Improved VAST (vector autoregressive spatio-temporal) modelling of grenadier relative abundance in Subarea 48.6

In the present paper, we report progress since WG-FSA-2022 on the development of statistical modeling to estimate the abundance trends of grenadiers caught as bycatch in the longline fisheries in CCAMLR Subarea 48.6, using spatio-temporal delta generalized linear mixed models (GLMMs) implemented with R package “VAST”. Reflecting the suggestions from WG-FSA-2022, we developed a single model covering all research blocks and all fishing gears (trotlines and Spanish lines). Gear types were incorporated as a catchability covariate, and the index of abundance was estimated separately for each block. We recommend that future studies keep improving the VAST modelling for abundance of bycatch species in Subarea 48.6. Possible future tasks include the mapping of abundance to better understand the spatial patterns and the developing models for other bycatch species.