The group was shipwrecked, surviving on a turtle and drinking their own urine. The victim, Richard Parker, was apparently in a coma. Despite these mitigating circumstances, the two defendants, Dudley and Stephens, were sentenced to six months each in prison.
My assumption is that even if the victim and defendants weren't British citizens (or subjects) the case would still have fallen under British jurisdiction, whereas if the same incident had occurred on a boat registered to a different nation, Britain would have to rely on the courts of that country to interpret their own laws on the matter.
I suppose it's possible that another country could have in its laws a defence of necessity that was applicable to that precise situation, and I don't know how double-jeopardy rules and extradition treaties interact with the nationality or passive personality principles of personal jurisdiction:
https://en.wikipedia.org/wiki/Personal_jurisdiction#Internat...