Draft integrated stock assessment for the Heard Island and McDonald Islands Patagonian toothfish (Dissostichus eleginoides) fishery in Division 58.5.2

Recommendations

1. That Model 2 presents best available science for the 2021 Patagonian toothfish stock assessment in Division 58.5.2.
2. That CCAMLR set a catch limit of 3010 tonnes for 2021/22 and 2022/23 in CM 41-08 based on the result of this assessment and the CCAMLR decision rules.

Abstract

This paper presents an updated assessment for the Patagonian toothfish (Dissostichus eleginoides) fishery at Heard Island and McDonald Islands (HIMI) in CCAMLR Division 58.5.2 with catch until the end of 2021 and observations until the end of 2020. The updated assessment model is based on best available estimates of model parameters, the use of abundance estimates from a random stratified trawl survey (RSTS), longline tag-release data from 2012-2019 and longline tag-recapture data from 2013-2020, and auxiliary commercial composition data to aid with the estimation of year class strength and selectivity functions of the trawl, longline and trap sub-fisheries.

Compared to the 2019 assessment that was accepted by WG-FSA-19 to be used for management advice, this assessment takes into account (1) update the model with catch data to 2021 and observations to the end of 2020 including new ageing data from the RSTS and commercial fishery, and (2) updated growth parameters. All model runs were conducted with the CASAL version 2.30-2012-03-21 rev. 4648 that was agreed on by WG-SAM-14.

The estimates of this stock assessment were similar to those from the 2019 assessment (Ziegler 2019a). The updated assessment model led to a slightly smaller estimate of the virgin spawning stock biomass B₀ than that obtained in 2019, with an MCMC estimate of 69 210 tonnes (95% CI: 64 811-74 758 tonnes). The estimated SSB status at the end of 2021 was 0.45 (95% CI: 0.44-0.47), in line with the projection from the 2019 stock assessment.

The comprehensive monitoring program of the HIMI toothfish fishery will continue to include a tag-recapture program, annual trawl surveys, and extensive fish ageing to consolidate and estimate recent trends in biomass and YCS.

Based on the result of this assessment and the CCAMLR decision rules, we recommend that CCAMLR set a catch limit of 3010 tonnes for 2021/22 and 2022/23 in CM 41-08 for the Patagonian toothfish fishery in Division 58.5.2.