Global connect (the company that owns and operates most data cables in the Baltic sea) is running tests with tamper detecting cables. They say they will be able to detect a whale at a distance of 80 kilometers. I assume the whale is just used as an example to demonstrate its sensitivity, since whales haven't been implicated in any of the previous cable breaks.
Swedish: https://www.svt.se/nyheter/inrikes/ljusstrale-genom-kablar-k...