Cod

• 1. Introduction

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  Cod sits at the center of one of the most consequential stories in the history of human interaction with the sea. On the 2nd of July 1992, Canada's Federal Minister of Fisheries and Oceans, John Crosbie, stood before the country and announced a moratorium on the Northern Cod fishery off the coast of Newfoundland. The total cod biomass had collapsed to less than 1% of its normal value. A fish that had sustained economies and cultures for five centuries vanished, in ecological terms, almost overnight.

  What kind of creature commands that much history? How did a single fish species shape the settlement of continents, fuel trade wars, and ultimately become a casualty of the very commerce it created? And what does its story reveal about the way humans have always treated the ocean's abundance as limitless?

• 2. The Fish Itself

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  Gadus morhua, the Atlantic cod, was formally named by the Swedish naturalist Linnaeus in 1758, though humans had been catching and eating it for centuries before science gave it a Latin name. The Atlantic cod can grow to 200 cm and reach a maximum recorded weight of 96 kg, with an average weight in adult specimens typically ranging from 5 to 12 kg. Its Pacific cousin, Gadus macrocephalus, is smaller, topping out at 119 cm and 22.7 kg.

  The body plan of a true cod is distinctive. Three rounded dorsal fins sit along the back; two anal fins run below. The upper jaw extends over the lower, and a chin barbel hangs beneath, roughly equal in length to the eye diameter. A white lateral line runs from the gill slit all the way to the base of the tail. The back tends toward greenish or sandy brown, with mottling that lightens toward the belly.

  Atlantic cod shift colour with depth, cycling between gray-green and reddish brown phases. Individuals living among rocky inshore regions often show dark brown colouring. The fish favours rough ground and roams depths between 6 and 600 m, with 80 m as the typical average. Off the Grand Banks of Newfoundland and along Norwegian and New England coasts, cod congregate seasonally in shallower bands of 30 to 70 m.

  Spawning runs from January through April, peaking in March and April, at roughly 200 m depth in water temperatures between 4 and 6 degrees Celsius. The courtship that precedes it involves fin displays and a distinctive male grunt. A pair swims in circles while spawning, releasing planktonic eggs that hatch in eight to 23 days. Larvae reach 4 mm in length and spend about ten weeks drifting, growing to 2 cm and increasing body weight by 40-fold before sinking to the seabed. Cod reach reproductive maturity at around 50 cm, typically at 3 to 4 years of age.

• 3. A Thousand-Year Market

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  Around 800 AD, during the Viking period, Norwegian fishermen began travelling with dried cod, and a trade market developed in southern Europe that would endure for more than a thousand years. It survived the Black Death, survived wars, survived crises that toppled other industries. That durability is remarkable because cod fishing grounds sit far from population centres, which meant the trade depended on large-scale sea transport from the earliest days.

  The large cod fisheries along the Norwegian coast, particularly near the Lofoten islands, were developed almost entirely for export from the start. Salt transformed the industry further: dried and salted cod, known in Norwegian as klippfisk, could be shipped even greater distances. By the end of the 14th century, the Hanseatic League had absorbed control of the trade, with Bergen as the dominant port.

  The Portuguese began fishing cod in the 15th century, and clipfish became a fixture of Portuguese cuisine that persists today. The Basques moved even further, allegedly reaching the Canadian fishing banks before Columbus made his crossing. The North American east coast developed in part because of the sheer abundance of cod in its offshore waters. Many cities in the New England region grew up near cod fishing grounds.

  Massachusetts encoded its dependence on the fish in a peculiar way: the state's House of Representatives hung a carved wooden codfish in its chambers. The carving became known as the Sacred Cod of Massachusetts. When William Pitt the Elder rose in Parliament to criticise the Treaty of Paris, he called cod "British gold" and warned it was folly to restore Newfoundland fishing rights to France.

  In 1733, Britain imposed the Molasses Act to squeeze the trade between New England and the British Caribbean. The plan backfired. French traders proved eager to enter contraband arrangements with New Englanders, and the cod trade expanded rather than contracted. The colonial merchants who profited organised themselves into what was known as a "codfish aristocracy."

