 40.45 + 7.00 40.97k9.51 40.321tr8.13 47.16F IO.65 43.07 * 9.43 45.19& IO.38 34.94k8.65 45.27i9.14

2.00 & 0.56 2,12+0,48 I .94 f 0.42 2,10_+0,60 I.51 io.31 1.70+0.45 I .46 + 0.24 1.96kO.54 1,49+0.30 I .63 & 0.43 2.19*0.55 I .72 i 0.46

2.52kO.67 1.77io.54

51.16+ 12.81 60.191 14.43 58.895 13.91 61.76& 13.63 51.31 k9.04 61.72+9.67 48.40 * 7.42 56.32 * 13.37 48.45 _+ X.80 59.37*11.00 62,16& IO.35 58.37 i 12.68 53,94& IO.38 59,12+ I I.34

Ring is a large circular shell-midden embankment that measures about 100 m across with a top surface that rises from 2.00 m to 3.75 m above the surrounding land surface. The ring is formed of oyster shell and other subsistence refuse deposited as a consequence of occupation on the ring during the Sapelo phase (c. 2500&1000 BC) of the Late Archaic period (Waring & Larson, 1968; Simpkins, 1975). Kenan Field is a multicomponent site covering 60 ha and containing 591 circular shell middens. The upper surfaces of all shell middens have been disturbed by modern ploughing, but the lower portions of the middens are predominantly undisturbed. Tested areas of the site indicate intensive occupation during the Savannah phase (L.. AD 1000 -1500) of the Mississippi period and more sporadic settlement during earlier and later periods (Crook, 1978). Bourbon Field is a smaller multicomponent site covering 14 ha and containing 119 circular shell middens. As at Kenan Field upper portions of the shell middens have been disturbed by ploughing, while deeper lower portions tend to be intact. Intensive occupation occurred at this site during the Wilmington phase (c. AD 700-1000) of the Woodland period, during the Savannah phase and during the Irene-San Marcos phase (c. AD 1500&1680) of the Proto-historic period. Less intensive occupation took place earlier during the Deptford phase (c,. 500 BC-AD 700) of the Woodland period and during the Sapelo phase (Crook, 1984).

Samples of oyster shell, consisting of measurable left valves, were chosen from 14 excavated contexts within the three sites. The height and length of each left valve was measured to the nearest millimetre (Figure 2). Statistical summaries of the shell measurements are presented in Table 3.

Ten of the oyster samples were collected from test pits excavated in the intact matrix of shell middens. These samples were recovered arbitrarily from throughout the excavation level and arc considered to be representative only of those oysters associated with the excavated area of the midden. Whether or not the samples are representative of the entire shell midden is unknown. The cultural processes involved in the accumulation of refuse to form shell middens are expectedly complex. ranging from single-event domestic activities to multiple-activity communal events. The continued use of some shell middens over long periods of time, or through consecutive occupations, further compounds thei depositional complexity. Important research remains to be done to document the anatomy of shell middens.


The remaining four oyster samples werecollected from undisturbed subsurface features. Each sample was recovered arbitrarily from throughout the fill and is considered to be representative of all oysters within the feature. In each case, the features appear to be associated with discrete activities or single events.

Descriptions of sampled contexts and their cultural associations follow:

I. Sapelo Shell Ring (Sapelo phase). Sample collected from a 30 cm thick shell stratum within a 2 x 2 m test pit excavated along the northern margin of the ring.

2. Kenan Field Feature No. 205 (Sapelo phase). Sample collected from this shell-filled oval to rectangular pit measuring 125 cm long, 60 cm wide and 55 cm deep. The feature is interpreted as the remains of an abandoned earth oven.

3. Kenan Field Feature FOA No. 2 (Savannah phase). Sample collected from this shell-filled oval to rectangular pit measuring 145 cm long, 125 cm wide and 54 cm deep. The feature is interpreted as the remains of an abandoned earth oven.

