Polar bears eat any dang thing they please, because they are bears.
End of discussion. There’ve been dolphins in the arctic for a long, long time!
Shouldn't them bears be eating vegetarian now, with all them plants growing on the ice-denuded bits of land in the Arctic Circle-ish region?
In reality, the dolphins probably had been slow from feasting on the cornucopia of seafood delight up North, and the Polar bears were not only faster, but hungrier.