I agree with Dave. Fish will not grow much over winter. I don't think you would need to do any fish measurements until spring and then again in autumn.
If you think about it in spring of 2006 make a note of when the surface water temp of the GG pond gets to 55 or 60F. At that point you might want record the length of a few GG. Decent growth should start about that time.
Then try and note when the water temp again falls to 55 or 60F in the fall and measure a few more GG. This will allow us to calculate how many growing days there were for increase in body length.
