What salmon eat at each stage of life

SALMON EAT COMPLETELY DIFFERENT THINGS AT EACH STAGE, AND AT ONE STAGE THEY DO NOT EAT AT ALL.

THE ALEVIN, still in the gravel, absorbs its yolk sac and eats nothing external.

THE FRY AND PARR feed in the river on invertebrate drift: aquatic insect larvae and nymphs, emerging insects, terrestrial insects falling in, and small crustaceans. This is a small-food, high-frequency diet and it produces slow growth — a parr may spend one to several years in fresh water reaching a size a marine environment would produce in weeks.

THE POST-SMOLT AND ADULT AT SEA eat on a completely different scale: crustaceans, particularly amphipods and euphausiids in the early marine phase, and then increasingly fish — sandeel, capelin, herring, sprat and their equivalents. Growth in this phase is dramatic, and it is the entire reason for the migration. A fish that left the river at a few tens of grams returns weighing kilograms.

THE RETURNING ADULT IN FRESH WATER DOES NOT FEED IN ANY SUBSTANTIAL WAY. Its digestive system regresses, and it lives on the reserves built at sea for the whole of the upstream journey, the wait, and the spawning itself.

AND THAT LAST FACT IS THE CENTRAL STRANGENESS OF SALMON ANGLING. A salmon in a river will take a fly, a lure or a bait, and it is not feeding. What the take actually is remains genuinely unresolved: proposals include residual feeding reflex, aggression, territorial response, curiosity and irritation, and none of them is established. Practitioners have argued about it for two centuries and the honest position is that nobody knows.

WHAT THAT MEANS PRACTICALLY, and it is a great deal. Salmon fishing cannot be reasoned about by matching the hatch or by imitating prey, because the fish is not hunting. What experienced salmon anglers actually work with are water height, temperature, light, the fish's willingness to respond on a given day, and presentation — depth, speed and the angle of the swing. That is why salmon fishing feels so unlike trout fishing despite the tackle overlap, and why so much of its literature is about water rather than about flies.

AND IT HAS A WELFARE CONSEQUENCE. A returning fish has a fixed energy budget for the whole of its river life, and a long fight spends some of it. That is one reason for the shift towards rapid playing and careful release on salmon rivers, quite apart from any stock argument.