Just to clarify, under the Fisheries Act, RCMP officers are designated Fishery Officers. As such they are able to enforce the Fisheries Act.
The Act clearly states in Section 33. No person shall purchase, sell or possess any fish that has been caught in contravention of this Act or the regulations.
Seeing as DFO put out a notice on August 28 that all retention of sockeye was closed, including for the Natives, the two guys in the boat were clearly in violating the Fisheries Act.
As for throwing the fish into the water, that was the only way from preventing them to continue the offence. If they keep the fish, then they continue to break the law. Had DFO been there and intervened, they would have thrown the fish in the water after taking photographs etc.
Seems to me we can safely assume that this cop knew what he was doing....