California Code, Fish and Game Code - FGC § 8226

(a) Notwithstanding any measurement requirements under this code, and to implement the department's salmon tagging program, any person in possession of a salmon with a missing adipose fin, the small, fleshy fin on the back of the fish between the back fin and the tail, upon request by an authorized agent or employee of the department, shall immediately relinquish the head of the salmon to the state, at no charge, for recovery of any coded-wire tag. The head may be removed by the fish owner or, if removed by the official department representative, the head shall be removed in a manner to minimize loss of salmon flesh and the salmon shall immediately be returned to the rightful owner.

(b) It is unlawful to intentionally conceal, cull, or release into the waters, a salmon with a missing adipose fin that it is otherwise legal to possess.