Exploring the influence of upwelling on the total allowed catch and harvests of a benthic gastropod managed under a territorial user rights for fisheries regime along the Chilean coast

Abstract

While there is a broad understanding of upwelling impacts on the functioning of marine ecosystems, empirical data that link this process to commercial species landings have not received the attention they deserve. The aim of this study was to explore the role of coastal upwelling in determining total allowable catch (TAC) and harvests of benthic fisheries, managed through a policy which assigns Territorial User Rights to Fishers (TURFs) along the Chilean coast. We used official historical TAC (217 TURFs) and harvest data (224 TURFs) for one of the most important benthic gastropod resources ("Loco", Concholepas concholepas) of the TURF system. TAC and harvest data ranged from 2001 to 2018 and were used to explore relations with an index of seasonal coastal upwelling, derived from a spatiotemporal decomposition, of sea surface temperature along the same study areas and period. Using Bayesian generalized linear multilevel models (TURFs as group-level effect), we showed a positive and significant effect of the upwelling over TAC and harvest of Loco. Model results explained 47% of TAC and 34% of harvests. The effects of upwelling were comparatively stronger to the effects of the area (hectares) and the number of fisher members of the TURF. In addition, models estimates showed negative inter-annual trends during the study period, for TAC and harvests, and that these differed as function of upwelling variability. Understanding the role of upwelling gives objective criteria to begin addressing the differential role that social and environmental aspects play in overall TURF performance, allowing to begin hypothesizing over socially driven deviances from predicted patterns.