Stories that old oyster shells tell – part 7

The following is the seventh 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

Part 7

THE GENERAL PICTURE

Oyster and other marine mollusc shells have been examined from 60 sites for this project. In addition to firmer ideas about movements of oysters between different localities in the past, and site specific information about oyster usage, in broad and brief terms, the following picture emerges about oyster exploitation in Britain.

No oyster shells seem to have been recovered from Iron Age sites. Specimens found at Owslebury in Hampshire are now believed to be incorrectly dated to that period.

Roman sites throughout the UK are renowned for the massive quantities of oysters. Contrary to assertions in the literature, no physical or documentary evidence has been found so far to indicate that the Romans introduced oyster cultivation to Britain. Although they used cultivation techniques in Italy, these would have been impractical and unnecessary in Britain. Oysters appear to have been an unexploited resource immediately prior to the Roman invasion.

The claim that oysters were transported around Britain alive in lead tanks of salt water seems also to be highly unlikely and immensely impractical. Oysters will remain fresh for up to ten days if kept cool and packed closely to prevent opening of the valves. The transport system was excellent by road, river and sea. Oysters may have been packed tight inside British made pots that were marketed to the Romans – black burnished ware pottery manufactured on the southern shores of Poole Harbour in Dorset, adjacent to abundant natural oyster beds, was sent as far afield as Housesteads on Hadrian’s Wall.

The large average oyster size for the period may reflect an abundance of mature specimens, a preference for eating larger oyster meats than we select today, as well as a rapid growth rate.

Saxon sites also produce lots of oysters but these are mostly near the coast or with easy access by river to the coast. Deterioration of the roads with the exit of the invaders and poorer organisation meant that oysters could not be sent far. Average size is slightly but significantly smaller than those from Roman sites. To date there is still no evidence for farming or cultivation of oysters.

By the Medieval period, oysters were far more widely distributed across the country. They were also very noticeably smaller. Their size tended not to be the result of selecting less mature specimens but rather a much slower growth rate. This could be attributed to temperature changes but is also likely to be a direct result of oyster relaying and storage activities. Documentary records are made about the ownership of oyster beds and oyster fishing rights. Oysters that are re-laid inter-tidally and periodically exposed at low tides cease to grow whilst out of water. Simultaneously they learn to keep the valves tight shut when exposed to the air. This ability means that they stay alive for longer when traded and dispatched. Improved longevity in keeping fresh means that oysters can be sent greater distances. The greater numbers of oysters found on coastal sites reflects their easy availability and indicates that they were a staple of the diet. The smaller numbers of oysters found at inland sites suggests that the cost of transporting them made them an occasional and luxury item for these people.

Not many oyster specimens of Post-medieval date were made available for study, so conclusions are few. The shells were smaller than in earlier periods.

The Modern period, for current purposes, is taken as including the 19th century onwards. This saw the advent of the railways and with them a cheap way of selling oysters to the masses all over the country. It was a boom time for oystermen and more and more boats went out to fish the beds. Holding pits on the shore became commonplace to store the catches before marketing. Prices of oysters plunged. They became the food of the common people everywhere, not just those living on the coast. They were so cheap that London apprentices complained of their monotonous diet of oysters and salmon.

Eventually, the oyster beds were over-fished and stocks became depleted. Efforts were made to cultivate oysters and breed foreign species. All attempts failed. The final blow to the incredibly successful oyster industry of the 19th and early 20th centuries came with massive extinctions of beds in the 1920 – thought to result from extreme cold weather and disease.

A few natural beds of oysters survived. Oysters became a luxury item on the menu again. A second catastrophe in the form of Bonamia disease decimated remaining stocks in the 1970s. This time modern technology came to the rescue of the British oyster industry by breeding oyster spat of both Ostrea edulis and Crassostrea gigas in the laboratory so that beds could be restocked. Oyster farming today with its net bags of brood oysters and floating platforms would not be recognised by our predecessors. Their methods were undoubtedly simpler but harder and we still have much to find out about them.

