Science Advisory Report 2020/024

Evaluation of Potential Rebuilding Strategies for Outside Yelloweye Rockfish in British Columbia

Summary

• This paper provides advice on rebuilding Outside Yelloweye Rockfish (OYE, Figure 1) using closed-loop simulation modelling to test performance of a set of candidate management procedures (MPs) against specific quantitative objectives.
• Due to differences in perceived abundance and exploitation history, the OYE stock was divided into two sub-regions (North and South, Figure 1) for these analyses.
• The key components of this closed-loop simulation work are:
  1. development of a two-area component (North/South) hierarchical age-structured operating model for OYE that represents a range of hypotheses about natural mortality and exploitation history using different data scenarios,
  2. testing MPs comprised of monitoring data, assessments, and harvest control rules (HCR) used to implement rebuilding policies, and 3. evaluating performance measures that are used in determining the expected conservation performance of alternative MPs relative to stated rebuilding objectives.
• The Rebuilding Objectives being evaluated are:
1. to grow the spawning stock biomass (SSB) out of the critical zone (i.e., above the limit reference point (LRP) of 0.4BMSY, where BMSY is the operating model biomass at MSY), with a very low (5%) probability of further decline, measured over 1.5 generations (57 years); and
2. when the SSB is between 0.4BMSY and 0.8 BMSY, limit the probability of decline over the next 10 years from very low (5%) at the LRP to moderate (50%) at BMSY. At intermediate stock status levels, define the tolerance for decline by linearly interpolating between these probabilities.
   • A generation time of 38 years for OYE was used, corresponding to the average age of the modeled unfished spawning stock.
   • Model estimates of spawning biomass depletion relative to unfished levels (estimated for 1918) range from 29-51% in the North, 21-43% in the South, and 27-48%, coast-wide.
   • Alternative data scenarios produced a wide range of estimated stock status, as well as biological and management parameters, from which 4 representative operating model scenarios were selected for simulation testing MPs.

   The candidate MPs evaluated included three different assessment methods:

   1. a catch-at-age assessment model (CAA),
   2. a surplus production assessment model (SP), and
   3. an empirical rule using survey index trends (IDX).
3. The three assessment methods were used in combination with different harvest control rules or implementation error scenarios to create a set of candidate MPs that were simulation tested for each of the 4 operating model scenarios for North and South areas independently.
4. Simulations of MP performance for setting future OYE Total Allowable Catches (TACs) generally showed robust performance relative to the objectives described above, across the range of operating model scenarios. • All operating model scenarios implied that OYE is currently above 0.4BMSY coast-wide even though OYE biomass declined rapidly by 49-71% in the North, and by 57-79% in the South over the past two OYE generations.
5. Several potential MPs were identified that could increase or stabilize OYE biomass in both North and South areas. However, it is not possible at this time to recommend a specific MP for each area without further guidance on fishery objectives and timelines from OYE managers, First Nations, and fishery stakeholders.

This Science Advisory Report is from the October 29-30, 2019 regional peer review on the Evaluation of Management Procedures for the Outside Population of Yelloweye Rockfish Rebuilding Plan. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Scheduleas they become available.

Science Advisory Report 2020/024 (PDF, 1,415 KB)

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