10.5 is a pretty small boat. I'd say somewhere between 7 and 8 would be good. I started with 8ft on my 13 ft boat, and they were a little short. I'm at 9ft with the extenders.
Leverage/length for oars is also important because longer oars give you more thrust per stroke, but requires more energy because you are pushing them a farther distance. It is like gear ratio for a car or bike. Think "high" gear for longer oars. Shorter is easier to make faster/more strokes with less effort, like low gear for a bike or a car.
You shouldn't need different oars for fishing vs. whitewater. Or, for whitewater, you could ditch the frame, and run a small boat like that as an R2 creeker... Give me a shout if you are still in the Eagle area and want to go play.
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