If an official fishery sampler requests your salmon’s head, then yes, you must give it to them. The adipose fin of hatchery salmon is removed and a coded wire tag is inserted in the fish’s head at the hatchery.
Recovery of coded-wire tag from salmon head: Any person in possession of a recreationally taken salmon with a missing adipose fin (the small, fleshy fin on the back of the fish between the back fin and tail) shall immediately relinquish the head of the salmon, upon request by an authorized agent or employee of the Department, to facilitate the recovery of any coded-wire tag per CCR T-14, §1.73.
You can find more information about salmon regulations on the CDFW’s Ocean Salmon Fishery Information web page or the tagging and recovery program on the CalFish Monitoring web page.