Gord usually mentions that he was commissioned to write the song for a tv special/documentary and I recall it was him whistling years ago but don't remember him saying National Geographic.
He doesn't whistle anymore (the pucker gave out!) but perhaps a recorded whistle is used and Mike H. plays it on his keyboard or Mike plays it himself and then other times the audience sometimes helps out.
checking National Geographic website finds no mention of this show.
from MSN movies:
the 54 minute movie in 1981 had Jason Robards as the narrator:
Synopsis
In this documentary on seafaring in the late 19th and early 20th centuries, the weathered crews who sailed from New York to San Francisco come alive again. Focusing on the dangerous and often fatal voyage around Cape Horn in South America, the film goes back in time using previously unseen, 1920s footage. The story moves from the empty graves of sailors lost at sea to the hulks of shipwrecks in the Falkland Islands. As a graphic example of the hazards of this long journey, the ill-fated maiden voyage of the sunken "St. Mary" is recounted in detail. The theme of unflagging devotion to ships and sailing runs throughout and is echoed in the dedication of the craftsmen in New England who practice the forgotten art of shipbuilding -- no matter that the ships have died along with their era. The soundtrack, the interaction of historical and modern footage, and the restrained narration create an evocative context for this intriguing look at a particular page in nautical history. ~ Eleanor Mannikka, All Movie Guide
also:
http://movies2.nytimes.com/gst/movie...ml?v_id=156980
also-Gremlins 2-The New Batch (1990) has Lightfoot listed as a songwriter.
http://entertainment.msn.com/celebs/celeb.aspx?c=57194