Research Document 2018/009
The Selection and Role of Limit Reference Points for Pacific Herring (Clupea pallasii) in British Columbia, Canada
By Kronlund, A.R., Forrest, R.E., Cleary, J.S., and Grinnell, M.H.
Abstract
This paper is focussed on the selection of limit reference points for the five major stocks of British Columbia Pacific Herring (Clupea pallasi) in partial fulfillment of requirements under the DFO PA Framework and as part of the commitment to renewal of the Pacific Herring management system. The international and Canadian policy basis for “best practice” limit reference points is reviewed in relation to the goal of avoiding “serious harm” to a fish stock. This paper uses an evidence-based approach to evaluate the concept of serious harm and to recommend limit reference points for British Columbia Pacific Herring stocks. Two analytical approaches for diagnosing serious harm are presented. First, production relationships for the five major stocks of Pacific Herring are inspected for persistent periods of low production and low biomass consistent with signs of possible serious harm. Second, theoretical equilibrium reference fishing mortality rates based on the concept of the replacement fishing mortality are investigated, as well as associated proxies based on maximum sustainable yield, spawning potential ratio and yield-per-recruit.
Pacific Herring stocks in the Central Coast, Haida Gwaii, and West Coast Vancouver Island management areas showed recent evidence of persistent low production, low biomass states that began by the mid-2000s and persisted for six to eleven years depending on the stock. These states were preceded by a transition to low production that began as early as the late 1990s from levels of comparatively high spawning biomass. The low spawning stock depletion levels reached during these periods was comparable to the levels estimated during the collapse of all five major stocks in the late 1960s, which was attributed to overharvest rather than loss of production.
The results of this study suggest that a persistent low production and low biomass state can occur at levels below 0.3 of the estimated equilibrium unfished spawning stock biomass for the Central Coast, Haida Gwaii and West Coast Vancouver Island stocks. A limit reference point of 0.3 of the unfished equilibrium spawning biomass is recommended for these stocks. The same limit reference point is recommended for the Prince Rupert District and Strait of Georgia stocks based on common life history and geographic proximity to the other three major stocks. Limit equilibrium fishing mortality rates based on the concept of replacement fishing mortality could not be recommended due to implausible estimates that were attributed in part to non-stationary conditions for natural mortality and size-at-age. It is also recommended that the introduction of limit reference points for Pacific Herring in British Columbia should adopt a management-oriented simulation approach to evaluating the consequences of reference point choices when evaluating alternative management options. It is recommended that management procedures designed to avoid breaching limit reference points and achieving desired targets be phased-in to smooth the transition from existing operational practice.
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