Based on the original 'impression' that they were run over, my initial thoughwhen they said three our four found and one was missing: there was one on watch (outside) -- he was thrown off and the others were below and got mix-mastered. Of course, that's COMPLETELY SPECULATIVE.

Our course the Guadalope Island is a not that far away to the West, and I remember seeing a film on the White Sharks that migrate between ther and Hawaii....

But I agree, your thoughts on why the one wasn't found may have some related explanation to the sad event's cause.