I think you have the backwards -- sharks aren't attracted to copper cables.. but are attracted to undersea fiber optic cables.. because they carry high voltage power (for the undersea repeaters), which emits an electromagnetic field that attracts the sharks:
I stand corrected, forgot about the power cables I know sharks were attracted to the EM field around the old transatlantic phone and telegraph wires. Well at least it will be a good reason for an outage.