15 pages, 5 figures, 1 table.-- This article is licensed under a Creative Commons Attribution 4.0 International License,, Information on temporal variations in stock reproductive potential (SRP) is essential in fisheries
management. Despite this relevance, fundamental understanding of egg production variability remains
largely unclear due to difficulties in tracking the underlying complex fluctuations in early oocyte
recruitment that determines fecundity. We applied advanced oocyte packing density theory to get
in-depth, quantitative insights across oocyte stages and seasons, selecting the commercially valuable
European hake (Merluccius merluccius) as a case study. Our work evidenced sophisticated seasonal
oocyte recruitment dynamics and patterns, mostly driven by a low-cost predefinition of fecundity as a
function of fish body size, likely influenced also by environmental cues. Fecundity seems to be defined
at a much earlier stage of oocyte development than previously thought, implying a quasi-determinate
– rather than indeterminate – fecundity type in hake. These results imply a major change in the
conceptual approach to reproductive strategies in teleosts. These findings not only question the current
binary classification of fecundity as either determinate or indeterminate, but also suggest that current
practices regarding potential fecundity estimation in fishes should be complemented with studies on
primary oocyte dynamics. Accordingly, the methodology and approach adopted in this study may be
profitably applied for unravelling some of the complexities associated with oocyte recruitment and
thereby SRP variability, This work was funded by the Spanish research grant DREAMER, Recruitment Dynamic
of European Hake (CTM2015-66676-C2-1-R). A.S. would like to thank the Annenberg Foundation, CA, USA
(Grant No. 16-249) and CSIC for supporting a research stay at IMR Bergen, and the University of Girona for the
PhD funding program (BR-UdG 2015). Likewise, C.G.-F. would like to thank the Fundación Tatiana Pérez de
Guzmán el Bueno for financial support towards her PhD, Peer reviewed

7 pages, 2 tables, 3 figures, Despite its economic importance, the population structure of the European hake, Merluccius merluccius, is unresolved, and the species is assessed based on two stocks (northern and southern) separated by the Capbreton Canyon. In order to shed light into the European hake population structure, we used Restriction-site-Associated DNA sequencing (RAD-seq) to discover and genotype thousands of genome-wide single nucleotide polymorphisms in more than a hundred samples. Our population genetic inferences confirm differentiation of Mediterranean and northeast Atlantic locations and reveal management relevant information within the latter. First, hake in the Norwegian Sea is genetically different from that of the rest of the locations under study and, second, samples from the eastern Bay of Biscay and the northwestern Iberian Peninsula are not genetically different. These results imply that samples from the northern stock belong to different genetic populations, and that samples belonging to locations included in the northern and southern stocks are part of a single genetically homogeneous population. Although the definition of the boundary between the northern and southern stocks and the potential need for additional stocks still requires further analyses, the mismatch between biological and management units should already be considered in further assessments of European hake, This work was supported by the Spanish Ministry of Economy and Competitiveness (grant CTM2015-66676), and by the Department of Agriculture and Fisheries of the Basque and Government (grant GENPES), Peer reviewed

Increasing sea temperature is a driver of change for many fish traits, particularly for fast-growing epipelagic species with short life spans. With warming, altered spawning phenology and faster growth may produce substantially larger body sizes of the new cohort, affecting fishery productivity. We present an individual-based model (IBM) that predicts the distribution of fish length at catch under observed and projected thermal scenarios, accounting for mortality, temperature-dependent spawning phenology, temperature- and photoperiod- dependent growth. This IBM was demonstrated with Coryphaena hippurus (common dolphinfish), a circumglobally-distributed and highly thermophilic species sustaining commercial and recreational fisheries where it is present. The model projected a 13.2% increase in the average length at catch under marine heatwave conditions compared to the current thermal regime (1995–2005 average). Projections under RCP scenarios 4.5 and 8.5 by the end of the century led to 5.1% and 12.8% increase in average length, respectively. Furthermore, these thermal scenarios affected spawning phenology differently, producing higher variance in body size under RCP 8.5 scenario with respect to marine heatwave conditions. This study highlights how the environmental effects of climate change can alter the distribution of species length at catch., The present paper is part of the CERES project (H2020, EU 678193). Part of the data was obtained from the FAO-Copemed and FAO-Copemed II projects (http://www.faocopemed.org/). This study has been conducted using E.U. Copernicus Marine Service Information. V. Moltó acknowledges a predoctoral grant funded by the Regional Government of the Balearic Islands and the European Social Fund, A. Ospina Álvarez was supported by H2020 Marie Skłodowska-Curie Actions (746361), and S. Pérez-Mayol salary was founded by PN Project DREAMER (CTM2015-66676-C2-1-R). We also acknowledge Andreina Fenech, Marie Louise Pace, and Roberta Mifsud from the Department of Fisheries and Aquaculture of Malta for the data collection and provision., Peer reviewed

