A person stands fishing from morning into evening, and the poem gives us just three short lines to hold that whole stretch of time. The speaker fishes "till night," which suggests patience, or maybe a reluctance to leave. Nothing is said about catching anything. The waiting seems to be the point.
The strangest and most striking moment is the comparison to a scarecrow. Like a scarecrow, the angler stays in one spot, still and silent, part of the landscape more than a visitor in it. There's a gentle humor in the image, but also a hint of loneliness, since a scarecrow stands guard over a field with no one to talk to.
The last line, "my quiet oaths," is open to interpretation. It could mean muttered curses at a lost fish or a tangled line, or it could be something more like private vows. Either way, the speaker's feelings stay hushed and inward. The mood is calm, solitary, and slightly wry, a small portrait of someone content to be still while the light fades.