To come back to the original question, "We have fed our seas" has been recorded by Louis Killen (A Seaman's Garland, KnockOut! KO04) and by John Roberts (Naulakha Redux, Golden Hind GHM-104). "Poor Old Horse" in New York City (Heather Wood, David Jones & Tom Gibney) sing it, but I don't think they've recorded it yet.
And I don't know about it being on "numerous Peter Bellamy recordings" unless you followed him around with a tape recorder. It _is_ on Wake The Vaulted Echoes, it's _not_ on Mr Bellamy, Mr Kipling And The Tradition.