The melody is described in Roberton's Songs of the Isles as a traditional Gaelic tune, probably titled "Lochaber".
[1] The tune was part of an old Gaelic song, "Òran na Comhachaig" (the 'Creag Ghuanach' portion); from Brae Lochaber.
[2][failed verification] The song describes fishermen sailing homeward to the isle of Mingulay where their families wait.
Wives are waiting on the bank, or Looking seaward from the heather; Pull her round boys!
and we'll anchor, Ere the sun sets at Mingulay.