Converting Fish Lengths |
Example of conversions based on morphometric data:
In this example, we will use humpback chub, Gila cypha. These conversion factors are only valid for fish that have achieved their adult body form; very young fish have different body morphologies. Notice that the conversion factors are dimensionless so you can use any units of measure (Examples: feet, inches, centimeters).
Excerpt from the Morphometric Data Table:
Common name |
Family |
Genus |
Species |
BD/TL |
TL/SL |
TL/FL |
broad whitefish |
Salmonidae |
Coregonus |
nasus |
0.232 |
1.165 |
1.099 |
humpback chub |
Cyprinidae |
Gila |
cypha |
0.224 |
1.252 |
1.134 |
humpback whitefish |
Salmonidae |
Coregonus |
pidschian |
0.196 |
1.142 |
1.078 |
inconnu |
Salmonidae |
Stenodus |
leucichthys |
0.174 |
1.146 |
1.080 |
lake sturgeon |
Acipenseridae |
Acipenser |
fulvescens |
0.118 |
1.186 |
1.096 |
Where: BD = Body Depth, TL = Total Length, SL = Standard Length, FL = Fork Length
1. There are three possibilities:
a. If you need body depth and you have total length, then use the column BD/TL (body depth/total length) and the row - humpback chub = 0.224.
b. If you have fork length and you need total length, then use the column TL/FL (total length/fork length) and the humbback chub row = 1.134.
c. If you have standard length and you need total length, then use the column SL/TL (total length/standard length) and the humpback chub row = 1.252.
2. Multiply the length you have by the conversion factor as follows.
a. For a humpback chub with a total length of 8.5 inches to estimate body depth:
BD/TL x TL = BD
0.224 x 8.5 inches = 1.9 inches body depth
b. For a humpback chub with a fork length of 21.6 centimeters to estimate total length:
TL/FL x FL = TL
1.134 x 21.6 cm = 24.5 cm total length
c. For a humpback chum with a standard length of 203 millimeters:
SL/FL x SL = TL
1.252 x 203 mm = 254.2 mm total length