14 pages, 5 figures, 2 tables.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY), The European hake (Merluccius merluccius) is represented as one of the most valuable fisheries in the Galician shelf. We analyzed the distribution, abundance, and environmental conditions of the southern-stock European hake larvae from the Galician shelf during the two main spawning peaks, winter-spring and summer, based on the data from three ichthyoplankton surveys (March 2012, March 2017, and June 2017). A total of 395 larvae in March 2012, 121 in March 2017, and 69 in June 2017 were captured. The northeast section of the study area, close to Estaca de Bares, primarily between 100 and 200 m isobaths, had the highest presence of the European hake larvae in all surveys. Generalized additive models (GAMs) indicated that the occurrence of larvae was significantly different between the surveys and was associated negatively with the temperature, while the abundance of larvae was significantly different between sampling years and was the highest at a temperature around 13.36°C and at sea surface heights of about −0.48 m. Studies of the distribution of early life stages and their relation to external conditions are essential to the understanding of the complex process of recruitment, especially in the exploited species and in highly dynamic environments like the Galician shelf, This study was carried out with financial support from the CRAMER (CTM2010-21856-218567-CO3-02) and DREAMER projects (CTM2015-66676-C2-1-R) funded by the Spanish National Research Program. CG-F was supported by a Predoctoral Fellowship from the Fundación Tatiana Pérez de Guzmán el Bueno, as well as the support by Do*Mar (Ph.D. program). JJS was supported by the National Science Foundation Graduate Research Fellowship. JKL was supported by the Academic Programs Office at Woods Hole Oceanographic Institution, Peer reviewed

333 pages, [EN] Fishing is an essential activity worldwide not only as a source of food but also as an economic livelihood. Currently, overfishing is a major problem in exploited stocks which triggers significant changes in the stock structure of many fish populations. This situation does not allow to maintain in a long-term a sustainable harvest. Hence, it is essential to regulate extraction of fishery resources to not to jeopardise the sustainability of fish stocks. Stock assessment use models to forecast the production capacity of a stock and predict its future in order to control fishing. One of the cornerstone of this assessment is the S-R relationship, i.e., the relation of the adult biomass (S) and the recruits (R), understanding by recruitment the number of individuals reaching a certain age, once the massive mortality of the early stages has been exceeded. Based on the spawning stock biomass (SSB), the annual recruitment is estimated and reference points for fisheries stock management are extracted from this relationship. However, it has been observed in several exploited stocks an uncoupling in the S-R relationship which hampers the assessment. One reason can be that these models assume an equal production by each individual in the population, without considering parental effects on stock reproductive potential (SRP). SRP is the ability of females to produce viable offspring that reach recruitment age. Egg production is affected by several internal (e.g., female size or condition) and external factors (e.g. food availability and environmental conditions) which modulate the spawning dynamics and productivity, [ES] La pesca es una actividad esencial en todo el mundo, no sólo por proporcionar una fuente de alimento de alta calidad nutricional sino también por ser motor económico y medio de vida en muchas regiones del planeta. En la actualidad, muchas de las poblaciones de peces sufren una presión pesquera elevada, lo que, en ocasiones, deriva en una sobreexplotación del recurso. Esta sobrexplotación provoca cambios en la estructura poblacional y puede producir el colapso del stock, impidiendo una explotación sostenible. Por ello, es fundamental regular la extracción de los recursos pesqueros utilizando el mejor conocimiento científico y socio-económico disponible. La evaluación pesquera utiliza modelos para predecir la capacidad de producción de una población y pronosticar su futuro a fin de controlar por medio de la gestión pesquera la actividad extractiva. Uno de los aspectos clave en esta evaluación es la relación S-R, es decir, la relación de la biomasa adulta (S) y los reclutas (R), entendiendo por reclutamiento el número de individuos que alcanzan una determinada edad, una vez superada las primeras etapas de mortalidad masiva. A partir de la biomasa de la población reproductora, se estima el reclutamiento anual y de la relación S-R se extraen los puntos de referencia biológicos que son usados en gestión pesquera. Sin embargo, se ha observado en muchas poblaciones explotadas un desacoplamiento en la relación S-R que dificulta la evaluación. Uno de los motivos es la asunción que hacen este tipo de modelos de una producción equivalente por parte de cada individuo de la población, sin tener en cuenta los efectos parentales sobre el potencial reproductivo de la población (PR). El PR se define como capacidad que tiene una población para producir descendencia viable que alcance la edad de reclutamiento y depende de diversos factores internos (por ejemplo, el tamaño o la condición de la hembra) y externos (por ejemplo, la disponibilidad de alimento y las condiciones ambientales) que modulan la dinámica de desove y la productividad, La presente tesis ha sido posible gracias a la Beca predoctoral en Medioambiente concedida por la Fundación Tatiana Pérez de Guzmán el Bueno en el año 2017. Además, a los proyectos de la Agencia Española de Investigación: Ecología del reclutamiento de la merluza: implicaciones sobre la gestión del recurso (CTM2010-21856-C03-00) y Dinámica del reclutamiento de la Merluza Europea (CTM2015-66676-C2), No

