A Highland fishery board discovered the remains of the huge fish last week, which still had some teeth attached, in the River Conon.
According to the Cromarty Firth Fishery Board and Trust it is estimated the salmon was around 44lbs (20kg) during it’s prime.
Measuring 200mm from the tip of the jaw – known as the kype – to the hinge, the board compared the animal to a previous fish caught on a river in Norway.
The Cromarty Firth Fishery Board and Trust shared an image of the huge jawbone on their social media page over the weekend.
Dr Ross Glover, fisheries manager for the board, said: “It is a lower jaw from a male salmon (called a cock).
“We can tell this from the kype which is the hooked part at the end of the jaw.
“The jaw was found on the bank of the River Conon last week. I believe the jaw is from a salmon that would have spawned in the river in 2019.
“Most male salmon die after spawning and the condition of the jaw suggests it is not from the previous spawning season (autumn 2020).”
He added: “The jaw was compared to a wooden carving of a 44lb (20kg) salmon that was caught on the River Aaro (or Årøy) in Norway in 1923, and the dimensions are almost identical.
“Because of this, we believe the salmon would have been close to 40lb.
“This is not unusual for the River Conon as it has produced large, 30lb+ salmon in recent years.
“In 2019, the Malloch Trophy (for one of the largest fish caught by fly and released) was awarded to a 32lb salmon caught on the River Conon.”
Dr Glover explained that the jaw recovered was likely from a multi-sea-winter salmon, having spent three years at sea.
However, because there were no scales on the remains, it is difficult to accurately age the fish, he explained.
He added: “Catching a salmon of this size would be an angler’s dream and would easily be a fish of a life-time.
“The Cromarty Firth Fishery Board recommend that all salmon are released back into the river to continue on their journey to spawn, allowing future generations of salmon to thrive.”
In 2019, Ian Mitchell, winner of the Malloch Trophy – for one of the largest salmon caught by an angler on a fly and safely returned during the year in Scottish waters – caught a 32lb fish caught in the River Conon.
It is understood to be the heaviest caught in the Easter Ross river for 35 years.
The fish was measured – at 44 inches long with a girth of 22 inches – by gillie Max McKinstrie and was witnessed by both Mr McKinstrie and Andy Hindhaugh.