Atlantic cod: life, behaviour and the long reads

Cod present two handling problems and neither is the fish being dangerous. There are no meaningful spines, no teeth worth avoiding and no sharp covers.

The first problem is the mouth. A cod's jaw tissue is soft and tears easily, so a fish lifted by the lower jaw — the grip anglers default to on large fish — can be damaged before it is even unhooked. Support the body, use a net for anything substantial, and lift with two hands rather than by the head.

The second is depth, and it is the one that decides survival. Cod taken from any real depth suffer swim bladder expansion they cannot equalise, and a fish that arrives with its stomach protruding from its mouth and bulging eyes is not recoverable by being put back gently. It floats and it dies.

Where release is intended from depth, a descending device returns the fish to a depth at which the gas recompresses. Venting is the older approach and is easier to do badly. Where neither is available, the honest position is that the fish is unlikely to survive release and the decision about whether to fish that depth is the one that mattered.

Cod are a demersal predator of cold water, and the shore fishery for them exists because of a specific relationship between the fish, the ground and the sea state.

THEY ARE BOTTOM-ORIENTED BUT NOT BOTTOM-FIXED. Cod feed on and near the seabed, taking crustaceans, molluscs, worms and fish, and they move over ground rather than holding a fixed station. Their mouth and feeding style suit hard broken ground with a lot of prey in it — rock, boulder, mussel bed, kelp stump, wreck and the mixed ground where sand meets rock.

WHICH IS WHY SHORE COD FISHING IS ROUGH-GROUND FISHING. The ground that holds the food is the ground that costs terminal tackle, and the whole design of shore cod fishing — rotten-bottom links, pulley rigs, heavy line — exists to fish ground that would otherwise be unfishable. An angler avoiding tackle losses is usually avoiding the fish.

THE DEPTH RANGE IS ENORMOUS and the inshore fish are a shallow fringe of a distribution running to hundreds of metres. That matters practically because the boat fishery and the shore fishery are working different parts of the same population, and the size structure differs accordingly.

COLOURED, DISTURBED WATER IS PART OF THE HABITAT RATHER THAN AN OBSTACLE TO IT. A sea that has been stirred by weather dislodges food from the ground and reduces visibility, and cod feed confidently in it in a way they do not in clear calm water. The relationship between rough weather and inshore cod fishing is well established among practitioners and is consistent with what the fish eats and how it finds it.

AND THE STOCK IS THE UNIT THAT MATTERS. Cod occur across the North Atlantic in stocks whose status differs enormously, and the sensible question about cod anywhere is not about the species but about the stock in that area. Advice is issued per stock for that reason.

In the southern part of the European range, shore cod fishing is a cold-weather pursuit almost by definition, and the reason is thermal rather than traditional.

COD ARE A COLD-WATER SPECIES near their southern limit in the southern North Sea, the Channel and the Irish Sea. As inshore water warms through summer, they retreat to deeper, cooler water. As it cools through autumn and winter, they move back within reach of the shore. The season is therefore set by the temperature the water reaches rather than by a month, and it starts later after a warm autumn.

FURTHER NORTH THE PATTERN FLATTENS. Where inshore water stays cold enough year-round, cod are available inshore for much more of the year, and the winter-only framing simply does not apply. The mechanism is the same; the outcome differs entirely with latitude.

SPAWNING SHAPES LATE WINTER. Cod spawn in winter and early spring in specific traditional areas, and adults move to those grounds. Fish are in poorer condition after spawning and improve through the feeding period that follows.

WEATHER MATTERS MORE THAN SEASON WITHIN THE SEASON. A gale that colours the water and dislodges food onto the ground frequently produces the best inshore fishing of the year, and the two or three days after a big sea are widely regarded as the most productive. This is practitioner consensus supported by a plausible mechanism rather than a measured effect, and it is worth labelling as such.

AND THE LONGER TREND IS PART OF THE ANSWER. The southern limit of cod has been shifting, distribution has changed markedly over recent decades, and inshore cod fishing in parts of the southern range is not what it was within living memory. That is a stock and climate question rather than a seasonal one, and it means historical accounts of a local cod season may describe a fishery that no longer behaves that way.

Cod reproduction is the most consequential piece of fish biology in the North Atlantic, because the way the species spawns is exactly what made it vulnerable to the fisheries that depleted it.

THE STRATEGY IS MASS BROADCAST. Cod spawn in winter and early spring, releasing very large numbers of pelagic eggs into the water column. A large female produces eggs in numbers that are hard to picture. The eggs drift, the larvae drift, and the survivors settle to the bottom as juveniles wherever the currents have taken them.

AND THE AGGREGATIONS ARE FAITHFUL TO PARTICULAR GROUND. Cod return to specific, traditional spawning areas, and they do so predictably in time and place. That fidelity is the important fact: it made the spawning shoals findable by fisheries year after year, at the moment the fish were most concentrated and least evasive, and it is a large part of the story of how several stocks were reduced so far and why some have not recovered.

