The ideal fish for human consumption would mature quickly and reproduce in staggering numbers. This does not describe the Atlantic cod. Cod mature late — at 4 to 6 years old — and they can live as long as 25 years. Female cod do, in fact, produce astonishing numbers of eggs. But older cod lay two or three times as many eggs as younger cod. This means that a healthy cod population must include relatively large numbers of older fish.

A recent survey of cod catches in Northern Europe shows exactly the opposite. Extrapolating from survey numbers, scientists at a British government fisheries agency estimate that there are nearly 200 million 1-year-old cod in the North Sea but only 18 million 3-year-olds. As for older cod, the numbers are shocking. The survey team estimates that in 2011 there were only 600 12- to 13-year-old cod, a third of which were caught, and not a single fish older than 13 has been caught in the past year.

Most of the cod being caught are sexually immature, and the rest are just entering maturity. As for the great flood of eggs from older fish — as many as nine million in a single spawning — they have vanished. In other words, we have fished our way down the population until we’ve reached the boundary of reproduction.

That cod are in trouble will come as old news to New England, where the cod population essentially crashed years ago. Despite conservation efforts, and periodic reports of a comeback, New England cod populations are thought to be far below the number required for a sustainable fishery. Earlier this month, the Commerce Department issued a formal disaster declaration for the entire Northeastern commercial groundfish fishery, which includes cod.