Why has it always got to be some external influence that turns the bite off? I fish all the time where there is no boat influence and the bite practically never lasts all day. Just last week on the river where I fish all the time, I fished from just light until 4 p.m. I had scattered bites until around 8 a.m., the the fish bit like crazy until 10 a.m., then they stopped cold. Changed what I was using two or three times - drifted, spooned, used spinners, covered the entire flats, but couldn't coax a bite. Then, about 2 p.m., it turned on again. No boats, no rocking the hole, just whatever light and temperature changes went on without me being able to discern. This happens often. The bite goes on, then the bite turns off. Why wouldn't this continue to hold true to a large extent if boats and other influences were present. I think whatever is going on in the water has more to do with it than what is going on on or around the water.
I see this happen again and again whether I'm the only person on the bank or one of several on the bank fishing the same water. If some external disturbance happened to coincide with the bite turning off, it would be easy to blame, but it happens all the time, even under ideal conditions.
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Tad