In the next and final part of this brief summary of the research I’ve carried out on oyster shells from archaeological deposits over an extended period of time, Part 8, looks at possibilities for future studies of this subject and provides a selection of references of work cited in this account.

 

N.B. Please leave a comment or e-mail me directly on winderjssc@aol.com 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.

© Jessica Winder and Jessica’s Nature Blog, 2010. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved

Stories that old oyster shells tell – part 6

 

The following is the sixth 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

Part 6

EXPLOITATION MODELS – THE EVIDENCE CONSIDERED AS A WHOLE

The combination of features, from size and shape to epibiont and man-made damage, provides not only a standardised way of describing a sample of shells by giving it a unique identifier but also supplies a means of addressing some of the questions posed by archaeologists regarding the point of origin of the shellfish and the mode of its exploitation. A series of theoretical models has been drawn up that identify which types of evidence from the shells are indicative of the different aspects of oyster bed location and level of exploitation (Winder 1993 Chapter 11 The conclusions and discussion: Levels of oyster exploitation pp 281- 304). These models bring together ideas about which combinations of features in archaeological oyster shells, associated species, and excavated material structures might be useful for interpretation.

Five theoretical exploitation models are described but in reality there would be a continuum of gradually intensifying activities from sporadic hand-collection from natural intertidal beds to full-scale commercial cultivation and marketing of oysters. Each element of data recorded from the oyster shells and the site can potentially contribute to our understanding of the particular type of environment in which they lived, and the level of effort involved in their exploitation. For example, infestation evidence could be used to suggest the locality of the bed, whether the bed was inter-tidal littoral or shallow sub-littoral, harder or softer substrate and also the degree of salinity. Size distributions may reflect growth rate, recruitment variability, selection preferences, and survival rates. The diagram in Figure 5 shows as an example Model 1 which is for sporadic hand collection from natural beds. 

FIGURE 5 

The conceptual models described above and comparisons of size and infestation have been used to interpret the data from archaeological oysters and suggest where and how this shellfish was exploited. What can we now say about eating oysters in the past based on this archaeological evidence? This research has started to give a clearer picture about the way people have exploited oysters over the last two thousand years in Great Britain, confirmed some ideas previously held, and refuted others. It is a developing methodology that will help answer some of the questions posed by archaeologists.

Next, Part 7 will finally pull together some of the conclusions that have been enabled by the application of the methods described earlier and the results obtained from the examination of over 30,000 old archaeological oyster shells.

 

N.B. Please leave a comment or e-mail me directly on winderjssc@aol.com 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.

© Jessica Winder and Jessica’s Nature Blog, 2010. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved

Stories that old oyster shells tell – part 5

   

The following is the fifth 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

Part 5

Infestation differences

Differences in the types of evidence for encrusting or infesting epibiont organisms in oyster shells closely relates to the natural conditions in which the oyster was growing – such as the depth of water, the substrate and the geographical location. Principal Component Analysis (PCA) was used initially to compare the sum total of all recorded characteristics of an oyster shell sample. However, PCA proved most useful in differentiating oysters from different regions based on the infestation characteristics (Winder 2002).

 

FIGURE 4 

Figure 4 gives the result of a PCA of infestation in Roman oyster samples and demonstrates regional differences. Each coloured symbol on the chart represents a sample from a named site. It is only necessary to note for present purposes that the chart shows samples segregated mainly into two groups. Those from Essex and Suffolk are grouped together on the left and those from Dorset, Hampshire and Wiltshire to the right. Samples denoted ‘Shir for The Shires excavation in Leicester, and ‘Pud’ from Pudding Lane in London are included in the grouping of samples known to have originated in East Anglia and indicating that oysters at these inland sites were obtained from that part of the country.

