Why is General Zaroff's island called "Ship-Trap Island"?

General Zaroff's island has been named "Ship-Trap Island" because a significant number of ships tend to wind up running into the island's rocky shores.  It is as if the island somehow can lure and trap ships and sailors.  
There is a legitimate reason for why so many ships are drawn to the island though.  General Zaroff explains to Rainsford that he intentionally tricks the ships into thinking they have safe passage through a channel.  As General Zaroff is taking Rainsford on a tour of his home, Zaroff turns on some electric lights that are located in the island's waters.  The lights indicate that a channel is present where there is actually no such channel.  The false channel lights indicate safe passage to ships; however, when a ship attempts passage, the ship runs itself into the island's rocky shore.  The ship is torn apart, and the sailors are then captured by Zaroff to participate in his sadistic game. 

"Watch! Out there!" exclaimed the general, pointing into the night. Rainsford's eyes saw only blackness, and then, as the general pressed a button, far out to sea Rainsford saw the flash of lights.
The general chuckled. "They indicate a channel," he said, "where there's none; 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."