§ 285.26 - Size classes.  

Total curved fork length will be the sole criterion for determining the size class of whole (head on) Atlantic bluefin tuna. For this purpose, all measurements must be taken in a line tracing the contour of the body from the tip of the upper jaw to the fork of the tail, which abuts the ventral side of the pectoral fin and the ventral side of the caudal keel. For any Atlantic bluefin tuna found with the head removed, it is deemed, for purposes of this subpart, that the tuna, when caught, fell into a size class in accordance with the following formula: Total curved fork length equals pectoral fin curved fork length multiplied by a factor of 1.35. The pectoral fin curved fork length will be the sole criterion for determining the size class of a beheaded Atlantic bluefin tuna. For this purpose, all measurements must be taken in a line tracing the contour of the body from the ventral side of the pectoral fin to the fork of the tail, which abuts the ventral side of the caudal keel.