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Setting an Annual Catch Limit

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Important Definitions

Overfishing: The annual rate of catch is too high.

Maximum Sustainable Yield: The largest, long-term average catch that can be taken under existing conditions.

Scientific Uncertainty: Scientific uncertainty refers to uncertainty in the information about a stock and its maximum sustainable yield reference points. Sources of scientific uncertainty could include: uncertainty in stock assessment results; uncertainty in the estimates of maximum fishing mortality threshold, maximum stock size threshold, the biomass of the stock, and overfishing limit; time lags in updating assessments; the degree of retrospective revision of assessment results; uncertainty in projections; uncertainties due to the choice of assessment model; longer-term uncertainties due to potential ecosystem and environmental effects; or other factors.

Management Uncertainty: Management uncertainty refers to uncertainty in the ability of managers to constrain catch so that the annual catch limit is not exceeded, and the uncertainty in quantifying the true catch amounts (i.e., estimation errors). The sources of management uncertainty could include: late catch reporting; misreporting; underreporting of catches; lack of sufficient in-season management, including in-season closure authority; or other factors.


Setting an ACL is the result of a multi-step process:

Step 1. Calculate the stock’s overfishing limit, which is a catch level that corresponds to the stock’s maximum sustainable yield. Fishing above the overfishing limit for a stock would likely result in overfishing and jeopardize the capacity of the stock to produce maximum sustainable yield. For fish stocks where scientists are unable to estimate the maximum sustainable yield of a stock, regional fishery management councils (councils) sometimes choose not to specify an overfishing limit.

Step 2. The council’s Scientific and Statistical Committee recommends the stock’s acceptable biological catch. The acceptable biological catch is a catch limit that is adjusted downwards from the overfishing limit to account for scientific uncertainty. In cases where an overfishing limit has not been identified, the Scientific and Statistical Committee may recommend an acceptable biological catch based on historical catch levels that are considered sustainable.

Step 3. The council specifies the stock’s annual catch limit, which cannot exceed the Scientific and Statistical Committee’s recommendation for acceptable biological catch. The annual catch limit can be, and often is, set equal to the acceptable biological catch.

Step 4. The council has the option to set annual catch targets. Annual catch targets are used to account for management uncertainty in constraining catch below the annual catch limit.

Once annual catch limits or targets are specified, the council develops fishing regulations (e.g., gear restrictions, fish length limits, bag limits, seasons, etc.) to achieve those levels of catch. Councils also decide what types of accountability measures will be used in the event that annual catch limit or targets are exceeded to minimize delays in management actions.