LARGE FEMALES ARE NOT INTERCHANGEABLE WITH SMALL ONES. Egg production rises steeply with size, and larger older females spawn over a longer period and produce larvae with better survival. A stock whose age structure has been truncated by fishing has lost more reproductive capacity than its total weight suggests, which is why the historical fish of twenty-five kilograms are a management observation rather than a curiosity.

RECOVERY IS SLOW AND NOT GUARANTEED. Several depleted cod stocks have failed to rebuild even after severe restriction, and the reasons — changed ecosystems, altered temperature, loss of the older age classes — are still argued about. FishingHQ records that as unresolved because it is.

WHAT THIS SECTION DOES NOT DO. It does not identify spawning grounds or times for the purpose of fishing them. The predictability of a spawning aggregation is the reason for restrictions, not an opportunity.

Cod size is the clearest case on FishingHQ of maximum figures describing a different world rather than an achievable one.

THE ORDINARY FISH. Most rod-caught cod in accessible European water are between forty and seventy centimetres and one to four kilograms. That is what a good day produces and it is what the shore fishery is built around.

A GOOD FISH is over ninety centimetres and around nine kilograms. In most inshore fisheries in the southern range that is a notable capture rather than a routine one.

THE EXCEPTIONAL FIGURES ARE HISTORICAL. Fish well over twenty-five kilograms are recorded. They are not a target and in most areas they are not a realistic possibility, because a fish of that size requires an age structure that heavy exploitation has removed from most stocks. The maximum is real; the population that produced it largely is not.

WHICH MAKES THE NUMBER INFORMATIVE RATHER THAN ASPIRATIONAL. The gap between what cod can reach and what they now typically reach is a direct measurement of what happened to the stocks, and it is more useful read that way than as a record to chase.

GROWTH VARIES WITH STOCK AND TEMPERATURE. Cod in different parts of the range grow at very different rates and mature at different sizes, so a length-for-age figure from one area does not transfer. Where a minimum size applies it is set for a stock and an area, and it changes.

AND THE PRACTICAL CONSEQUENCE FOR AN ANGLER. A large cod is old, and in a stock under pressure it is disproportionately valuable in the water. That is an argument for returning big fish that rests on demography rather than on sentiment.

Cod tackle is a good illustration of a general principle in sea angling: the fish is rarely the design constraint, and understanding what actually is makes tackle choices obvious.

DEPTH AND TIDE SET THE LEAD, AND THE LEAD SETS EVERYTHING ELSE. Fishing on the bottom in forty metres with a tide running requires enough weight to hold, and how much weight depends almost entirely on the diameter of the line being dragged through the water rather than on the fish. Thinner line means less water resistance means less lead means better bite detection and less effort. That single chain of consequences explains why braided line changed deep-water cod fishing so completely.

THE GROUND DECIDES THE STRENGTH. Over clean sand or mud, a cod can be played on light tackle without difficulty. Over a wreck or hard reef, the fish must be lifted clear of structure immediately or it will not be landed, and that requires a rod with lifting power and line that will survive contact. Wreck tackle is heavy because of the wreck.

COD FIGHT BY WEIGHT AND DEPTH, NOT BY SPEED. A cod is a heavy, deep-bodied fish that resists steadily and uses the current rather than running, so what tackle needs is lifting capacity and a reel with the retrieve to recover line, not a drag capable of surviving a long fast run.

SHORE FISHING IS A DIFFERENT PROBLEM AGAIN and it is mostly about casting a bait to where the fish are in a sea that is moving. Distance, holding capability and the ability to present a large bait dominate the choice, and the fish that arrives is frequently smaller than the tackle suggests.

BAROTRAUMA MAKES TACKLE A WELFARE VARIABLE IN DEEP WATER. A cod brought quickly from depth suffers swim bladder expansion, and a fish that is to be returned has better prospects if it is brought up steadily and released promptly. Tackle heavy enough to shorten the fight is, in that context, the kinder option — the reverse of the usual assumption.

AND HOOK SIZE FOLLOWS THE BAIT RATHER THAN THE FISH. Cod take large baits and a hook must be large enough to leave the point clear, which is why cod hooks look oversized next to the mouths they end up in.

Cod are among the least selective feeders a sea angler pursues, which shifts the bait question from what they will eat to what will still be there when they arrive.

THE FISH TAKES ALMOST ANYTHING OF ANIMAL ORIGIN. A cod's gut contents routinely include fish, crabs, molluscs, worms, squid, starfish and things no fish should reasonably eat. So bait selection is not about persuading a cod to accept an item; it is about presenting a large, strongly scented item at the right depth and having it survive long enough.

SIZE IS DELIBERATE AND IT IS A SELECTION TOOL. A large bait deters small fish and crabs from stripping it and, in practice, selects for larger cod. That is why cod baits look excessive — big worm baits, whole squid, large fish sections, or several baits combined into a cocktail on one hook. A small neat bait in a cod mark is eaten by everything else first.

