Yup, the author is an anthropologist. Who else could create such a strange depiction of human behavior stretched to its limits? Or, better stated, who else would know enough about human behavior to care to do so?
I am a bit puzzled by the number of languages this book has been translated into from the Catalan. I mean, it isn't THAT good. Any book involving monsters is going to turn off half (if not more) of the world's population. The other half may be turned off by all the human-alien sex (what's the point of that, again?). Anybody who is left is still going to be disturbed reading about this poor man stuck on an island surrounded by sea-dwelling flesh-eaters, fighting with his "roomie", and trying to come to some understanding or resolution that will save him.
I did like the ending, as it points to the cyclical nature of man and any civilization it builds. I was okay with the book leaving you hanging, wondering if the cycle does continue exactly the same way or if this particular man has learned enough to not fall prey to his own thoughts and emotions, much less the monsters on the outside.