Working Group on Improving Survey Data for Aanalysis and Advice (WGISDAA; outputs from 2021 meeting)

The Working Group on Improving use of Survey Data for Assessment and Advice (WGISDAA) deals with various topics related to survey data such as experimental survey design, analysis of survey data, and its use in assessment models. The working group serves to bring together experts in data collection and statistical analysis and stock assessment in order to ensure the best possible science.

WGISDAA reviewed a new combined survey index for Northern Shelf haddock based on a Delta-GAM model. The new index combines the North Sea International Bottom Trawl Survey (NS-IBTS) survey with the surveys west of Scotland and thus provides a more complete coverage of the stock. The new index has improved internal consistency compared to any of the surveys used in isolation and should thus be considered for the upcoming benchmark.

The effect of bottom oxygen conditions on survey catch rates of cod and plaice in the Baltic Sea were examined. Low oxygen conditions were hypothesized to be the cause of low catch rates in 2019 by the Baltic Working Group (WGBFAS). While significant effects of oxygen conditions were found for both species, plaice was found to be tolerant of borderline hypoxic conditions. It was noted that record high catches of plaice occurred in 2014 and 2015, where oxygen conditions were the worst in the time series. Oxygen conditions did therefore not seem to be the cause of low catches of plaice in 2019. Survey indices for Western Baltic cod from a model that included bottom oxygen showed very little difference compared to the currently used indices.

WGISDAA reviewed plans for the upcoming Workshop on Unavoidable Survey Effort Reduction (WKUSER2) and recommended future directions. Additionally, preliminary work on survey indices for three North Sea species were presented: plaice, starry ray, and horse mackerel, and potential further analyses were discussed.