4. Kenan Field Feature FOA No. 3 (Savannah phase). Sample collected from this shell-filled round pit measuring 80cm in diameter and 67cm in depth. The feature is interpreted as the remains of an abandoned earth oven.

5. Kenan Field Shell Midden No. 112 (Savannah phase). Sample collected from the lower half of the shell matrix within a 1.5 x 2 m test pit; midden measures 3 m in diameter.

6. Kenan Field Shell Midden No. 103 (Savannah/Irene phases). Sample collected from the lower half of the shell matrix within a 1.5 x 2 m test pit; midden measures 7 m in diameter.

7. Kenan Field Shell Midden No. 113 (Savannah/Irene phases). Sample collected from the lower half of the shell matrix within a I.5 x 2 m test pit; midden measures 9 m in diameter.

8. Kenan Field Shell Midden No. 245 (Savannah:Irene phases). Sample collected from the lower half of the shell matrix within a I.5 x 2 m test pit; midden measures 15 m in diameter.

9. Kenan Field Shell Midden No. 108 (Savannah/Irene-San Marcos phases). Sample collected from the lower half of the shell matrix within a 1.5 m x 2 m test pit; midden measures 13 m in diameter.

10. Bourbon Field Feature Z (Wilmington phase). Sample collected from this shell- filled round pit measuring 70cm in diameter and 40cm in depth. The feature is interpreted as a refuse-filled pit.

1 I. Bourbon Field Shell Midden No. 2 (Deptford phase). Sample collected from the lower half of the shell matrix within a 2 x 2 m test pit; middcn measures 20 m in diameter.

12. Bourbon Field Shell Midden No. 128 (Savannah/Wilmington phases). Sample collected from the lower half of the shell matrix within a 2 x 2 m test pit; midden measures 23 m in diameter.

13. Bourbon Field Shell Midden No. 30 (Savannah phase). Sample collected from the lower half of the shell matrix within a 2 x 2 m test pit; midden measures 17 m in diameter.

14. Bourbon Field Shell Midden No. 143 (Savannah/Irene-San Marcos phases). Sample collected from lower half of the shell matrix within a 2 x 2 m test pit; midden measures 18 m in diameter.

Comparison of Archaeological Samples and Oyster Community Types

The analysis of variance test results (0.05 level of significance) comparing variation of shell height-to-length ratios for each archaeological sample with each modern oyster community sample are shown in Table 4. The null hypothesis for testing was that variation between a particular archaeological and modern sample is equal, indicating a match

492 M. R. CROOK

Archaeological context

Barn Creek Singles N=60

Duplin Clusters

N=50

Duplin Bank

N=50

L. Mud River Bank

N= 133

Mud River Reef

N= 100

Shell Ring (N= 100) Kenan F/205 (N = 100) Kenan FOA2 (N= 88) Kenan FOA3 (N= 100) Kenan SMI 12 (N= 100) Kenan SM103 (N= 100) KenanSMI13(N=80) Kenan SM245 (N = 100) Kenan SM108 (N= 100) Bourbon F/Z (N= 75) Bourbon SM2 (N= 100) Bourbon SM128 (N= 105) Bourbon SM30 (N = 100) Bourbon SM143 (N= 100)

x(3.61) x(2.53) x( I .99) x(3.97)

=(1.07) x(2.27) x(1.60) x(3.31) =(1.03) x(2.09) x(3.41) x(2.37) x(5.06) x(3.22)

x(3.78) x(2.65) x(2.09) x(4.16) =(1,12) x(2.37) ~(1.52) x(3.47) =(1.08) x(2.19) x(3.57) x(2.49) x(5.30) x(3.37)

x(2.02) =(1.42) =(1,12) x(2.22) x(1.67) ==(1,27) x(2.85) x(1.85) x( 1.73) E(l.17) x(1.91) =(1,33) x(2.84) x( 1~80)

x(1.90) =(1.33) =(1.05) x(2.09) x(1.77) z(l.20) x(3.03) x(1.74) x(1.84)

