1 Introduction
This document describes the trial specifications for the Management Strategy Evaluation (MSE) of South Atlantic albacore tuna (Thunnus alalunga), undertaken for the International Commission for the Conservation of Atlantic Tunas (ICCAT).
This is a living document and will be updated as the MSE process progresses.
1.1 MSE Framework
The MSE is built on the openMSE framework (MSEtool v4+). All functions and code for reproducing the operating models, management procedures, and performance indicators are contained in the iccatSALB R package and its associated GitHub repository. The analysis itself is carried out through a set of scripts that call on these functions, which are also available in the repository alongside the package.
1.2 Stock Assessment
The operating models are conditioned on the ICCAT South Atlantic albacore stock assessment, fitted using Stock Synthesis 3 (SS3) v3.30.23.1 (Methot and Wetzel 2013), referred to here as the S05 model run.
TBD: link the assessment report once published
1.2.1 Data
The S05 assessment is fit to catch and abundance index data from 1956–2024, comprising:
- 5 catch fleets (
Fleet_01–Fleet_05) - 5 CPUE/abundance indices:
Indx_CTP-LL_TB1(Chinese Taipei longline, time block 1)Indx_CTP-LL_TB2(Chinese Taipei longline, time block 2)Indx_JPN-LL_TB2(Japan longline)Indx_BR_URY-LL(Brazil/Uruguay longline)Indx_ZAF-BB(South Africa baitboat)
1.2.2 Model Structure
- Model years: 1956–2024 (69 years)
- Areas: 1 (single area, no movement)
- Sexes: 1 (combined-sex model)
- Ages: 0–15, with age 15 as the plus group
1.2.3 Fixed Biological Parameters
The S05 model uses the following fixed/estimated biological parameter values:
| Parameter | Value |
|---|---|
| Natural mortality (M) | Lorenzen, reference M = 0.36 at reference age 11 |
| Growth model | von Bertalanffy |
| L at Amin (age 0) | 23.17 cm |
| L∞ (L at Amax) | 121.24 cm |
| von Bertalanffy K | 0.238 |
| CV (young) | 0.125 |
| CV (old) | 0.125 |
| Weight-length a | 1.3718e-05 |
| Weight-length b | 3.0793 |
| Maturity option | Age logistic |
| Age at 50% maturity | 5 |
| First mature age | 4 |
| Stock-recruitment functional form | Beverton-Holt |
| Steepness | 0.75 (fixed) |
| σR | 0.4 (fixed) |