Per the question in the title of this post, the folks at Norre certainly think so. That's why they developed the Tail Scale, which is demonstrated in the Kickstarter video below. There is no doubt that you can tell a big fish just by looking at the tail, but this is the first time I've ever heard anyone claim you can get a pretty tight estimate of length and weight just by measuring the tail. The first Tail Scale is just for trout, and the real purpose of the gadget is to help you get solid measurements with minimal fish handling. So what do you think? Would you trust the Tail Scale to nail the measurement as well as a tape? If you want more details about the science behind the tail measurement system, check out Norre's Kickstarter page.