Modelling density on historical aggregation areas improves biomass estimates in yellow squat lobster off Chile

Yellow squat lobster fishery is one of the most important extractive activities in the central zone of Chile that occurs between 100 and 300 m deep. One of the difficulties in the management of the fishery is the high variability of the indices of abundance, which depends on the spatial distribution of the resource, among other things. Given the limited knowledge of spatial distribution patterns and spatiotemporal changes in yellow squat lobster density and biomass, the information collected during trawl survey assessments between 1999 and 2019 in central Chile was analyzed. Using the criteria of presence, persistence, distance, and discontinuity, 23 areas of aggregation between 26°42′ and 36°54′ S were identified and used to model the catch per unit area by a generalized additive models. The model explained 21.4% of the deviance and allowed us to show the population growth from 2001 onward between the regions of Valparaíso and Biobío, which was consistent with the extractive closure implemented by the managers from 32°10'S to the south. Most of the biomass of Cervimunida johni (∼75% of the biomass) was located in the Coquimbo, Puerto Oscuro, La Ligua, Valparaíso, Pichilemu, and Biobío aggregations, corresponding to 57% of the total surface where the resources were distributed. The present work provides information on the places that have been persistently occupied by Cervimunida johni, suggesting to managers an evaluation of the spatial limits that are currently being used in the surveys and their influence on the performance of the population evaluation model.