by Katie Sperry, graduate student at Northeastern University and the Plum Island LTER site
A recent paper from researchers at the University of Georgia, in collaboration with the Muscogee (Creek) Nation, uses oxygen isotope analysis of mollusk shells found at archaeological sites to show how ancestral Muskogean villages collectively, and sustainably, managed shellfish harvest.
Reconstructing the past
Within the Georgia Coastal Ecosystems LTER, in the ancestral homelands of the Muscogee (Creek) Nation, rings of mollusk shells have been unearthed during archaeological digs. Reaching almost 100 meters in diameter, these massive rings are the fingerprints of historical Muskogean villages. “These are some of the earliest village sites in North America, dating to the late archaic period, about 4,400 to 3,800 years ago,” says Dr. Carey Garland, the lead author on a recent paper in the Journal of Anthropological Archaeology which reconstructs the mollusk harvesting practices of ancestral Muskogean peoples by chemically analyzing the shells within these rings.
What’s in a shell?
As an oyster grows, it pulls molecules from the water column and uses them to build its shell. Consequently, an oyster’s shell is a physical record of its life and environment. This growth happens incrementally, so, as with an ice or sediment core, one can look at the layers of an oyster shell to reconstruct past conditions. One can even reconstruct human-nature relationships, such as oyster harvesting practices, from thousands of years ago.
Understanding historical harvesting practices is of particular significance when it comes to ancestral Muskogean peoples, as previous research has shown that they harvested mollusks sustainably for thousands of years. Unearthing details about how exactly mollusks were harvested without over-exploiting reefs for so long has contemporary significance given modern patterns of overharvest and resource exploitation.
To reconstruct these ancient harvesting practices, the researchers sampled oyster shells from several rings on Sapelo Island. For each shell, they inferred its season and location of harvest using oxygen isotope values in the shells’ layers. Oxygen isotopes are proportional to the temperature and salinity of the water the shell has grown in. Analyzing isotopes gives researchers two key measures: inferred water temperature, which reveals the season during which a mollusk was harvested; and a shell’s salinity, which pinpoints the location oysters were harvested from.
The findings from these analyses paint a picture of seasonally and spatially variable harvest on Sapelo Island. The research team found a different range of salinities for shells harvested in the summer versus the winter, suggesting that Ancestral Muskogean people were harvesting mollusks at certain reefs in certain seasons.
All together now
Seasonal variation in harvest location likely represents coordinated efforts within and between villages. Reefs in this area were accessed by many villages, which could have posed a problem for reef persistence. “Oysters and clams are common pool resources; everyone has access to them, and research has shown even a small community could have overharvested a reef within a few years” says Dr. Garland. However, the oyster reefs from which many villages were regularly harvesting were stable for thousands of years during this time. Since any one village could have over-exploited the reefs, Dr. Garland and his fellow researcher Dr. Thompson concluded that the villages harvesting reefs must have cooperated in order to keep reef populations stable for so long.
When they reached these conclusions, they shared them with the Muscogee Creek Nation’s Cultural and Historic Preservation Office, with whom they have a working relationship. “Here at the archaeology lab, we’ve changed how we do things in the last few years. Everything we do is in consultation or collaboration with tribal communities; this starts with research grant proposals and goes through publication,” says Dr. Garland. “We want to make sure that our work doesn’t do any harm, is incorrect, or doesn’t fit with their perspective.”
When collaborators at the Historic Preservation Office looked over these results, they told Dr. Garland that the idea of ancestral Muskogean peoples collaboratively managing shellfish harvest concurred with their understanding of Muskogean history and culture. As Dr. Garland relayed, “these villages are connected. There were kinship and social connections between villages, and they were traveling all over the place, and tied together by ceremonial feasts and gatherings made possible by the production of mollusk surplus.” Pairing a chemical data set with sociological understanding has yielded a greater understanding of ancient harvesting practices than either could have separately.
Looking to the future
Collective decisions about how to manage natural resources are not relegated to the past. Ancestral Muskogean people cooperated to sustainably harvest shellfish for thousands of years. Yet, in the last few centuries, colonial harvesting practices have decimated fisheries in the very same waters. Looking forward, then, it is important to know that there are blueprints available – examples of sustainable and cooperative ecosystem management. Such examples can guide decisions made today for the good of tomorrow.