• 4. Predator, Parasite, Prey

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  Adult cod are active predators. Their diet spans sand eels, whiting, haddock, smaller cod, squid, crabs, lobsters, mussels, worms, mackerel, and molluscs. In the Baltic Sea, herring and sprat are the primary prey, and stomach-content studies there confirm cod as the apex predator in those waters. Sprat concentrate in particularly high densities in the Bornholm Basin in the southern Baltic, which functions as a key feeding ground.

  The relationship with sprat is not simply predatory from one direction. Sprat prey on cod eggs and larvae, which means that a dense sprat population can suppress cod recruitment even in waters where adult cod appear healthy. This feedback loop complicates management: protecting adult cod does not automatically protect the next generation.

  The cod worm, Lernaeocera branchialis, runs a life cycle of considerable complexity at cod's expense. It begins as a free-swimming, copepod-like larva that attaches to a flatfish or lumpsucker, using grasping hooks to hold on and a thin filament to extract blood. Nourished, the larvae mate. The fertilized female then seeks a cod or cod-like host, clinging to the gills while transforming into a plump, sinusoidal worm with a coiled mass of egg strings at the rear. The worm's front portion penetrates into the host until it reaches the rear bulb of the cod's heart, where it branches into the main artery like tree roots. It feeds on the cod's blood while safely hidden under the gill cover, eventually releasing a new generation of larvae back into the water.

• 5. The Collapse

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  John Crosbie delivered his moratorium speech on the 1st of July 1992, at a fishing village, and was heckled by disgruntled locals before the formal declaration came the following day. The announcement halted the Northern Cod fishery off Newfoundland, the same fishery that had sustained coastal communities for five centuries.

  The immediate human toll was staggering. Some 19,000 fishermen and cod processing plant workers in Newfoundland lost their jobs. Nearly 40,000 workers and harvesters across Newfoundland and Labrador applied for relief through the federal program known as TAGS, the Atlantic Groundfish Strategy. Abandoned fishing boats still line the Newfoundland coast.

  The moratorium was designed to last two years. Cod populations did not recover; they continued falling. The moratorium was extended indefinitely. Exceptions remained for food fisheries for personal consumption, and some 12,000 tons of Northwest cod were still being caught annually along the Newfoundland coast even after the closure.

  What collapsed was a biomass of four million tons, a population that had survived multiple marine extinction events across tens of millions of years. Researchers cite the collapse, achieved in no more than 20 years of intensive industrial fishing, as one of the clearest examples of the Tragedy of the Commons. The contributing factors identified include overfishing, government mismanagement, the disregard of scientific uncertainty, warming waters, and declining reproduction.

  The technologies that accelerated the collapse were not primitive. Trawling, in particular, proved ecologically devastating in the years immediately preceding the 1990s. Fishermen and government officials alike operated under the assumption that ocean stocks could not be depleted. As of 2021, the Northern Cod biomass has been recovering, but growth has stagnated since 2017. Some scientists argue that the population will not rebound unless Canada's Fisheries Department cuts its yearly quota to 5,000 tons.

• 6. Naming, Marketing, and Confusion

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  The word "cod" creates a taxonomy problem that is partly linguistic and partly commercial. Three species in the genus Gadus are legitimately called cod: Atlantic cod, Pacific cod, and Greenland cod. A fourth Gadus species, Alaska pollock, is not commonly called cod at all, though trade names like snow cod or bigeye cod exist for it.

  Beyond genus Gadus, dozens of other fish carry the word in their common names, from the morid cods in family Moridae, which runs to around 100 species, to the eel cods in Muraenolepididae, which has four, to the single-species Eucla cod family. The tadpole cod family was reclassified from one order to another. Usage of these names varies across regions and has shifted over time.

  The Southern Hemisphere adds further complications. Fish in the order Perciformes, entirely unrelated to Gadus, carry cod names that have become established in trade: Murray cod, Trout cod, Mary River cod, and others. The Antarctic cod and Patagonian toothfish, marketed as cod, belong to the notothen family.

  Shrinking Atlantic cod stocks drove part of this expansion. As wild catches fell, fishmongers and markets reached for culinary replacements and attached "cod" to species with similar flesh textures. The name followed the plate rather than the phylogeny. Haddock and whiting, members of the same family Gadidae as Atlantic cod, are sometimes sold as cod outright. Young Atlantic cod or haddock prepared in strips is called scrod. In the United Kingdom, Atlantic cod remains one of the primary fish in fish and chips, alongside haddock and plaice.