Santander, February 19th-22nd 2008 - Aranzadi

A large-scale exploitation of oysters during the Middle Ages at Beauvoir-sur-Mer (France)
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Gruet and Prigent 1986, Soret 1985, Verger 1968,
Rousseau 1963, Baudoin 1912). The one at Saint-
Michel-en-L’Herm is the best known because it has
been exploited from 1924 to 1964 to improve soils
and construct roads (Verger 2005). Its volume has
been estimated between 200 000 and 600 000m 3
(Verger 2005). This shell midden presents other
common points with the one at Beauvoir-sur-Mer: it
is located on muddy Flandrian sediment, its shape
seems to follow the shape of an old waterway and
it is known to have been formed between the 11 th
and the 13 th centuries (Verger 2005). The stratigraphic
position of the Bourgneuf-en-Retz is known
thanks to the cleaning out of a drain. Its position
above the muddy Flandrian sediment is the element
that encourages authors to attribute this
deposit to the same period as the ones at Beauvoirsur-Mer
and Saint-Michel-en-L’Herm (Verger 2005).
The one at Champagné-les-Marais is only known
by prospection and there is no information about
the chronology of its formation.
The knowledge of the deposit at the village of
Langon is recent and has been excavated (M.L.
Hervé dir. / INRAP) and studied since the first version
of this paper (Dupont and Bougeant 2008). It is
the first archaeological site with such an accumulation
of oysters attributed to the Roman period (1 to
125 AD). Its common points with the one at
Beauvoir-sur-Mer are its localization at the margin of
an old marsh, a shell midden composed exclusively
of flat oysters and the presence of joined shells.
There are also references to more recent accumulations
such as those at Granville or Cancale
until the 18 th century. For example the ones at
Granville were approximately 300 metres long by
200 metres wide and 2 to 3 metres high in 1830
(Levesque 1982).
In the past, several of these deposits of oysters
were attributed to natural accumulations because
of the presence of many joined valves. However,
this observation is not incompatible with the opening
of oysters and an anthropic origin.
The excavation took place in 1984, managed by
N. Rouzeau, during which 65 kg of oysters were
extracted individually by hand from the sediment.
Some shells were joined while others were not. All
the shells found were examined before and after
washing above a column of 2mm and 0.5mm sieves.
As mentioned before, scientific interest in shells
is new in France and so this archaeological site,
mainly composed of shells, did not form the subject
of a report in the 1980s. This lack of information contrasts
with what we have obtained from the shells.
The position of the muscular impression allows
for the determination of lateralization of the valves.
All the fragments which could not be lateralized
were counted when their dimension was greater
than 0.5cm. Of the 5673 counted remains, 1919
were right valves and 1814 were left ones. The
minimum number of individuals (MNI) of oysters
represented in the studied sample is thus 1919.
Our primary goal was to understand how these
oysters were exploited. We therefore observed and
recorded the stigmata of both associated marine
organisms and the tools used by men. For the
associated marine organisms, stigmata consist of
typical perforations (single or in network) or calcareous
tubes. The stigmata linked to tools used by
men are notches, breaks or scratching. Biometric
data were recorded in order to know if the oysters
have been selected during gathering as well as
during extraction of the meat. Other parameters,
such as the size of the oysters opened and the proportion
of joined valves, allow us to define the level
of specialisation of oyster exploitation.
2. THE GATHERING OF OYSTERS
2.1. Selection of oysters during gathering
The distribution of the height of right and left
valves for all oysters sampled in the archaeological
deposit is shown in figure 2a. This diagram shows
that all sizes of oysters are represented in the
deposit: both the small and the big ones have
been carried to the site.
The presence of joined valves can be linked to
the transport of live oysters at Beauvoir-sur-Mer. In
figure 2b, only the joined oysters of the shell midden
are shown. The mean height is 54 mm for the
right valves and 60 mm for the left valves. These
values are the same as those obtained for all oysters
and further reinforce the interpretation that
both small and large live oysters were gathered
and carried onto the site.
2.2. The marine animal-life associated with oysters:
a view of the environment exploited
To know how oysters have been gathered it is
important to know the characteristics of the environment
where they developed. The endofauna
and epifauna associated with the oysters give an
indirect idea. Some oysters were still aggregated
together in the archaeological deposit (Table 1).
When they do not show traits of death (stigmata of
marine organisms attachments inside the valves,
polished aspect of the valves), they have been
MUNIBE Suplemento - Gehigarria 31, 2010
S.C. Aranzadi. Z.E. Donostia/San Sebastián