=(l,lO) x(1230) =(1.25) x(2.67) x( 1.69)

=(1.04) =(1,38) x(1.75) =(1.14) x(3.25) x(1.53) x(5.56) z(1.05) x(3.38) x( I .67) =(1,02) x( I .47) x(1.45) =(1.08)

Significance at the 0.05 level. = Indicates acceptance of the null hypothesis of equal populations

x Indicates rejection of the null hypothesis. Numbers in parentheses are F values.

between oysters forming the archaeological deposit and their type of source community. The alternative hypothesis was that variation between a particular archaeological and modern sample is not equal, thus indicating mismatches between the archaeological oysters and the type of oyster community.

The test results indicate that each of the modern oyster community types that can be distinguished from their variation in height-to-length shell ratios are represented in the sampled archaeological deposits. Discrete matches occur between source community type and archaeological samples in 12 of the 14 contexts. Five of these archaeological deposits represent Reef community oysters, four represent Bank community oysters and three represent either Single or Cluster community oysters. In one case (Kenan Field Feature No. 205) two community types were matched, indicating statistical error or perhaps that both were sources. In a single case (Bourbon Field Shell Midden No. 30) there were only mismatches, probably indicating a considerable mixture of source communities (Bank and Reef?) within the deposit.

Discussion It is concluded that the type of community that was the source for oysters within prehistoric archaeological contexts usually can be identified at a reasonable level of statistical confidence. Habitat conditions effecting the shapes of oyster shells today on the Georgia coast evidently arc very similar to those in the past, allowing community-distinctive variation in height-to-length ratios to be effectively compared over time.

While it is possible to determine the community type of oyster sources, the small number of contextual samples from each archaeological site and from each culture period limit other inferences. However, certain general implications may be considered at this point to illustrate the interpretive potential of oyster-source data.

OYSTER SOURCES ON THE GEORGIA COAST 49.1

Figure 4. Collection of oysters from a Reef Community: water level approximately at mid-tidal range.

The Principal of Least Effort (Garner, 1967) may apply to prehistoric oyster gathering, assuming all other factors are equal. The material results of minimizing energy expendi- ture in the collection and transport of oysters might be represented in archaeological deposits on Sapelo Island. A large Reef community of oysters is located very near the Sapelo Shell Ring and this is just the community type represented in the sample from the site. A Cluster community is located adjacent to the Kenan Field site and Bank communities are nearby: both are well represented in the archaeological samples here. Reef and Bank communities are located short distances from the Bourbon Field site and both are represented in the archaeological samples.

Of course, “all other factors” are seldom equal and it is difficult to be very far from any particular type of oyster community on the Georgia coast. Factors other than simple distance could have influenced selection of one community type or another for exploitation. One important other factor may have involved the kind of access provided to the oyster source. With few exceptions, oysters within Bank communities along stream banks can be gathered only at low tide and access to them requires a boat; expanses of marsh between such communities and the land will not support human weight. In contrary fashion, many Reef communities are located along the edge of high and relatively firm marsh near the land. Most of the live oysters here occupy the upper surface of the reef and may be gathered by crossing the marsh on foot when the receding high tide exposes the reef (Figure 4). Single communities located along small tidal creeks near land also can be approached on foot at low tide. Only those Cluster communities located adjacent to land can be successfully approached on foot, while the more numerous ones along marsh-bound streams require access by boat at low tide.

Societal division of labour, connected with factors of access, also probably effected oyster-gathering activities. Ethnographic accounts indicate that shellfish collection tends

494 M. R. CROOK

to be a rather casual subsistence cndeavour most often undertaken by women and children as part of their general food-gathering activities (see Waselkov, 1987: 97-99). Those oyster communities accessible from land would have been easily exploited by this sex and age group as part of their gathering routine. Archaeological deposits composed of oysters from Reef and Single/Cluster communities may be the result of this division of labour. Men. on the other hand, tend to engage in subsistence activities such as hunting and fishing that regularly take them some distance from their homes. On the coast this would have required travel by boat which inevitably would have led them past a great many oysters in Bank communities. These oysters could have been collected, either as a planned activity or incidentally, and transported back to the settlement. Oysters in archaeological deposits from Bank communities may be the result of this kind of male collection activity.

