They are different forms of the same verb, but in the world of fisheries science and in state law, they have very different meanings.

State law defines overfishing as “fishing that causes a level of mortality that prevents a fishery from producing a sustainable harvest” (NCGS § 113-129).

Overfished is “the condition of a fishery that occurs when the spawning stock biomass of the fishery is below the level that is adequate for the recruitment class of a fishery to replace the spawning class of the fishery.”

The definitions themselves use terms that need explanation to fully understand, so here’s a primer.

First, sustainable harvest — harvesting at a sustainable rate allows the population numbers to be maintained or even increase over time. The long-term yield (harvest) from a fish population partially depends on the rate of harvest (fishing mortality). If there is no or little harvest, then there will be no, or a small amount of yield from the fish population. If harvest is too high, the population will decline. In theory, there is a harvest rate, known as maximum sustainable yield that will maximize the long-term yield from the fishery. Fishing at a rate higher than that which produces the maximum sustainable yield is known as overfishing, and leads to a reduction in the long-term yield from the population. In this circumstance, reducing the harvest rate would lead to an increase in catches over time.

A fish population is said to be overfished when the spawning stock is below a level that cannot replenish itself through natural reproduction. The spawning stock, or mature part of the population, is that part of the population that is capable of producing offspring, also known as recruits. A certain number of recruits are needed to maintain, or sustain future populations. This number of recruits is specific to each species based on things such as life, history and the nature of the fisheries that harvest the population. If the population is fished so heavily that the spawning stock (mature fish) is reduced to the point that not enough young fish are produced to ensure the stock will maintain itself, the stock is considered overfished.