An ecological interpretation of Mesolithic shellfish remains on the island of Oronsay, Inner Hebrides
The island of Oronsay in the Inner Hebrides contains five Late Mesolithic shell middens. This research uses ecological investigations on limpets (Patella spp.), periwinkles (Littorina littorea L.) and dogwhelks (Nucella lapillus L.) from the present Oronsay coast to aid an interpretation of the shellfish collection strategies of the Mesolithic hunter-gatherer populations, and to establish. the relative importance of the three shellfish species in their diet. Section A is devoted to ecological examinations of contemporary limpets, periwinkles and dogwhelks, and in Section B this information is applied to the midden shellfish. In chapter an examination is made of previous research into selected aspects of the ecology of the three species, which forms a necessary basis for the present research. In each species an examination is made into studies concerning population dynamics (reproduction and mortality), the distribution of the animals over the shore, growth, and the physiological ecology of body and shell development. Chapter 2 examines seasonal meat weight changes (ie body weights) in animals from an area of the present Oronsay coast at different tidal levels over a full year. For chapter 3 further fieldwork was carried out around the Oronsay coastline to examine the difference in population structure of the three species in varying coastal environments, and at different tidal levels. Attention was paid to variations in size in each of the species, and their relative proportions between sample sites. An examination was also made of shape distribution of limpets at different tidal levels. Chapter 4 makes comparisons between present Oronsay coastal environments and those of the Mesolithic, with relation to coastal morphology and exposure, and sea temperature, to assess the validity of using contemporary data to interpret activities on Mesolithic Oronsay. Section B begins with a brief synopsis of the main approaches that have previously been adopted in midden studies. Chapter 6 then uses information gained in chapter 3 to explain the size distribution of each species in the middens, the shape distribution of the midden limpets, and the relative proportions of the three species, in terms of the collection strategies of the midden dwellers. Interactions xix between the human predators and the shellfish populations will be reflected in the size-frequency structure of the midden shellfish from the base to the top of the middens. From sample columns in each midden an assessment is made of the intensity and periodicity of exploitation, and of the relative importance of each of the three shellfish species. Chapter 7 uses data from chapter 2 to reconstruct the relative proportions of meat weight provided by each shellfish species in the middens. Account is taken both of shellfish size, tidal position, and the varying amounts of meat which may have been obtained at different seasons. Seasonal changes in body weight are demonstrated in limpets, periwinkles and dogwhelks from the present Oronsay coast, which are related to their reproductive cycles and feeding intensities. When this information is applied to the midden shells, at each possible collection season limpets are shown to provide around 90% of the shellfish meat weight. On the modern coast the relative proportions of the three species vary greatly from different shore environments, yet in the middens there is a much greater uniformity in the relative numbers of the three species. There are no major changes in species composition or size upward through the middens, and it is argued that this indicates a fairly low intensity, regular exploitation.