13 pages, 5 figures, 4 tables.-- This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license, Daily growth patterns and their relationship with reproduction was analyzed in the European hake from the Galician Shelf, where it shows a very protracted spawning with three spawning peaks. The daily growth analysis was performed in otoliths of adult females on the transversal section of the sagittae otolith. Daily increments were measured from the border to the nucleus in females until they were discernible. Results show that daily growth of females decreases during the spawning period because they allocate less energy to somatic growth in favor of the production of gametes, with an increase in growth in July. Lastly, daily growth individual trends showed a “spawning pattern” in 28% of medium and large females, suggesting an individual spawning period of one to two months, with 4–5 valleys of narrow daily increments, likely associated to batch release: individual spawning frequency would be 4–5 days. This is the first time that individual spawning frequency in hake is estimated based on individual data. Finally, the spawning pattern is detected only once per year, indicating that a single female participates only in one spawning peak per year, supporting the hypothesis of the existence of two or more spawning components in the stock, C.G.-F. was funded by Predoctoral Fellowship from the Fundación Tatiana Pérez de Guzmán el Bueno and the study was carried out with financial support from the DREAMER project (CTM2015-66676-C2-1-R) funded by the Spanish National Research Program, Peer reviewed

15 pages, 6 figures, 3 tables, European hake is an economically important fishery resource with known declines in population abundances and biomass in the last decades. However, little is known about the effect of these abundance declines on the genetic diversity levels of the stocks. In this study, we analysed genomic data of Atlantic and Mediterranean European hake populations, representing the main fishery stocks. The results indicate that abundance declines have likely affected the levels and patterns of genetic diversity within and among the three analysed populations. The Mediterranean population shows lower genetic diversity than the Atlantic ones and can be slightly genetically differentiated from them. Results indicate significant deviations from neutral expectations for constant population sizes, and substantial population declines in all three populations. Estimates of recent and ancestral effective population size (Ne) obtained from coalescence, linkage disequilibrium and sibship methods were coherent with each other. Historical Ne estimates suggest drastic declines of more than 90% in all three populations within the last 15 generations (i.e. nearly 50 years). Positive correlations observed between historical Ne and stock parameters indicative of abundances support the historical trends of estimated Ne. Since genetic variation is essential for populations facing anthropogenically induced environmental changes, this study demonstrates the importance of population genetic estimates for planning management strategies targeting the long-term sustainability of European hake fisheries, NPM was supported by MSCA-PF 101066785 (FISHADAPT https://doi.org/10.3030/101066785). This study was framed within the Marine Science Programme (ThinkInAzul) supported by the Ministerio de Ciencia e Innovación and Xunta de Galicia with funding from the European Union NextGenerationEU (PRTR-C17.I1) and European Maritime and Fisheries Fund. IGC was funded by the Spanish Ministry of Universities (Margarita Salas postdoctoral fellowship, ref. RSU.UDC.MS17). DREAMER-1 was funded by the Spanish National R + D project “Dynamics of European hake recruitment” (CTM2015-66676-C2-1-R). The North Sea IBTS-Q3 and MEDITS surveys are co-funded by the European Union through the European Maritime and Fisheries Fund (EMFF) within the national program of collection, management, and use of data in the fisheries sector and support for scientific advice regarding the Common Fisheries Policy. This manuscript is built on scientific data and information collected under Service Contract “Improving cost-efficiency of fisheries research surveys and fish stocks assessments using next-generation genetic sequencing methods [EMFF/2018/015]” (EU Contract—EASME/EMFF/2017/1.3.2.10/SI2.790889) signed with the European Climate, Infrastructure and Environment Executive Agency (CINEA) and funded by the European Union, Peer reviewed