Something Fishy in the Site of El Collado?

Image from Guixe, Richards, & Subira "Palaeodiets of Humans and Fauna at the Spanish Mesolithic Site of El Collado," 2006: http://www.jstor.org/stable/10.1086/504170

El Collado is the largest Mesolithic site in Spain, located near the eastern coast.  Due to its location and the fact that a shell midden is nearby, people have assumed that marine resources were a huge portion of people’s diets.  However, this actually isn’t true.  Guixé, Richards, and Subirà are three scientists who analyzed the skeletons of fifteen individuals and cattle from around 7,500 BP.  Bones contain carbon and nitrogen, which break down into isotopes at a steady rate over time after the individual’s death.  The isotopes accumulate within the body at a steady rate while the individual’s alive, but the rates can change based on people’s diets.  Carnivores have more nitrogen in their bodies, because they absorb the nitrogen from the bodies of their prey, which contain more nitrogen than the plants that their prey eat (interestingly, babies that are breastfed actually present as cannibals, because they’re getting a high amount of nitrogen from their mothers).  Organisms that eat a marine diet as opposed to a terrestrial one also contain more nitrogen.  Guixé, Richards, and Subirà looked at the ratios of carbon and nitrogen isotopes in human bones, and they saw that only two people were eating a huge amount of seafood.  Everyone else was eating mostly terrestrial resources.  It could be that the Mediterranean just didn’t have as many edible fish as the Atlantic, but it seems that people were eating more land animals like cattle than marine food.