jcjeant - that's right - the great unknown in all of this is the behavior of composite structures under atypical stresses - there are many competing models, often mutually wildly divergent, all highly non-linear, of composite failure under stress.
sd666 - not quite sure what you mean about anchoring, but the water moves as a body, any flotsam would be well inside the boundary layer of air at the water interface, and any islands of debris, large and small, would tend to remain together until dispersed by divergent currents of water, not air. The Perpignan fin was just the largest piece in a huge swarm of debris, and I would have expected something similar here.