I've read sharks see the cables as potential (ha!) prey due to slight EMF leakage. They chew on them damaging them. Not the fiber optic ones of course.
All trans-oceanic cables carry an electric current in addition to light in fiber(s). Electricity is what powers the optical amplifiers of which there needs to be one every hundred or so kilometers.
For short-ish cables (a couple hundred kilometers), driving the amplifiers via light (interestingly this can be done from both the data-sending and receiving end!) is possible, but not for trans-oceanic distances.
