Another early rowing reference that I think is really important --perhaps the earliest setting so far-- is one I've discovered in this article:

http://www.jstor.org/pss/895685

(I don't have access to read it all. If someone else does, perhaps they'd like to scan it for other gems.)

It refers to observations by W.J. Grayson (born 1788) of South Carolina, who "from his boyhood" --1790s or 1800s-- remembers African-American oarsmen that would bring people to Charleston. He describes their call and response canoe-rowing songs as "partly traditionary, partly improvised" and goes on to relate their incidental themes, as have the other authors.