SCENT AND OIL DO THE WORK IN DEEP OR COLOURED WATER. Cod hunt substantially by smell, particularly at depth and at night, and baits that leak oil and amino acids into the tide draw fish from further away. Fresh oily fish, squid and worm all do this; a washed-out bait does not, which is why baits are refreshed rather than left down indefinitely.

DURABILITY IS THE OTHER HALF AND IT SETS THE PRACTICAL CHOICE. In a strong tide, in the presence of crabs, or when casting hard from a beach, a bait must stay on the hook. Squid, and baits bound with bait elastic, survive; a soft worm bait cast at distance does not without help. Combining a soft attractive bait with a durable one is the standard resolution.

SHELLFISH BAITS AFTER A BLOW ARE A REAL AND SPECIFIC PATTERN. A storm that breaks razor clams, mussels and other shellfish out of the ground produces a period in which cod are actively feeding on them along a coast, and matching that is one of the clearest bait-matching situations in shore fishing.

AND WHERE BAIT IS DUG OR GATHERED, PERMISSION AND RESTRICTION APPLY. Worm digging and shellfish collection are regulated in many areas by area, season, quantity or permit, and the arrangements differ. The competent authority is the source.

Cod are fished for in three distinct ways, and the differences between them are larger than the similarities — which is why advice from one is so often useless in another.

SHORE FISHING IS A BAIT-AND-DISTANCE DISCIPLINE conducted mostly at night, mostly in the colder months, and mostly in unsettled water. The essentials are a large scented bait, enough lead to hold in the surf and tide, and the ability to reach the ground where fish are working. Coloured water after a blow is the classic condition because it brings cod close in and puts food in suspension. The method is patient and static; the skill is in bait, timing and reading the beach.

BOAT FISHING OVER OPEN GROUND is bottom fishing with bait at anchor or on the drift, and its main variable is tide. Enough lead to hold, a trace that presents the bait naturally, and the discipline to refresh bait rather than leave it down. This is the most forgiving of the three and the best introduction to the species.

WRECK AND ROUGH-GROUND FISHING IS A DIFFERENT PROPOSITION ENTIRELY. Cod hold on and around structure, and both bait and lure methods are used — pirks, large jigs and soft plastics worked over the wreck, or baits fished on the ground. The difficulty is tackle loss and the requirement to move a hooked fish away from structure at once, and the tackle section explains the consequences for gear.

JIGGING AND LURE FISHING HAS GROWN CONSIDERABLY and it is genuinely effective — a large soft plastic or a metal worked near the bottom takes cod well and is more mobile than bait fishing. It also avoids the bait-supply problem entirely.

DEPTH GOVERNS WHETHER RELEASE IS POSSIBLE, as with every deep-water species. A cod from substantial depth suffers barotrauma and its prospects on release are poor without recompression; a cod from the shore or shallow ground is generally returnable. That is worth deciding before fishing rather than at the rail.

AND COD ARE SUBJECT TO MANAGEMENT MEASURES THAT DIFFER BY AREA AND CHANGE, sometimes substantially. What may be retained, in what quantity and when is a matter for the competent authority and nothing here indicates it.

Cod are highly fecund — a large female produces millions of eggs — and grow quickly where feeding allows. They mature at two to six years depending on stock and temperature, and can live well over twenty years, though few now do in heavily fished areas. Because fecundity rises steeply with size, the removal of large old females has a disproportionate effect on a stock's ability to recover, which is one of the central lessons of the species' management history.

Cod spawn in winter and early spring in specific, traditional spawning areas, releasing enormous numbers of pelagic eggs into the water column. Larvae drift with currents before settling to the bottom as juveniles. The fidelity of spawning aggregations to particular grounds made them both predictable to fisheries and vulnerable to them.

Cod are opportunistic bottom-oriented predators taking crustaceans, molluscs, worms, squid and fish, with diet shifting towards fish as they grow. They hunt largely by sight and smell close to the bottom and around structure, and are notably associated with reefs, wrecks and rough ground where prey concentrates. Feeding activity increases in cold water, which is the reverse of most species an angler encounters and is why cod are a winter fish.

Smell and taste are important — the chin barbel is a chemosensory organ used to locate food on the bottom — and cod will find a scented bait in complete darkness and heavy coloured water. Vision matters at close range. The lateral line detects prey movement near the bottom.

In the southern part of the European range cod move inshore as water cools through autumn and winter and retreat as it warms, which makes shore cod fishing a cold, dark, rough-weather pursuit almost by definition. Further north they are available inshore for more of the year. Rough seas that colour the water and dislodge food frequently improve shore fishing markedly.

A principal winter target for shore and boat sea anglers across northern Europe, and the species that most shapes heavy shore tackle design. Also the species where recreational anglers most directly encounter the reality of fisheries management, since retention rules vary substantially by area and change.