Fisherman frequently dredge up stone age (or earlier) implements from there.

Stone age ... or earlier? You mean from before the discovery of stone?!

Maybe they are talking about fossils? EG: Before humanity stuff.

And that area of the sea is still known as "Dogger" in the shipping forecast https://en.wikipedia.org/wiki/Shipping_Forecast#/media/File:...

That part of the sea as well as Doggerland itself are named afer Dogger Bank, a large sandbank that must have been some promontory on Doggerland.

Dogger Bank in turn seems to be named after a kind of Dutch fishing boat called a dogger

https://en.wikipedia.org/wiki/Dogger_Bank