Benchmark workshop on Greenland halibut and redfish stocks (WKBNORTH)
The objective of this benchmark process was to propose and evaluate assessment methods and the data upon which they depend for the four stocks: 1) Greenland halibut in subareas 1 and 2; 2) Greenland halibut in subareas 5, 6, 12, and 14; 3) golden redfish in subareas 5, 6, 12, and 14; and 4) beaked redfish in Subarea 14 and Division 5.a. Greenland halibut in subareas 1 and 2 was previously assessed by the AFWG-Arctic Fisheries Working Group (Greenland halibut in subareas 1 and 2) using a Gadget model, while the others were assessed by the NWWG-Northwest Working Group using either a surplus production model (Greenland halibut in subareas 5, 6, 12, and 14), a Gadget model (golden redfish), or an ICES category 3 assessment method (beaked redfish).
For both Greenland halibut stocks, age data were sparse and diverse data sources were compiled to fit Gadget length- and age-based models, which was also sex dependent for Greenland halibut in subareas 1 and 2 due to sex-dependent life history variation. Both Gadget models were improvements from previous assessment methods, although the lack of age data creates high uncertainty. A SAM model was proposed for golden redfish, which was tuned using survey data from Iceland, Greenland, and the Faroe Islands. The SAM model showed better diagnostic results and resulted in higher current biomass levels than the previous model, but also confirms the previous view that recruitment has been consistently poor in recent years. Beaked redfish has sparse age data and was also assessed using the Gadget framework, tuned to surveys in Icelandic Waters, and indicates that the stock is below Blim and shows consistently low recruitment in recent years. It is recommended that migration and stock mixing be evaluated in future and that efforts be made to increase age data availability.
Reference points were calculated according to the ICES category 1 methods. Harvest control rules proposed and evaluated were based on the ICES MSY advice rule. The current harvest control rule used for golden redfish was considered precautionary.
Published under the auspices of the following ICES Steering Group or Committee