The following is the third instalment of an 8 part summary of the work I have been undertaking on British Native or European Flat Oyster shell specimens from archaeological and present day contexts. You can see previous posts about the shells of Ostrea edulis Linnaeus by clicking here for the Oyster Variations category.
Two thousand years of eating oysters in the UK:
an archaeological perspective
CAVEATS TO ANALYSES OF THE ARCHAEOLOGICAL DATA
There are many challenges to working with archaeological oyster shells. There are possible biases to the material that would affect the analysis and interpretation of the data. Among the questions we need to ask is how representative are the examined samples of the potentially available pool of archaeological oyster material?
In the case of the extensive Saxo-Norman oyster heaps on Poole waterfront (Winder 1992; Horsey and Winder 1991) and the nearby 12th century middens at Ower (Winder 1991)) on the southern shore of the Poole Harbour, neither are likely to have been permanent habitation sites. The shells excavated from these sites are thought to result from processing of the meats prior to marketing with the shells being discarded on the spot; so they would probably represent the entirety of the catch.
Whereas, on sites such as Elms Farm in Essex (Winder 2000) near to the head of the Blackwater estuary famed for its oyster beds, the smaller numbers of shells remaining on site from Roman and early Saxon phases may well indicate that the majority of the catch was being marketed in the shell. Oyster shells are very bulky and can present a disposal problem when fishing for and eating oysters is an important part of community life; so an alternative possibility to consider, is that the shells may have been recycled. They can, for example, be returned to the sea bed as cultch on which oyster spat can settle; used to fertilise (lime) the fields; used in the manufacture of lime; crushed for chicken feed, shell-tempered pottery, medicines and cosmetics; used as hardcore, for paths and yard surfaces; and used as mortar for stone work.
How representative are the shells from an individual site of the original incoming samples to that site – both in quality and quantity? Moorgate and Coleman Street excavations in London (Winder 1987) of 11-12th century domestic rubbish pits uncovered strikingly different shells in different pits. One contained poor quality oysters of very small and very large size, while the other had all the better quality shells of the optimal mid-size range. It is easy to see how erroneous conclusions could have been drawn if the specimens from only one pit had been selected for analysis.
Has there been an excavation bias with only the larger or intact shells being retained? We need to know the criteria for retrieval. And subsequently, what was the rationale for selecting samples for analysis? How much reliance can be placed on comparisons of archaeological oyster shells with samples of modern material from known locations? Comparisons of this sort would be very informative. However, there have been substantial losses of natural oyster beds in Great Britain, plus coastline and sea-level changes, and possible contamination of native oyster beds by interbreeding with imported oysters from home and abroad.
Finally, the taphonomic history of the shells, soil conditions and disposal methods will affect the chemical and mechanical wear on the shells. There is randomness to shell survival and recovery as well as to the process of shells being made available for study. All of these factors have to be considered and they place restraints on the interpretations based on the shells. Additionally, there can never be enough samples. With this awareness, the analysis of the data was carried out.
In the next instalment, Part 4 will describe some of the results obtained from analyses of size and infestation characters in the archaeological oyster shells.
N.B. Please leave a comment or e-mail me directly on firstname.lastname@example.org if you would like to ask any questions or to have a free copy of the complete article sent to you as a pdf file. This article is just a very brief summary of my archaeological oyster research. A small selection of references to publications and reports will be provided with the article.
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