Step 3: Identify hammerhead 1st dorsal fins.Is the fin "short" (O-A divided by W is less than 2.5)?
1) Measure fin origin to apex (O-A).
2) Measure the fin width (W) at the halfway point of O-A (i.e., if O-A is 10 cm, measure W at 5 cm along O-A).
3) Divide O-A by W (O-A/W).
Origin, apex and fin width (measured from leading edge to trailing edge) are landmarks found to be the most useful for species identification purposes, as measurements based on fin height, fin base and free rear tip were often too variable and dependent on cut and condition of the fin.
Fin is "short"(O-A divided by W is less than 2.5)
Fin is "tall" (O-A divided by W is greater than 2.5)