There are several reasons that an island may best serve General Zaroff for his evil purposes. First, Ship-Trap Island is a remote and "God-forsaken place," generally off the beaten track for most ships. Secondly, being an island, there is little chance to escape, since the waters are probably shark-infested and there is no mention of a nearby isle. But most importantly, Ship-Trap Island has its own built-in advantage for Zaroff. The dangerous reefs and
"... giant rocks with razor edges crouch like a sea monster with wide-open jaws. They can crush a ship as easily as I crush this nut."
Zaroff has installed channel lights "where there's none." By turning the lights on or off, he can lure unsuspecting ships to the waters, shipwrecking the stranded sailors on the island. It is those sailors that he uses for his special kind of hunt.