It is interesting that one third of the oyster contexts identified as to source were from Bank communities and that two thirds were from Reefand Single/Cluster communities. If oysters had been collected in proportion to their natural abundance, one wduld expect Bank communities to be the dominant source represented in the archaeological samples. The high incidence of oysters from the other communities probably means that prehistoric oyster collection on the Georgia coast was dominated by women and children as it tends to be among ethnographically observed simple shellfish-gathering societies elsewhere in the world.

Another factor to be considered in assessir,g variation in exploited oyster sources is meat yield. Unfortunately, this issue cannot be adequately addressed based on the results of this study. The shell measurements and statistical tests employed here were unable to distinguish between oysters from Single communities, having the largest meats per unit size. and those from Cluster communities which have much smaller meats. Using similar methods, a marine ecologist (Dame, 1972) also was unable to distinguish intertidal from subtidal oysters in samples from the South Carolina coast based upon shell height/length relationships although the meat weight of subtidal oysters was about 40% greater than intertidal oysters of comparable size and proportions. This is approximately the same difference in meat weight associated with comparable oysters from Single and Cluster communities. Other methods need to be developed to segregate these two community types. The meat weights of oysters of comparable sizes from Reef and Bank communities are roughly equal, neither offering a yield advantage that would encourage preferential exploitation.

A final matter to be considered briefly here is the impact of prehistoric exploitation upon the oyster communities. The descriptive statistics for samples from modern and prehistoric Bank communities are very nearly the same (refer to Tables 1, 3). This clustering ofmeans and standard deviations suggests that aboriginal exploitation did not significantly alter the populations. A different pattern emerges, however, when the statistics representing oysters from modern and prehistoric Reef communities are examined closely. Oysters in the prehistoric samples tend be smaller in height and their height-to- length ratios are consistently less. That is, prehistoric Reef oysters are smaller but have comparably greater lengths than their modern counterparts. These differences indicate that aboriginal exploitation dynamically changed the character of oysters in Reef communities. Intensive scheduled collection of oysters from the same Reef community could have caused this change. Intensive collection, even on an annual basis, would result in the gathering of oysters ofedible size from the reef and a reduction in oyster population density. Competition for available space and nutrients would be reduced for the remaining oysters. allowing them room for more lateral growth than would be possible in an unexploited reef. As nutrients and growth space per oyster increased. these remaining oysters also would have grown more rapidly. The net result was increased population vigour and smaller but more abundant oysters for subsequent harvests. This kind of

OYSTER SOURCES ON THE GEORGIA C’OAST 495

cultural modification and feedback loop in the natural oyster community appears analogous to the process of cultivation of wild plants.

It is clear that identification of source community types for oysters has the potential to contribute new information about the archaeological past. This case study has examined only a few archeological contexts and still fewer anthropological issues. Conspicuously absent here is a detailed examination of artefacts and ecofacts associated with the contexts. This kind of comprehensive analysis will be required before the significance of the spatial dimension of oyster gathering can be more completely understood.

Acknowledgements Appreciation is expressed to C. V. Waters and the able staff of the Georgia Department of Natural Resources on Sapelo Island for their continuing support of archaeological research on the island. Thanks also are extended to Sam Hillary, Frank Bailey and Jeffery Mitchem for their assistance in collecting the modern oyster samples, as well as to Michael Russo and Cheryl Claassen for their thoughtful reviews of the manuscript. The statistical analysis reported in this study was generated using The St~~ti.sti~.iun software program (Quant Systems, 1983) on an IBM-compatible XT computer. Copies of the raw data, written in BASIC, are available from the author. Requests should be accompanied by formated DS!DD 3.5” disk.

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oyster sources and their prehistoric use on the georgia coast

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