Complex sentence: There were a total of nine shipwrecks leaving marooned castaways in the New Zealand sub-antarctic between 1833 and 1908, some of whose lives were saved by the existence of the castaway depots.
Split into simpler sentences: There were a total of nine shipwrecks leaving marooned castaways in the New Zealand sub-antarctic between 1833 and 1908. Some survivors' lives were saved by the existence of the castaway depots.