The following six metrics are the most commonly used for measuring the length of tunas, billfish, other bony fish, sharks, rays, and turtles. Ideally, the observer has a set of calipers and a slate, waterproof paper, or other writing options for wet work.
Fork Length (“FL”)
- Measurement: The length from the snout to the fork in the tail.
- Uses: For all tunas and other fish with a fork in the tail (including sharks).
Lower Jaw to Fork (“LF”)
- Measurement: The length from the lower jaw to the fork in the tail.
- Uses: For billfish.
Total Length (“TL”)
- Measurement: The total length of the fish.
- Uses: For all species with no fork in the tail.
Total Width (“TW”)
- Measurement: Total width of fish.
- Uses: For rays.
Carapace Length (“CL”)
- Measurement: Length of animal’s carapace.
- Uses: For turtles.