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Spawning potential ratio

The amount of eggs produced by a fish stock over its lifespan under a specific fishing regime, relative to the spawn that would have been produced over the fish stock’s lifespan if there were no fishing. It is a measure of the impact that fishing has on the ability of a fish stock to contribute to spawning. Often expressed as a percentage. For example, SPR_50% means that under the specified fishing mortality rate, a recruit will, on average, produce half the eggs in its lifetime that it would have produced without fishing.

Maximum sustainable yield

The largest long-term average yield that can be taken from a stock under existing environmental conditions and a constant fishing mortality rate.

Fishing mortality at the maximum sustainable yield

The level of fishing intensity that, if applied constantly year after year, would result in B_MSY and the maximum sustainable yield (MSY) on average over the long term.

Yield per recruit

The expected lifetime yield per fish recruited in the stock at a specific age. YPR depends on the exploitation pattern (fishing mortality at age, F) and natural mortality (M).

Catch in weight or Yield

Total weight of fish harvested from a fishery. Yield does not necessarily correspond to landed weight. The difference between the two values, yield, and landings, is mainly due to discards at sea of part of the catch which, for some reason (price, quality, storage limitations or even legal reasons), is not landed.

Spawning stock biomass capable of producing maximum sustainable yield

This is the stock size (biomass) of spawners that would result on average if FMSY was applied constantly year after year. SSBMSY is often measured by the biomass of female spawners.

See also SB.

Stock‑Recruitment relationship

The relationship between the parental fish stock (spawning biomass) and the resulting recruitment (usually the number of recruits to the exploitable phase). The SRR is used to predict the average number of recruits that would be produced at different population sizes.

Recruitment

The amount of new fish added to the exploitable stock each year—due to population growth and/or migration into the fishing area.

Maximum economic yield

The value of the largest positive difference between total fishing revenues and total costs of fishing (including the cost of labor, capital, management, and research).

Natural mortality rate

Deaths of fish from all causes except fishing (e.g., from disease, predation, and starvation). Usually expressed as an instantaneous rate or as a percentage of fish dying in a year.

See also F.