WetRuler in action at New Sagaya
As fish grow in length, they increase in weight. The relationship between weight and length is not linear. The relationship between length (L) and weight (W) can be expressed as:
W = aL^b
When the equation is for standard weight, the standard weight for a given length is written as Ws. The exponent b is close to 3.0 for most species. The coefficient a varies between species. If the exponent bis greater than three for a certain fish species, that species tends to become relatively fatter or have more girth as it grows longer. For largemouth bass, the value of b is 3.273. If the exponent b is less than three for a certain fish species, that species tends to be more streamlined. For burbot, the value of b is 2.898. While the standard weight for a largemouth bass that is 500 mm long is about 2 kg, the standard weight for a burbot that is 500 mm long is only about 0.9 kg.
Standard weight in fish--Wikipedia
Weight-Length Algorithms The square-cube law is a mathematical principle, applied in a variety of scientific fields, which describes the relationship between the volume and the surface area as a shape’s size increases or decreases. It was first described in 1638 by Galileo in his Two New Sciences as the “ …ratio of two volumes is greater than the ratio of their surfaces.”
The values for a and b used in the look up table in WetRuler all come from the same source:
Their listings of values from a extensive variety of studies for a very large group of fish are all standardized to cm/gm measurements enabling easy adoption. Other apps with their own regional fish populations can easily be populated from this database and we anticipate building these in the near future. The code will be open source and available on GitHub.
Weight = A(Length)**B
The relationship between weight and length is assumed to follow an allometric growth equation
Log (W) = Log(A) +B *Log(L)
Graphing this gives access to data for various fish species for A and B
Certainly Not--its a free app with a dubious parentage based on a mixed variety of studies--some of which documented that it is very hard to get accurate results when weighing a moving fish on a old spring scale.
The WetRuler works using Apples newest Augmented Reality ARKit. It forms a 3D representation of the surround by memorizing multiple spots of familiar space. It then finds any flat planes within this realm and draws a grid knowing how far away all the spots on the grid are located. By locating a fish on the grid you tap the end of the tail and tip of the nose and the app figures the length accurately and then uses the particular log formulas for the weight.
We see potential uses for this app among sports fisherman with catch and release limitations enabling in water weight checks. Database studies for Fish and Game may find the app useful when large number of fish need to be evaluated. Since the software will be open sourced local changes in the log constants can be done for specific populations. It could play a future role in the need for careful documentation of fish catch limits.