Introduction to stock assessment
Unit 1.2: What is stock assessment?
Stock-recruitment relationships are often important to stock assessments. They are the relationships between the abundance or biomass of spawning adults in a stock and the expected number of recruits they can produce each year. In other words, the number of young fish in a stock depends on the number of mature fish that can reproduce each year. Where possible, these relationships can help determine the extent to which a fish stock can be harvested (or, how many fish are available to catch and how many should be left in the water to reproduce).
Information that can help determine a stock's stock-recruitment relationship includes:
Steepness or recruitment compensation
Steepness or recruitment compensation is a measure of juvenile fish survival when there is little or no competition for resources (for example, food or habitat).
Spawning potential ratio
Spawning potential ratio is the number of eggs produced by a fish stock being fished relative to number of eggs that would be produced if it is not fished.
Yield per recruit
Yield per recruit is the expected lifetime catch in weight produced per recruited fish in the stock.
Unfished biomass
Unfished biomass is the total weight of fish that would exist in a stock if it is not fished.
Unfished recruitment
Unfished recruitment is the expected recruitment if the fish stock is not fished.
Depletion
Depletion is a measure of the current biomass of a stock relative to the average unfished biomass.
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