Representing Atlantic Cod (Gadus morhua) Population Structure Using Spatiotemporal Standardization of Fishery Catch Rates.

McGinnis, Lucy¹*, Keith Hankowsky¹, Max Grezlik¹, Alex Hansell² Gavin Fay¹, Steve Cadrin¹, ¹University of Massachusetts, Dartmouth, School for Marine Science and Technology, New Bedford, MA, ²NOAA Northeast Fisheries Science Center, Woods Hole, MA

Indices of abundance based on fishery independent survey data are preferred in stock assessments compared to fishery catch rates because they are designed to be representative of stock trends. However, fishermen collect data at a higher spatiotemporal resolution which, when standardized to remove effects of variables other than abundance, can potentially supplement information from a survey index. Updated understanding of the stock structure of Atlantic cod (Gadus morhua) supports shifting from two assessed management units to five populations. This change requires fine scale data, especially for populations with small sample size in the NEFSC Bottom Trawl Survey. We compare methods for producing indices of abundance for cod from vessel logbook data. First, data were divided into spatial units at the management level and the population structure. Generalized linear models (GLMs) were fit with covariates including combinations of year, month, depth, vessel horsepower, vessel tonnage, and mesh size. An optimal model for each spatial unit was selected, and indices were produced from the transformed year effects. Trends in abundance differed between populations within the management units. Model fits were better for population units than management units, but predictive performance was poor for populations with low sample sizes. Second, a hierarchical model fit to the entire region will assess if uncertainty can be reduced by sharing information among spatial units. Results will contribute to the ongoing 2023 Atlantic Cod Research Track Stock Assessment and the index standardization methods explored are relevant to other groundfish stock assessments.