Oh come on, this item has been in the sea for over a year, gone through how many storms? been colliding with how much other debris and general flotsam? Collided with how many ships? been washed up on at least one shore.
How can any damage be identified as having been caused at the time of the incident
Actually you can clearly distinguish between crash related damage and anything that happened in the ocean, even after the time in the water. These are carbon composite parts and they fail in a brittle nature. Unlike aluminium parts they do not bend. Either they break or they do not.
Impact with a marine object would probably cause crushing at a specific location rather than the linear separation of the entire trailing edge as evident in the photographs I have seen. It would take an exceptional coincidence of circumstances to separate the trailing edge in anything other than a high energy crash related impact, not even if the impact was with a speeding marine vessel on a free floating flaperon.
Even if an intelligent and composite technology knowledgeably terrorist (now there's an oxymoron) actually set out to intentionally break away the trailing edge to confuse the investigators, given the strength of composite materials he would need either superhuman strength or some very sophisticated test equipment to produce the identical failure surface that would be created by an ocean impact.
Gnawing by great white sharks could easily be assessed by Mick Fanning.
It is possible to clearly distinguish between compression and tension failures in composites. I would expect that ocean impact would result in one surface exhibiting tension failure and the other exhibiting compression failure, and which surface exhibits the tension or compression will depend on if the aircraft was in normal flight mode or in inverted flight. An edge-on impact would result in shear failures which again could be identified by any competent composites failure forensics specialist.
The truth will be evident from the forensic examination of the composite fracture surfaces, and if it is definitively found to be attributable to ocean exposure alone or to terrorist induced deception, then I would be prepared to expose the what is left of the family jewels and walk down the beach at Surfer's Paradise backwards towards the great white sharks if Mick Fanning joins me.
Regards
Blakmax