Exploratory development of a survey-based biomass index for ling (Molva molva) in ICES subareas 3, 4, 6-9 12 and 14. Working Document presented to the ICES Working Group on the Biology and Assessment of Deep Sea Fisheries Resources (WGDEEP) 30 April-6 May 2025, Thorshavn, Faroe Islands

We investigated options to develop an abundance index for ling (Molva molva) in ICES subareas 3, 4, 6-9, 12 and 14 using a Generalized Additive Model (GAM) with Tweedie distribution and a Vector Autoregressive Spatio-Temporal model (VAST; Thorson and Barnett, 2017). We used data from seven surveys, all conducted with a common sampling gear (GOV trawl) and coordinated under the ICES IBTS working group. Both models were investigated in multiple configurations, and we were able to identify models which produced adequate fits for both. The resulting indices were very similar to one another and also showed similar trends in recent years to the Norwegian commercial longline CPUE index that is currently used to assess this stock.