Good for mapping but probably little use distinguishing large fish from medium and small sizes of fish. In fish sizes department it is not that sensitive separating medium sized vs lg fish. It would have to be calibrated and noted what size makes the symbol move up to the next larger size. Plus fish are continually moving around and getting any quantitative answer would be very difficult.

aka Pond Doctor & Dr. Perca Read Pond Boss Magazine -
America's Journal of Pond Management