Research Document - 2013/080

Current Approaches for the Provision of Scientific Advice on the Precautionary Approach for Canadian Fish Stocks: Harvest Decision Rules

By A.R Kronlund, K.R. Holt, P.A. Shelton and J.C. Rice

Abstract

An essential component of the DFO decision-making framework is the inclusion of a harvest decision rule (or harvest control rule) in a management strategy.  The inclusion of a harvest decision rule satisfies a requirement of the Precautionary Approach (FAO 1995) and the DFO decision-making framework to specify in advance actions to be taken when specified deviations from operational targets and constraints are detected.  This document is intended as an aid to planning a more comprehensive process for developing harvest decision rule guidelines in Canada.  There are two types of rules in the DFO PA Framework:

1. a status-based rule where the intended removal rate is a piece-wise function of stock status, and
2. an acceptable risk-based rule in which the acceptable probability of stock decline is based on a combination of current stock status and the recent rate of change in stock status (i.e., increasing, stable, or declining).  

This document does not contain specific recommendations on the choice of risk tolerance and the relative priority of stock and fishery objectives.  The design of a stock-specific harvest decision rule should be considered in the context in which it is to be used.  Specific choices are dependent on a collaborative objective-setting process for the stock and fishery that involves assessment analysts, fishery managers, and resource stakeholders.

The design of a harvest decision rule need not explicitly incorporate fishery reference points.  This flexibility may be necessary to allow adjustments to fishing mortality over the entire range of stock status so the desired trade-off between conservation and economic performance can be achieved.  Complex decision rules should be avoided in favour of the simplest rule that will satisfy the preferred performance trade-offs.  Some jurisdictions have promoted the adoption of default, or generic, harvest decision rules that are expected to provide reasonably good performance over a wide range of fisheries.  However, there is no assurance that generic harvest decision rules will achieve stock-specific objectives.  Finally, harvest decision rules do not necessarily need to be limited to the status of a single target species; multi-species or ecosystem considerations can also be incorporated into rules.  However, experience with harvest decision rules that include multi-species or ecosystem considerations is limited in Canada, would require extensive development and testing prior to implementation and may require greater ecosystem level understanding than is currently available.

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