Redfish (Sebastes mentella and Sebastes fasciatus) stocks assessment in units 1 and 2 in 2021

Abstract

Redfish landings in 2020-21 were 1,130 t in Unit 1 (20% of the combined quota in the experimental and index fisheries) and 5,787 t in Unit 2 (68% of the TAC). Large numbers of regulatory-sized fish between 22 to 26 cm in length have entered the fishery in Unit 1 (since 2018) and Unit 2 (since 2019). Annual landed bycatch is a low proportion of total landings in Redfish fisheries. Bycatch includes commercial species and species of conservation concern. The impact of bycatch in Redfish fisheries has not been evaluated for all species. Fishing deeper than 300 m can reduce catches of S. fasciatus in all fishing areas except the Laurentian Fan, and reduce catches of under-sized (< 22 cm) Redfish. Simulations of bias in the species identification process and available genetic information on the relative abundance of the two species suggest the biomass of S. fasciatus in research surveys may currently be overestimated. The Unit 1 (2021) total estimated survey biomass for S. mentella (2,805 kt (2,133-3,549 95% CI)) remained among the highest values in the time series beginning in 1984, while S. fasciatus (420 kt (118-722 95% CI)) was at the highest value recorded. The Unit 2 (2018 – most recent calibrated survey) total estimated biomass for S. mentella (805 kt (607-1089 kt 95% CI)) was the highest value recorded in the time series beginning in 2000, while S. fasciatus (101 kt (0-352 kt 95% CI)) was below the series mean. Fish larger than the minimum regulatory size (22 cm) accounted for a large fraction of total survey biomass in Unit 1 in 2021 (93% for S. mentella and 85% for S. fasciatus) and 89% of the total survey biomass of both species in Unit 2 in 2018. Individuals from the strong 2011-2013 cohorts of S. mentella and S. fasciatus currently exhibit a reduced growth potential and are maturing at smaller sizes than previously observed strong cohorts. The empirical limit reference point (LRP) for each stock was updated based on current maturity information used to estimate spawning stock biomass from 2011 onwards. The revised LRPs are 44 kt for S. mentella and 30 kt for S. fasciatus. In 2021, the spawning stock biomass of S. mentella would be in the Healthy Zone based on the proposed upper stock reference (USR). The magnitude of the increase in spawning stock biomass of S. fasciatus is uncertain, but evidence indicates the stock is at least above the LRP. Short-term prospects for Redfish stocks in Units 1 and 2 are generally positive. High biomass of S. mentella allows for increased harvests, while caution is warranted for S. fasciatus and bycatch species.