Ecological basis to embrace temporal assessment and spatial management of the European hake (Merluccius merluccius) in the northern Iberian Peninsula

IMBeR Future Oceans 2, 17-21 June 2019, Brest, FranceSpatial management of commercial resources is becoming an effective measure to be broadly implemented in the European Seas. However, it is currently unconnected from the population dynamics and the temporal assessment. Indeed, it is known that species abundance can be influenced by the environmental features of its own habitat and/or by biotic process that are spatially structured (e.g. reproduction, predation, among others). Usually, this variability is assumed to be implicitly in the abundance trends used as inputs of the stock assessment models and it is not explicitly taken into account. Within this context, in this study we propose a novel methodological approach for an effective implementation of spatial and ecological knowledge that could help to embrace species spatial management in an operational way, providing a more holistic and ecosystem-based approach. As case study we used the European hake (Merluccius merluccius) in the northern continental shelf of the Iberian Peninsula. Hake data in functional groups by size collected during the scientific survey series “DEMERSALES” by the “Instituto Español de Oceanografía” (IEO) from 1993 to 2017 were analyzed using Bayesian hierarchical spatial-temporal models (B-HSTMs), considering as environmental variables Sea Temperature, Sea Salinity, bathymetry and rugosity of the seabed. B-HSTMs link spatially information on hake abundance to environmental variables to estimate and predict where (and how much of) this species is likely to be present in the studied area in a specific year. Indices of abundance obtained as outputs from B-HSTMs, performed with the innovative integrated nested Laplace approximation (INLA) methodology and software, are then used as inputs for the GADGET (Globally applicable Area Disaggregated General Ecosystem Toolbox) stock assessment model. Finally, a comparative analysis of the results obtained with the GADGET model using the B-HSTMs abundance indexes and the ones commonly used in stock assessment evaluations is performed. We argue that the analytical framework proposed in this study allowed to (1) assess which environmental factors influence the different size groups of the hake in the northern continental shelf of the Iberian Peninsula, (2) identify the areas in which the different functional groups are more aggregated and their spatial-temporal fluctuations, and (3) could be a decisive step to improve habitat-based standardization abundance indexes and stocks’ management in European SeasPeer reviewe