Thanks for the links Norman. That's what I was starting to think as well, with the searching I've been doing. I've played around with pre-focusing, having the shutter button half way depressed, and so on, but these have only helped a little bit, and only some of the time.

This does seem to confirm for me that a full digital camera (not a digital SLR) is not a very good tool for one handed action shots of fish when there's nobody else around to hold the fish steady.