1 Introduction

The South Atlantic Fishery Management Council has started a Management Strategy Evaluation (MSE) process for the Snapper-Grouper fishery, currently managed under the Snapper-Grouper Fishery Management Plan. The Snapper-Grouper fishery includes 55 species of snappers, groupers, and other species.

This document describes the technical specifications of the MSE process. It is a living document that will be continually updated to reflect the current state of the MSE work. Comments, questions, and feedback are welcome by contacting the MSE Technical Group Members.

More information on the MSE process can be found on the SAFMC Snapper-Grouper MSE homepage.

There are three main components in an MSE analysis:

1. Operating Models (OMs)

   Operating models contain a mathematical description of the fishery system, including the biology of the fish stock, the historical exploitation pattern by the fishing fleet(s), and the observation processes used to collect the fishery data. The OMs also include the assumptions for the data collection process in the forward projections, and any implementation error for implementing the management advice in the forward projections.

   An MSE process usually includes a number of different operating models, each representing a different hypothesis about the potential fishery dynamics. The OMs should span the key uncertainties in the fishery system. By including these uncertainties, the MSE can identify a management approach that is robust to these uncertainties.

2. Management Procedures (MPs)

   Management procedures are a set of rules that convert fishery data into management advice, e.g., a total allowable catch limit (TAC), a size limit, an effort control, a spatial closure, or some combination of different management measures. The main goal of MSE is to evaluate the performance of different MPs and identify the MP that is most robust to the uncertainty in the system.

3. Performance Metrics (PMs)

   Performance metrics are used to evaluate the performance of the management procedures. PMs are quantitative metrics than can be calculated within the MSE framework and be used to evaluate and compare the performance of the CMPs.

2 The SAMSE R Package

All code related to the MSE process is available in the SAFMC-MSE Github Repository.

The SAFMC-MSE Github Repository includes an R package called SAMSE, which contains all code for running the closed-loop simulations and examining the results. This package can be installed directly from GitHub:

install.packages('remotes')
remotes::install_github('blue-matter/SAMSE')

The SAMSE package uses openMSE framework. openMSE is an R package that has been developed for conducting fast, flexible, and transparent, MSE for a wide range of fisheries. openMSE is an umbrella package that includes the MSEtool, SAMtool and DLMtool packages. A non-technical description of openMSE and its key features is available on the openMSE website.

The operating model in openMSE, including assumptions and equations, is described in detail in Carruthers and Hordyk, 2018.

3 Species included in the MSE

The MSE process is currently focused on three species:

1. Red Snapper (Lutjanus campechanus)

2. Gag Grouper (Mycteroperca microlepis)

3. Black Sea Bass (Centropristis striata)

The MSE framework has been designed so that it can be easily expanded to include additional species.

The most recent stock assessments for these three stocks are SEDAR 73, SEDAR 71, and SEDAR 76 for Red Snapper, Gag Grouper, and Black Sea Bass respectively.

The fisheries are managed under the Snapper-Grouper Fishery Management Plan, which includes snappers, groupers and related demersal species of the continental shelf of the SE United States exclusive economic zone (EEZ), extending from the North Carolina/Virginia border through to the Atlantic size of the Florida Keys 83° W longitude (Figure 3.1).

Figure 3.1: The geographical area of management for the South Atlantic Fishery Management Council.

4 Process for Generating Operating Models

The operating models (OMs) used in the MSE are age-structured, with for spatial structure and age-based movement. The OMs were generated by importing the most recent assessments (SEDAR 73, SEDAR 71, and SEDAR 76 for Red Snapper, Gag Grouper, and Black Sea Bass respectively) into the MSE framework. The assessments were conducted with the Beaufort Assessment Model (BAM) and the fishery dynamics in the operating models exactly matched the output of the stock assessments.

A full description of the process used to generate the operating models, including the code to reproduce the operating models, are available here. Operating models for other species can be added to the MSE framework by following this process.

5 Base Case Operating Model

The Base Case operating model was based directly on the respective SEDAR assessments for each species, following the process described above. This section summarizes the main properties of the Base Case OM.

Alternative operating models are developed as modifications of the Base Case OM. These alternative operating models are intended to span the critical uncertainties in the knowledge of the fishery systems, and are described in Section 8.

5.1 Selectivity and Retention Schedules

Figure 5.1 show the selectivity- and retention-at-age curves in the last historical year for each of the stocks in the multi-species operating model.

The selectivity and retention curves remain the same in the projection period unless changed by a management procedure. Retention curves with a maximum value less than one indicate a general level of discarding.

Figure 5.1: The selectivity- (solid), retention-at-age (dashed), and dead discard (dotted) curves for three stocks in the multi-species operating model. The plot shows the curves from the terminal year of the assessments. The dash-dot grey line shows the maturity-at-age schedule for each stock.

5.2 Removals, Landings, and Discards

Figure 5.2 shows the historical overall landings and discards for the multi-species Base Case operating model. Figure 5.3 shows the historical overall landings and discards by fleet.

Figure 5.2: The overall landings and dead discards (1,000 lb) from the historical period the multi-species operating model.

Figure 5.3: The landings (1,000 lb) by fleet from the historical period of the multi-species operating model. Note the different scale on the y-axes.

5.4 Biomass and Reference Points

Figure 5.4 shows the historical spawning biomass, as estimated by the assessments, relative to the rebuilding targets for each stock.

Figure 5.4: The historical spawning biomass relative to the rebuilding target for each stock. The horizontal lines indicate the reference points.

6 Spatial Structure

The SEDAR assessments do not include spatial structure. Consequently, information on the spatial distribution and movement of the stocks has to be obtained from elsewhere, and the spatial structure added into the operating model developed from the SEDAR assessments.

The spatial structure of the MSE has been defined as 6 areas, including 3 geographic regions (Figure 6.1) and a Nearshore (<100ft) and Offshore (>100ft) component for each region (black line in Figure 6.1).

Figure 6.1: The six spatial areas defined in the MSE, with three geographic regions (colors) and a division of each in Nearshore (<100ft) and Offshore (>100ft) (black line).

7 Assumptions for Projection Dynamics

7.1 Recruitment Process Error

The variance-covariance matrix was estimated from the historical log recruitment deviations of each species in the analysis. A truncated multivariate normal distribution, truncated at 2 standard deviations, was then used to generate correlated random log recruitment deviations for the projection period, with the standard deviation and lag-1 auto-correlation factor reported by the stock assessments (Figure 7.1).

Figure 7.1: Scatter plots of the log recruitment deviations for each stock.

Figure 7.2 shows an example of the historical and projection recruitment deviations for the three stocks in the operating model.

Figure 7.2: An example of the recruitment deviations for a single simulation for the three stocks in the Base Case OM. The blue lines indicates the recruitment deviations during the historical period (identical across all simulations). The green lines indicates the recruitment deviations in the projection period.

8 Additional Operating Models

The additional operating models are developed as variations of the Base Case OM, and are intended to span the key uncertainties in the understanding of the fishery system.

The uncertainties considered in the additional operating models have been identified from the most consequential sensitivity tests in the recent stock assessments, and from discussions with the Snapper-Grouper Advisory Panel.

Currently 6 operating models (including the Base Case) have been developed. Table 8.1 provides a summary of the operating models. The sub-sections below describe more details for each of the additional operating models.

9 Performance Metrics

Four performance metrics have been defined to calculate the relative performance of the alternative management approaches (Table 9.1).