why isn't an estimate enough. If you catch many fish you should be able to make a fairly good guess when seeing a fish. I have never taped or weighed a fish that I am going to release. Maybe we should be more interested in getting the fish on his way. I personally would have no problem if it was illegal to take a fish out of the water that is going to be released. If you just have to take a measurement only take a length most times that will get you close enough and limit the stress on fish. Most times a 30" fish is 10 lbs a 31" fish 11 lbs and so forth on up
just my .02