Haven't actually run a cost analysis (and I'm not really sure how), so I may have been a bit premature. I seem to remember that the cattle had to be brought from quite a distance, and were being butchered on-site. They did find a lot of fish remains as well, but the amount of cattle surprised the researchers. It's just not something that was generally fed to slaves, at least not on a regular basis.
I'll try to dig up a bit more later today. Gotta run.
I wonder whether fish bones are preserved as well as cattle bones. Preservation of bodily remains seems to go well in those regions, but still, fish bones are small and can easily be displaced by storms. And shrimps and any other seafood would not even leave remains.
Im just saying, many food items would not leave remains or are less likely to leave remains then huge cattle bones.