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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Mounting evidence now shows that fishing activity modifies both heritable lifehistory traits and ecological processes in harvested populations. However, ecological and evolutionary changes are intimately linked and can occur on the same time scale, and few studies have investigated their combined effect on fish population dynamics. Here, we contrast two population subunits of a harvested fish species in the Northeast Atlantic, the European hake (Merluccius merluccius), in the light of the emerging field of evolutionary demography, which considers the interacting processes between ecology and evolution. The two subunits experienced similar age/size truncation due to size-selective fishing, but displayed differences in key ecological processes (recruitment success) and phenotypic characteristics (maturation schedule). We investigate how temporal variation in maturation and recruitment success interactively shape the population dynamics of the two subunits. We document that the two subunits of European hake displayed different responses to fishing in maturation schedules, possibly because of the different level of adaptive phenotypic plasticity. Our results also suggest that high phenotypic plasticity can dampen the effects of fisheries-induced demographic truncation on population dynamics, whereas a population subunit characterized by low phenotypic plasticity may suffer from additive effects of ecological and life-history responses. Similar fishing pressure may thus trigger contrasting interactions between life history variation and ecological processes within the same population. The presented findings improve our understanding of how fishing impacts ecoevolutionary dynamics, which is a keystone for a more comprehensive management of harvested species. [ABSTRACT FROM AUTHOR]

Fisheries ecologists traditionally aimed at disentangling climate and fishing effects from the population dynamics of exploited marine fish stocks. However, recent studies have shown that internal characteristics and external forcing (climate and exploitation) have interactive rather than additive effects. Thought most of these studies explored how demographic truncation induced by exploitation affected the response of recruitment to climate, identifying a general pattern revealed to be difficult as interactions are often case-specific. Here we compared five exploited stocks of European hake Merluccius merluccius from the Atlantic Ocean and Mediterranean Sea to investigate how the interaction between internal characteristics and external forces affect the variability of the population growth rate and their consequences on recruitment. Our results show that demographic truncation induces a novel population scenario in which the growth rate is maximized when the reproductive stock is younger and less diverse. This scenario is shaped by the climate variability and the fishing pattern. The population growth rate becomes more dependent on the maturation schedule and less on the survival rates. The consequences for the recruitment dynamics are twofold; the effect of density-dependent regulatory processes decreases while the effect of the density-independent drivers increases. Our study shows that the interaction between internal characteristics and external forces changes across geographic locations according to 1) the importance of demographic truncation, 2) the influence of the climate on the regional hydrography and 3) the spatiotemporal heterogeneity of the physical environment to which fish life history is adapted. [ABSTRACT FROM AUTHOR]

Abstract: Stock recruitment (SR) relationships aim to predict the recruitment based on a given level of reproductive stock. Though the spawning stock biomass (SSB) is commonly used to fit such SR models, there is increasing evidence that the total egg production (TEP) is a more relevant stock reproductive potential index. Indeed, the TEP takes into account both the size-dependent capacity of females to produce eggs and the demographical structure of the spawning stock. This paper presents a method to assess the TEP based on the fecundity and egg quality based on the age as well as spawning fraction for the southern stock of European hake (Merluccius merluccius). The fecundity and egg quality increased significantly as the female size increased. The spawning fraction also increased with female size. Larger females concentrated their reproductive period during the first quarter of the year, whereas smaller ones spawned throughout the year. The stock''s demographic structure showed a clear increase in the proportion of younger females and a reduction of older ones through the 1982–2007 time-series, which led to a decrease of egg production per unit of female SSB. Our results showed a significant contribution of older individuals to the reproductive output. The relevance of using TEP as an index of stock reproductive potential is discussed. [Copyright &y& Elsevier]