Rich,
Runs are maybe not as defined as they once were but most rivers still get a peak period and it usually occurs at about the same time each season given like conditions. When looking at catch data, it is useful to have some information about conditions to hand. As noted by Hamish above, some systems (or parts of) do not get any fish at points in the season. Let me know when you are coming over in good time and I'll get something sorted out.
Cheers
Ben