Science Response 2015/038

Stock Assessment and Management Advice for BC Pacific Herring: 2015 Status and 2016 Forecast

Context

Fisheries and Oceans Canada (DFO) Pacific Fisheries Management Branch requested that DFO Pacific Science Branch assess the status of British Columbia (BC) herring stocks in 2015, and provide projections of potential herring abundance in 2016 and the consequences of a range of potential harvests to inform the development of the 2015/16 Integrated Fisheries Management Plan (IFMP).

Pacific herring abundance is currently assessed using a statistical catch-age-model. The catch-age model is fitted to commercial catch, proportions-at-age and fishery-independent survey index to estimate biomass and recruitment and to generate 1-year forecasts of spawning biomass (Martell et al., 2012; DFO 2014, 2015). A revised catch-at-age model was introduced for BC herring assessment in 2006 (Haist and Schweigert 2006), and the design of the model has since gone through several iterations to fix minor errors, as well as re-design and re-structuring of various model components.  One major change introduced in 2011 (Martell et al., 2012) was letting the model estimate the spawn survey scaling parameter q, rather than holding it fixed at q=1, as had been done in previous iterations of the catch-age-model. Another major change introduced in 2011 was to make the cut-off dependent on the model’s most recent estimate of unfished biomass, whereas it had previously been treated as a fixed quantity estimated from an earlier assessment model. Concerns have been raised regarding the application of these two changes relative to the historical management procedure (q=1 and fixed cut-offs), as well as requests to evaluate the potential consequences of these two management procedures (historical and current) using simulation. The potential consequences of these changes were not evaluated prior to their implementation, which along with lack of rebuilding in some areas has led First Nations and other stakeholders to question the appropriateness of the advice resulting from application of the current management procedure.

In May 2015, a closed loop-simulation tool was developed to evaluate performance of herring management procedures against a suite of conservation and fishery performance metrics. The simulation tool was reviewed in a May 2015 CSAS Regional Peer Review Process and accepted as a “proof of concept” that the methodology was sound. This simulation framework has immediate utility for this year’s stock assessment, because it aims to identify tradeoffs between management procedures that assume alternative ecological hypotheses about future conditions (e.g., future patterns of natural mortality and growth for herring) and assessment modeling assumptions (e.g., the proportion of the spawn observed by the survey).

This assessment separately addresses both the request to assess BC herring stock status and to compare approximations of historical and current management procedures using simulation. The status of BC herring stocks in 2015 and forecasts for 2016 are provided in the form of a stock assessment update, using Martell et al. (2012). Current stock status and trends, as well as projected biomass for 2016 are presented in the form of decision tables. Biomass estimates and decision tables reflect both the current management procedure (estimating q, time varying cut-offs) and an approximation of the historical management procedure (q=1, fixed 2014 cut-offs). The simulation study provides an initial evaluation of the relative performance of the two management procedures using metrics such as mean catch, variability in catch, and the probability of dropping below candidate limit reference points 0.25B₀, 0.30 unfished spawning biomass (B₀) (Pikitch et al. 2012) and 0.40B₀(Pikitch et al. 2012) for simulated approximations of the current and historical management procedures under alternate sets of assumptions. The simulation work is intended to guide interpretation of the assessment advice presented in Part 1, and to provide guidance for selection of an interim management procedure for the near term (1-2 years). The stock assessment and simulation analysis are presented in this Science Response.

The objectives of this Science Response are to:

Part 1
1. Assess the current status of Pacific Herring for each of the five major and two minor stocks using both the current (estimate q, time varying cut-offs) and historical management procedures (q=1, fixed cut-offs).
2. Present trends in herring biomass, depletion, and recruitment for each major and minor stock using both the current and historical management procedures;
3. Present probabilities of spawning biomass levels below cut-offs and harvest rates exceeding targets prescribed by both the current and historical management procedures for a range of 2016 allowable catch levels.

Part 2

4. Present simulation results comparing approximations of the current and historical management procedures against a range of conservation and fishery performance criteria (e.g. candidate limit reference points, yield, variability in yield).

Additional reference points and performance metrics are also included for the Central Coast, arising from discussions within the Heiltsuk-DFO Technical Team.

This Science Response Report results from the Science Response Process of September 2015 on Stock Assessment and Management Advice for BC Pacific Herring: 2015 Status and 2016 Forecast.

Complete document (PDF, 2,552  KB)

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