Hydroclimatic conditions and fishing practices at Late Paleolithic Makhadma 4 (Egypt) inferred from stable isotope analysis of otoliths

The late Paleolithic site of Makhadma 4, located along the Nile River in Upper Egypt, yielded an important ichthyofauna characterized by a very high proportion of tilapia (Oreochromis niloticus). We used isotopic analysis (d18O) of well-preserved otoliths (“ear stones”) of tilapia to reconstruct the former hydrological conditions, as well as the fishing strategies of the site's inhabitants. Otoliths from two modern fish captured in the Nile River near Esna were also examined to test how accurately tilapia otoliths reflect their ambient environment. All otoliths were sequentially micromilled to recover high resolution isotopic profiles along the main growth axis. Comparison of the modern otolith profiles with environmental data shows that tilapia d18O values record seasonal variations of the modern Nile hydroclimate but that their values are offset. The archaeological otoliths record very large intraindividual cyclical variations in d18O values, with relatively consistent amplitude, as well as very high seasonal maximum values (up to þ8.3‰), compared with the modern otoliths. The hydrological regime of the water body in which the archaeological fish lived was characterized by a reduced Nile water inflow that could not negate the effect of local evaporation during spring. The reconstructed hydrological conditions are in accordance with a new model of Nilotic behavior that assumes the creation of lakes by damming of the Nile as a result of a high eolian activity during hyper-arid periods of the Late Pleistocene. Although large seasonal evaporation may have resulted in a severe seasonal reduction in the lake's volume and extent, the lake was, nevertheless, maintained for several years. Cyclic variations in otolith d18O values permit reconstruction of the period of the hydrological cycle during which the fish were captured. Fishing of young individuals occurred mostly after the maximum input of inflow water from the Nile, when evaporitic conditions were at their lowest, i.e. during fall.

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