John,
You're right, and the approach you take on small rivers is mine also. The expectation is to usually catch one or two fish from the better swims (if i'm lucky!) before moving on. Smaller groups of fish, the knowledge that some disturbance will put any remaining fish on their guard means moving on is probably the best option - with a return later on.
Judging the number and size of the chub in any given swim is the key. This isn’t such a problem on the small rivers I fish because the bigger fish are very few and far between and usually occupy swims with no more than half a dozen chub in them. That scenario is perfect for the big-bait / roving approach - optimising the dusk period, rotation priming of swims with mashed bread or a few hook samples etc. This is classic chub fishing that many of us practice, and I’ll never tire of.
It’s when you have a bigger shoal of chub in front of you, and consisting of much larger individual specimens that the feeding is key. This scenario is one I, and friends have met with numerous times on bigger rivers like the Dorset Stour and Thames, and in the past I would fish them in exactly the same way as I’ve described for the smaller rivers. And you get very similar results - one or two fish here and there, move on, and so on. In fact, most of my biggest fish have come from the first cast made into a new swim -a cautious approach with a big, single hook bait maybe catching these extra wary fish unawares, I don’t know? The potential for these swims is, however, far greater. I don’t really enjoy feeder fishing, can do it but it’s just a personal thing, and while I know it is a devastating method I much prefer to exploit the main weakness in the chub’s natural defence armoury - the fact that they just cannot resist a bait falling naturally through the water. And float fishing, summer or winter can be devastating. This whole subject would merit a whole response on its own, but what I would say Paul, those fish you saw swirling earlier in the day were probably eating everything in sight, and were probably very catchable even in the brightest, clearest of water conditions.
Matt