Science Response 2018/023
Harvest Control Rule Update for Western Component Pollock (Pollachius virens) in NAFO Divisions 4Xopqrs5
Context
Pollock (Pollachius virens) in Northwest Atlantic Fisheries Organization (NAFO) Divisions 4VWX5 comprise two population components: a slower-growing Eastern Component including Divisions 4V and 4W, as well as Subdivisions 4Xm and 4Xn, and a faster-growing Western Component (WC) including 4Xopqrs and Canadian portions of Area 5. The WC has been the main focus of past analytical assessments, but scientific advice on stock status and catch limits using Virtual Population Analysis (VPA) modeling has been highly variable, especially since the mid-2000s. For example, the 2008 assessment indicated that Age 4+ population biomass was at 27,000 tonnes (t) (Stone et al. 2009) while the 2010 assessment update indicated Age 4+ population biomass was either 23,000 t or 17,000 t, depending on whether the very low 2010 Fisheries and Oceans Canada (DFO) Research Vessel (RV) Summer Survey indices were excluded or included in the analysis (Stone 2011). Consequently, the Canadian fishing industry recommended exploration of alternative approaches, which would provide more stability in future catch limits to allow for better business planning and a more stable fishery.
In 2011, fisheries managers and the fishing industry decided to manage WC Pollock using a risk-management approach and embarked on a Management Strategy Evaluation (MSE) process, with the help of government scientists and outside experts (DFO 2011). MSE is a technique to explicitly consider the uncertainty in stock assessment assumptions and models, and to compare the likely consequences to Management Objectives when a predetermined Management Procedure (MP) incorporating a Harvest Control Rule (HCR) is applied. The Pollock MP was selected on the basis of satisfying three medium-term objectives agreed upon for management of the resource, which relate to sustainability, catch levels and the extent of annual catch changes. The MP model was built around a HCR that either increased or decreased future catch limits based on results from ongoing monitoring from the annual DFO Summer RV Survey. An Exceptional Circumstances Protocol was put in place to cover situations that fall outside the range for which the MP was simulation tested and, if necessary, to allow for some form of intervention.
The 2015 Science Response Process recommended a catch limit of 2,225 t for WC Pollock for fishing year (FY) 2016-2017 (DFO 2016). Discussions following the process centered around an irregularity in the 2015 DFO Summer RV Survey, increases in Pollock indices from the U.S. National Marine Fisheries Service (NMFS) Spring and Fall surveys in Canadian waters since 2013, and an increasing proportion of commercial catch coming from 5Z, an area without consistent coverage by the DFO Summer RV Survey. Given all of these concerns, Resource Management implemented a 9% increase in the quota and temporarily suspended the use of the HCR with the intent to review and consider other sources of information when generating catch advice for 2017/2018. The 2016 Science Response Report (DFO 2017) provides a review of additional indices of WC Pollock biomass from the NMFS Spring and Fall Surveys, and recent DFO Summer RV Survey coverage of eastern Georges Bank. Updated information on commercial catch at age, fish condition and mean lengths at age were also examined.
In January 2017, Resource Management and Industry asked that the 2015 RV Survey index value be considered a missing value to reflect concerns that the point was not representative of the state of the stock. Further, as the HCR uses the previous year’s quota as a starting point for the following year, the actual 2016/17 quota of 3,081 t was used in the HCR to generate advice for 2107/18. This approach was supported by members of the Scotia Fundy Groundfish Advisory Committee as it stayed as close as possible to the HCR for this stock, while reflecting the increasing trends seen in the DFO Summer RV Survey index, the fishery, and U.S. surveys. Following this approach, the HCR quota for FY 2017/2018 was set at 3,697 t.
This report provides an update to the 2016 analysis (DFO 2017) of the Western Component Pollock Harvest Control Rule and provides advice on the FY 2018/2019 catch limit generated by the Pollock MP and HCR using updated information from the 2017 DFO Summer RV Survey. It also describes current status with respect to the provisions in the Exceptional Circumstances Protocol. Following the approach accepted at the 2016 Science Response Process, the HCR with updated monitoring data for 2017 generated a catch limit of 4,437 t for FY 2018/2019, up 20% from 3,697 t for FY 2017/2018. The DFO Summer RV Survey biomass index decreased from 28.15 kg/tow in 2016 to 13.16 kg/tow in 2017 and did not trigger the exceptional circumstance provision of the DFO Summer RV Survey biomass index being < 6 kg/tow for two consecutive years and the Survey Index Ratio being < 0.2.
This Science Response Report results from the Science Response Process of December 4, 2017, on the Status Update of the Western Component Pollock Management Strategy Evaluation.
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