Science Advisory Report 2019/036

The identification of provisional reference points and harvest rate options for the commercial Red Sea Urchin (Mesocentrotus franciscanus) fishery in British Columbia

Summary

• An annual harvest rate of 2%, derived using a modified Gulland surplus production model (Gulland 1971; Leus et al. 2014), has been used as part of the Red Sea Urchin (RSU) Assessment Framework for most of the BC coast since 1994. The accumulation of a substantial amount of biological data on RSU in BC allows for the development of new models and warrants a re-evaluation of the impact of the current 2% harvest rate.
• Previously published biological parameters using British Columbia (BC) fishery-independent data and a new length-based simulation modelling approach were used to provide advice on the application of a range of possible RSU commercial fishery harvest rates for Haida Gwaii (Pacific Fishery Management Area [PFMA] 1, 2, 101 and 102), the Mainland North Coast (PFMAs 3 to 10 and 103 to 110), and the South Coast Inside Waters between Vancouver Island and the Mainland (PFMAs 11 to 20, 28, 29 and 111).
• To evaluate the impact of the range of harvest rates, the concept of serious harm was considered in the identification of a provisional Limit Reference Point (LRP) and Upper Stock Reference (USR). Reference Points were not previously identified for BC’s RSU commercial fishery, and the current work aligns this fishery with the Sustainable Fisheries Framework (DFO 2009a) and DFO’s Fishery Decision-Making Framework Incorporating the Precautionary Approach (DFO Precautionary Approach) (DFO 2009b).
• An empirical approach was used for establishing Reference Points, based on RSU density estimates in Sea Otter (Enhydra lutris) inhabited areas. Areas where Sea Otters have been present for several years may indicate the highest harvesting pressure under which biologically viable RSU populations can be maintained. The estimated RSU mean densities in areas of California, Washington State and BC where Sea Otters have been established for at least five years, ranged from 0 to 1.13 RSU/m2 (Table 1) and reference points were developed using a locally relevant, long-term data set (Watson and Estes 2011).
• The recommended LRP and USR are 0.3 mature RSU/m2 and 0.6 mature RSU/m2, on RSU habitat, respectively; mature RSU are defined as ≥ 50 mm test diameter and RSU habitat is defined as hard substrate larger than gravel (>0.25 cm), where mud is not the predominant substrate.
• New length-based population models were developed, and mature density estimates were projected forward 100 years using statistical length-based simulation models. Decision tables showing the probability of breaching Reference Points after varying time periods and for a range of harvest rates (2-24%) were provided to inform Fisheries Management decisions.
• The results for the 100th year of the model simulations are shown as an example from the simulation range (Table 2), and Fisheries Managers can choose to implement management actions from the range of simulated results, according to management objectives.
• RSU populations are above the USR in Haida Gwaii, the Mainland North Coast, and the South Coast Inside Waters between Vancouver Island and the Mainland, individually and when they are combined.

This Science Advisory Report is from the Feb 13, 2019 Identification of candidate reference points and harvest rate options for the commercial Red Sea Urchin (Mesocentrotus franciscanus) fishery in British Columbia. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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