What does atlantic cod eat?

Almost everything unusual about how a cod feeds follows from cold water. Feeding activity rises as temperature falls across most of the range, which is the reverse of nearly every other fish an angler meets, and it is why the North Atlantic cod fisheries are winter fisheries rather than a summer inconvenience.

The animal is built for finding food it cannot see. The chin barbel is a chemosensory organ, the lateral line reads movement close to the bottom, and vision does the last metre. A cod working rough ground at night in coloured water is not handicapped in the way a visual hunter would be.

Diet composition shifts twice over a lifetime. Small cod take crustaceans, worms and small molluscs; as gape allows, fish become the dominant item, and large cod are substantially piscivorous. The catalogue holds three verified prey relationships and all three are shoaling forage fish — sandeel, capelin and herring — which is the diet of an adult rather than of the whole species.

The geography of that is worth stating. Sandeel dominates in the North Sea, capelin in the Barents Sea and off Iceland and Greenland, herring wherever a herring stock persists. Cod condition in a given year tracks the abundance of whichever of those is local, and the collapse of a forage stock shows up in cod growth before it shows up anywhere else.

Anglers read the temperature relationship as the single most useful fact about the species, and it is the one piece of the biology above that transfers directly into a decision: cold water means feeding cod, and the season runs the opposite way to most sea fishing.

The scent-led sensory profile is used to argue for oily, strongly scented baits fished hard on the bottom, and for the observation that a cod will find a bait in conditions where a visual predator would not. That reasoning is widely and independently held across the northern European sea angling tradition and is convention rather than a tested result.

The shift towards fish prey with size is used to argue for larger baits where large cod are the target. It is a plausible inference from gape and from the recorded diet, and it is not evidence that a large bait selects for large fish — smaller cod take large baits routinely.

Three verified prey relationships describe an adult cod in the northern part of the range and understate both the invertebrate component and the regional variation. Diet composition differs between the North Sea, the Barents Sea, Icelandic waters and the western Atlantic, and between seasons in all of them. Nothing here establishes what any cod is eating in any particular week, and the temperature relationship describes a tendency across a stock rather than a rule about an individual fish.