Trying to understand cetacean mortality is a tricky thing. They may never know if there is a common factor in these deaths or not. One note, I’ve been working with marine mammals in Hawaii for over a decade and this year has seen a drop in stranding deaths along with a drop in entanglements. So quite a difference from one ocean to another.
Another note, I’ve seen thousands of humpback whales and I’ve never seen one 60 feet long. 50 is generally considered the maximum.