As a molecular biologist, I would like someone to tell me how DNA evidence could be found for propeller injuries or nets. Way down in the story this is one of the possibilities. And actually in my opinion one of the better ones.
DNA evidence will always find DNA from something. That doesn’t mean that “something” had anything to do with the death. Just a few seal cell would have given positive results in all likelihood.
BTW all the bar jokes really are funny. But I also think a healthy dolphin could kick a seals ace. :-)
Bob