What are harvest control rules?
Harvest control rules (HCRs) are the operational component of a harvest strategy, essentially pre-agreed guidelines that determine how much fishing can take place, based on indicators of the targeted stock’s status. HCRs range from basic, constant catch strategies—under which catch levels do not change—to complicated, multistep rules that set allowable catch based on triggers.
Empirical vs. Model-Based Harvest Control Rules
Empirical HCRs: Indicators on which fishing opportunities are set come from one or more direct measures of stock status, such as:
- An abundance survey
- A catch per unit effort (CPUE) index: The amount of catch taken per unit of fishing effort, such as the number of fish per 1,000 hooks. Often used as a proxy for stock abundance.
Model-based HCRs: Indicators are based on models, such as:
- An abundance level that is estimated by a stock assessment model
How a Harvest Control Rule Works
Stock status can be represented graphically by what is known as a Kobe plot. The example below shows a basic HCR. The fishery’s ideal state is green, its cautionary state is yellow, and the state to avoid is red. The HCR has the following specifications:
- If biomass is below BLimit, suspend the fishery and institute a scientific monitoring quota until the limit is reached or exceeded.
- If biomass is between the limit (BLimit) and the target (BTarget), reduce fishing mortality in accordance with the rebuilding phase of the HCR.
- If biomass is greater than or equal to the target (BTarget), fish at the target mortality rate (FTarget).
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