The same marked differentiation can be seen for PCAs for other periods as well. The organisms that seem primarily (but not exclusively) to account for this regional differentiation of oysters from the South Coast compared with the East Coast are polychaete worms of the Polydora genus. These worms leave characteristic burrows in the shells. Polydora ciliata (Johnston) seems to be ubiquitous while the larger species Polydora hoplura Claparède appears to be restricted to southern waters. PCA seems a promising approach for pinpointing the source of oyster samples and will be developed.

 

N.B. Please leave a comment or e-mail me directly on winderjssc@aol.com 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.

© Jessica Winder and Jessica’s Nature Blog, 2010. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved

Stories that old oyster shells tell – part 4

 

The following is the fourth 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

Part 4

A FEW RESULTS

Some results of the analyses of the two main contributors to variability in the shells of Ostrea edulis L. are presented here. These relate first to size and, in the following Part 5, evidence of infestation and encrustation by epibionts.

Size differences

The size of oyster shells recovered from ancient sites results from a combination of factors: natural environment, genetics, and human influence. Examining size can potentially help to distinguish, for example, between oysters originating from different localities or subject to varying fishing practices. Measurements of more than 30,000 oyster shells were used initially and comparisons between the samples made by parametric and non-parametric statistical tests for various categories of sample (Winder 1993 Chapter 9 Intersite variation in size of oyster shells). These categories included samples from different geographical regions, inland and coastal sites, urban and rural sites, and various historical periods.

 FIGURE 3

Comparisons of size for broadly defined historical periods reveal interesting variations in mean size between the Roman, Saxon, Medieval, Post-medieval and Modern oyster shells. This appears to indicate statistically significant temporal differences in the average size of oyster shells. Roman shells are largest but size decreases progressively through successive periods until a recovery to almost Roman dimensions in the Modern period. The data will be reworked using more sophisticated computer software and the much larger database that has been acquired since this analysis was first completed.

Figure 3 is just a simple bar chart representation of the differences in size of oyster shells through time based on the original analysis. There are two bars for each period and these indicate the overall size for left  (blue bar) and right (red bar) valves. The sizes of the two types of shell valves are always different even for the same individual oyster. The right flat valve is smaller than the left and sits somewhat within the shallow saucer shape formed by the left valve. The perimeter of the right valve in life frequently has a flexible new growth of shell that extends to meet the edge of the left shell. In right oyster shells recovered from archaeological excavations this fragile outer margin is absent.

The final bar of the above chart, which represents results for Modern oysters, lacks figures for right valves. The reason for this is that the majority of the measurements in this category were taken from fresh living specimens of oyster in which it was not possible to determine with accuracy the dimensions of the in situ, almost embedded, right shells. The maximum diameter dimensions of the entire oyster were recorded in living specimens. Right valve measurements of living oysters would not be directly comparable in every instance with right valves of archaeological specimens.

In the next instalment, Part 5 will discuss some of the results from analysis of infestation characteristics in archaeological oyster shells.

 

N.B. Please leave a comment or e-mail me directly on winderjssc@aol.com 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.

© Jessica Winder and Jessica’s Nature Blog, 2010. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved

Stories that old oyster shells tell – part 3

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

Part 3

 

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 winderjssc@aol.com 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.

© Jessica Winder and Jessica’s Nature Blog, 2010. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved

Stories that old oyster shells tell – part 1

Regular visitors to Jessica’s Nature Blog will no doubt have noticed the frequency with which photographs and articles are posted about the many variations to be seen in the shells of the British Native, Flat, or European Oyster, Ostrea edulis Linnaeus. Variation in oyster shells has been a subject that has interested me for many years - mainly because of its implication for the understanding of this particular marine mollusc in archaeological contexts. You can see these previous oyster shell posts by clicking here for the Oyster Variations category.

