Mr. William H. Wood, the pioneer of tarpon fishing, was the originator
of the formula for estimating the weight of tarpon when first taken
from the water:
(Girth^2 × length)/800 = weight
I was puzzled for a long time trying to discover the reason for the
divisor being 800. A friendly fellow fisherman, Mr. B. R. Kittredge,
eventually solved the question as follows:
“Consider in the first place that the shape of the fish is represented
by two wedges placed base to base. The area of the base of a wedge
multiplied by half its length gives its cubic volume. So the volume of
the two wedges would be the area of the base multiplied by the length
of one wedge. The volume of a fish in cubic inches would be the area of
his middle section multiplied by half his length.
If you square the circumference of any given square you obtain a square
that is 16 times the area of the given square. For example 10 × 10 has
an area of 100. It has a circumference of 40 which squared gives 1,600.
So that the square of the girth of a fish divided by 16 would give the
area of that section of the fish. Multiply the area of this section by
half his length and you will have the cubic volume of the fish.