Santander, February 19th-22nd 2008 - Aranzadi

194
CATHERINE DUPONT
hence these perforations could not have been
caused by trowels. Furthermore, these holes were
covered with sediment, which makes it possible to
reject their recent origin. In total, 20 perforated valves
were observed. In spite of this limited number
compared to the 3724 observed oyster valves,
they could suggest that they were the result of
tools used to gather the oysters.
Among these 20 valves, 19 are right and only
one is left; the latter was joined with a right perforated
valve (Fig. 3-F). This whole specimen seems
to correspond to the action of a tool which could
have pierced the entire thickness of the oyster. The
predominance of perforations on right valves is
confirming evidence for their creation during
gathering. When the oyster spat develops on a
support, it is the left valve which takes a more or
less concave shape that conforms to the shape of
the substrate on which it is adhered. The right
valve, which closes the bivalve, thus seems more
vulnerable to the action of a collection tool.
In order to have additional information on the
tool or the tools used, these perforations have been
analysed according to their shape and dimensions
(Fig. 4). The dimension measured is the biggest
opening of perforations. The confidence intervals
make it possible, despite everything else, to take
into account the variability of dimensions of perforations
for each shape. This confidence interval is
close to the extreme values of the size of the perforations
because of the small number of perforations.
It shows that the smallest perforations have
rather round shapes while the largest more angular.
These differences can correspond to different
degrees of force applied when driving in the tool.
The teeth of the tool could have a pointed tip with a
more angular shape at the base.
However, the presence of both round and
angular impacts (Fig. 3-G and H) does not make it
possible to exclude the use of two tools: one with
a rounded tip, the other with a broader angular
shape tooth.
Several tools are used to exploit oysters: the
dredger, the rake, double rakes and the mortise
axe (Fig. 5, Clerc 1828). The mortise axe and the
long handled rakes are intended for use in the
intertidal zone.
The low frequency of stigmata observed could
correspond to raking of the marine bottom using
various kinds of less destructive rakes rather than
the mortise axe which would perhaps cause more
perforations.
3. ACTIVITIES LINKED TO THE EXPLOITATION OF
OYSTER MEAT
3.1. The selection of opened oysters
Opening scars have been observed on 59% of
the right valves and 67% of the left ones. The most
frequent scar observed is a notch which is precisely
8 mm wide at the edge of the oyster opposite
the hinge. The opening movement with a knife
seems to be standardized.
Figure 4. Measurement of the larger dimension of perforations observed on oysters according to the shape of the stigmata (C. Dupont)
MUNIBE Suplemento - Gehigarria 31, 2010
S.C. Aranzadi. Z.E. Donostia/San Sebastián