The girl looked down into her left hand and began to whistle softly to herself. There was a happy note of triumph in the whistle. She was whistling 'Marion', a plaintive little calypso that has now been cleaned up and made famous outside Jamaica. It had always been one of Bond's favourites. It went:
All day, all night, Marion,
Sittin' by the seaside siftin' sand…
The girl broke off to stretch her arms out in a deep yawn. Bond smiled to himself. He wetted his lips and took up the refrain:
“The water from her eyes could sail a boat, The hair on her head could tie a goat…”
James Bond has just awoken on Crab Key and has seen what he compares mentally to Botticelli's Venus, he watches a few more moments, as she picks up shells, she begins to whistle a tune that Bond recognizes.
The tune referenced by Ian Fleming here is actually entitled Mary-Ann (or Marianne). Composed by Roaring Lion (Rafael de Leon) in 1941, the song was not released until 1945. (Interview with Roaring Lion.)
As Fleming/Bond note the song did become famous outside of Jamaica, as versions from Terry Gilkyson and The Easy Riders, Burl Ives, The Hilltoppers, The Brothers Four, The Merrymen, and Harry Belafonte were released during the late 1950's and 60's.
Here is the version from Roaring Lion himself: