Elephant seals don't use echolocation the way whales and dolphins do, but no one knows exactly how they navigate or hunt. Environmental impact on their main prey would certainly ripple out to them. The prey have to do well in order for their predators to succeed.
Life in the ocean is harsh. The increasing noise is a serious problem for marine mammals of all kinds. Garbage causes deadly entanglements. This seal, in the upper right of the photo, has been on the beach for several days, with a green plastic rope cutting into her neck. She has remained close to other seals, making a rescue impossible. If she gets away from the group, Marine Mammal Center rescuers may be able to get to her and clip the plastic off, freeing her.