Effect in survey indices of removing stations in the NAFO closed Areas in the design of the EU surveys including the 2021 closed areas

In 2009, the Fisheries Commission established several coral and sponges protection closures areas to bottom fisheries within the NAFO Regulatory Area that started to be applied in 2010. Three random bottom trawl surveys are performed by the EU yearly in the NAFO Regulatory Area: Spanish Div. 3NO (Spring), Spanish and Portuguese in Div. 3M (Summer) and Spanish Div. 3L (Summer). The surveys are currently carried out by the R/V Vizconde de Eza and covers the closed areas. A study of the survey indices of the species assessed in NAFO (except shrimp) have been performed to know the impact of removing the hauls in the closed areas from the survey. The results of the analysis show that there are two species, Greenland halibut and roughhead grenadier, in which their biomass and/or age/length indices are affected in all the surveys analyzed. This is due to the fact that these two species are distributed at greater depths and that the closed areas are mainly found in deep areas, so the suppression of survey hauls in closed areas has a greater impact on the indices of these two species. The best way to know the impact in the assessment results of these changes in the Greenland halibut and roughhead grenadier indices would be to run the assessment with both indices, the base case ones and the new case ones, and compare the results. There are other species in which their global biomass indices do not change very much, but their age or length indices change appreciably when hauls from closed areas are removed from the calculations. In one case, the results of the assessment are compromised and it would be better to rerun the assessment with the new case indices to see the differences. In other cases, although the length distribution is not directly used in the assessment models, some recruitment and spawning stock biomass indices are derived from them, so changes in the perception of the stock could be encountered. These changes in the age/length indices should be considered in f