My Dad grew up on the famous Restigouche River, and as a child in the 1930’s, I can remember him coming home after a day ‘up river’ - and when he'd open up the trunk of his car with a flourish, there would be 5 or 6 beautiful 30 to 40lb. salmon gleaming in the sun!! I’ve read that the top 10% of anglers catch an amazing 90% of all fish, and I’m sure my father was among that top 10%!
Even so, I think he would have been intrigued if he had known about a fish’s circulation system, because it would have explained what must have taken years of experience to learn. As the simple diagram shows, a fish basically has a closed-loop circulation system with its heart pumping the blood in a single loop around the body. Starting with the gills that act as the fish’s lungs, the red lines in the picture show where the oxygen-carrying blood flows. The oxygen is needed to make the muscles work. The black lines show places where little or no oxygen is left in the blood. But the heart itself is a muscle, and if the fish is fighting hard to get free of the hook and all the oxygen is used up when the blood reaches the heart, the heart stops pumping and the fish goes belly up until it again has an adequate oxygen supply.
New regulations stipulate that barb-less hooks be used to make it easier to release a fish. That means that you have little chance of landing a salmon unless you always keep your line tight - but not so tight that it breaks! If a light ‘leader’ line that is less visible in the water is used [my father would have used a 6 to 8 lb. test line], a big salmon can easily break it. So you have to let the salmon run as many times as it can with just the right resistance to deprive its heart of oxygen temporarily so that you can reel it in part way. A big fish can sometimes take up to an hour to land.
And after all that, if you are trying to scoop up your fish with a net, it is easy to lose your catch. The first few times the fish is close, trying to scare it by brandishing the net in front of its nose should cause it to make desperate attempts to get away, using up the last bit of oxygen in its heart muscle. Then you can easily scoop it up safely when you see the white of its belly.
As fishermen say, 'tight lines.' Rie