The following is the first instalment of an 8 part summary of the work I have been undertaking on Flat Oyster shell specimens from archaeological and present day contexts under the title Two thousand years of eating oysters in the UK: an archaeological perspective. The contents of these parts will be as follows:

Part 1 - Introduction and Background to the research

Part 2 – Methods

Part 3Caveats to analyses of the archaeological data

Part 4 – A few results: Size differences

Part 5 – A few results: Infestation differences

Part 6 – Exploitation models: the evidence considered as a whole

Part 7 – The general picture: Roman, Medieval, and Modern

Part 8 – Future work and References

 

Two thousand years of eating oysters in the UK:

an archaeological perspective

Part 1 

INTRODUCTION

Easily observable features in oyster shells from archaeological excavations can provide important evidence of where the oysters came from and the way they were exploited by man.

The shells of the European flat oyster (Ostrea edulis L.) are immensely variable and reflect the natural environment in which the mollusc was living as well as the human activities associated with their collection, their use as food, and the method of their disposal. There have been extensive studies of large oyster middens from early periods worldwide, such as those at Ertebölle in Denmark, Mesolithic sites in Scotland, and later with the colonial period in the Americas. However, relatively little work has been undertaken on the more recent archaeological oyster deposits of the last two thousand years in the United Kingdom where mostly the quantities of shell are smaller and the sites can be inland as well as coastal, and both urban and rural. 

This article gives a very brief overview of the methods and preliminary results of investigations that have been made into oysters from excavations of these relatively recent archaeological sites in Britain – using observations of their macroscopic characteristics. It is based on a series of published and unpublished reports made to archaeological organisations, and also the doctoral thesis:  A study of the variation in oyster shells from archaeological sites and a discussion of oyster exploitation (Winder 1993).

BACKGROUND TO THE RESEARCH

Awareness of this potential research opportunity was raised in the 1970’s when a surge of construction development and its associated archaeological investigation uncovered large quantities of marine mollusc shells. An example of this was the excavation of Saxon Hamwic in Southampton where vast numbers of marine shells were recovered, mainly oyster, from domestic rubbish pits. The archaeologists had hundreds of large museum boxes full of mud-caked shells in store and wanted to know what to do with them.

Had these shells, they wanted to know, any potential for site interpretation? If so, could they be used to indicate how important marine molluscs were in the diet of the community? Where did the shellfish come from? Was it possible to establish the locations being fished in order to understand how far afield people were going for food and to suggest trade links and routes? How intensively were the shellfish beds being exploited – how much effort and organisation was invested in the activity?

Another aspect which intrigued archaeologists was whether some degree of oyster cultivation had been taking place. Were the oysters fished from natural (wild) beds or were they farmed, cultivated and subjected to more commercially orientated activities? It had always been assumed by historians that the Romans introduced oyster cultivation to Britain but could this be substantiated from the archaeological record?

The problem for the archaeo-malacologist is to discover what actually survives in the oyster shells that can possibly help to answer the questions posed by the archaeologists about the way people have exploited oysters in the past. Much of what is already known about the oyster and man relationship can be found in the general literature, particularly accounts from the 19th and early 20th century discussing eating, fishing and farming oysters. Despite some serious gaps in the periods covered, and not a few misunderstandings, this older literature contains some very useful information – including a quotation from the Roman poet Lucilius who said:

When I but see the oyster’s shell,

I look and recognise the river, marsh or mud,

Where it was raised.”

It is clear from allusions in the literature that, in fresh oyster shells at least, it is possible to observe variations that could be attributed to the place of origin. This idea was developed by Alfred Bell in the Essex Naturalist of 1921 where he meticulously described variations of British oyster shell shape, ascribing sub-species and variety names to specimens from different locations. Unfortunately, it seems likely that his descriptions may have been based on just a single specimen in some cases.

So, the task in hand was first to decide which particular surviving characters in the oyster shells might be useful in answering the questions posed by the archaeologists; and second, how to analyse the recorded information in a meaningful scientific way. This will be discussed next, in Part 2 of this account, which will briefly describe the basic methods used in the research.

  

N.B. Please leave a comment or e-mail me directly on winderjssc@aol.com 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.

© Jessica Winder and Jessica’s Nature Blog, 2010. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved