Science advice on guidance for limit reference points under the fish stocks provisions

Abstract

The Limit Reference Point (LRP) represents the upper bound of stock states that should be avoided in order to prevent serious harm to the stock and is the boundary between the Critical and Cautious zones of DFO’s Precautionary Approach (PA) Policy. Under that Policy and the Fish Stocks Provisions (FSPs), breaching the LRP is a trigger for a rebuilding plan. Serious harm is an undesirable state that may be irreversible or only slowly reversible over the long-term. It may be directly or indirectly due to fishing, other human-induced impacts, or natural causes, and occurs at states before extirpation is a concern. Loss of stock structure (e.g., depletion of subunits) is not typically included in descriptions of serious harm but can meet the definition of serious harm if it constitutes a loss of stock productivity or resilience. A stock can be defined based on the management unit, assessment unit, and/or biological unit. Scale mismatch occurs when there is misalignment in time or space between these units, management or assessment activities, or biological processes. Consequences of scale mismatch can include over- or under-estimation of stock biomass and exploitation rates, as well as impacts to reference points, stock status metrics, and the risk of serial depletion of subunits. Best-practice principles are provided to give overarching guidance and recommendations for selecting, estimating and updating indicators, LRPs and stock status metrics under the PA Policy and FSPs. These encompass scenarios ranging from data-rich to data-limited, where more than one indicator or model may be used for advice, where scale mismatch may be occurring or where the perception of stock status has changed between assessments. Future revisions to Canadian harvest strategy policy should include default guidance for LRPs based on estimates of unfished biomass. Gaps were identified for future work, predominately related to non-stationarity in conditions affecting productivity when defining LRPs, as well as spatial reference points, the impact of climate forcing on scale mismatch, and for situations when it may be desirable to set an LRP that accommodates ecosystem functions.