Who is Bob Harvey in The Mysterious Island?

In Jules Verne's The Mysterious Island, Bob Harvey is the captain of the pirate ship Speedy. With a crew mostly comprised of English ex-prisoners from the penal settlement on Norfolk Island, he has raided and plundered ships throughout the South Pacific.
The Speedy arrives, by chance, at Lincoln Island, the refuge of the novel's protagonists. The latter are a group of half-a-dozen Northern prisoners in the US Civil War who have escaped from the Confederate prison in Richmond via a balloon which took a considerable detour.
The refugees, though vastly outnumbered, engage the pirates in battle, but appear to be on the verge of defeat when the pirate ship mysteriously explodes, killing all but a handful of its crew. Bob Harvey is nowhere to be found.