Why does determining the precise age of pelagic fish like the white marlin present inherent scientific challenges?

Answer

The structures used for aging are not always as clear or reliable

The scientific community faces hurdles because the structures used for aging billfish are often not as clear or reliable as those of bottom-dwelling fish, and extracting and interpreting otoliths can be technically demanding.

Why does determining the precise age of pelagic fish like the white marlin present inherent scientific challenges?
animalfishlifespanMarlin