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Long-term ecological surveys (LTES) often exhibit strong variability among sampling dates. The use and interpretation of such interannual variability is challenging due to the combination of multiple processes involved and sampling uncertainty. Here, we analysed the interannual variability in ~30 years of 150 species density (fish and invertebrate) and environmental observation time series in four aquatic systems (stream, river, estuary, and marine continental shelf) with different sampling efforts to identify the information provided by this variability. We tested, using two empirical methods, whether we could observe simultaneous fluctuation between detrended time series corresponding to widely acknowledged assumptions about aquatic population dynamics: spatial effects, cohort effects, and environmental effects. We found a low number of significant results (36%, 9%, and 0% for spatial, cohort, and environmental effects, respectively), suggesting that sampling uncertainty overrode the effects of biological processes. Our study does not question the relevance of LTES for detecting important trends, but clearly indicates that the statistical power to interpret interannual variations in aquatic species densities is low, especially in large systems where the degree of sampling effort is always limited. Les etudes ecologiques a long terme (<>) font souvent ressortir une forte variabilite entre les dates d'echantillonnage. Il est difficile d'utiliser et d'interpreter cette variabilite en raison de la combinaison de differents processus impliques et de l'incertitude associee a l'echantillonnage. Nous analysons la variabilite interannuelle sur environ 30 ans de 150 series temporelles de densite specifique (poissons et invertebres) et d'observations environnementales dans quatre systemes aquatiques (ruisseau, fleuve, estuaire et plateau continental marin), caracterisees par differents efforts d'echantillonnage, afin d'identifier l'information que fournit cette variabilite. Nous verifions, en utilisant deux methodes empiriques, s'il est possible d'observer des fluctuations simultanees des series temporelles detendancees correspondant a des hypotheses largement reconnues concernant la dynamique de populations aquatiques, a savoir : les effets spatiaux, les effets de cohorte et les effets environnementaux. Nous relevons un petit nombre de resultats significatifs (36 %, 9 % et 0 % pour les effets spatiaux, de cohorte et environnementaux, respectivement), ce qui donne a penser que l'incertitude associee a l'echantillonnage masque les effets de processus biologiques. L'etude ne remet pas en question la pertinence des LTES pour ce qui est de faire ressortir des tendances importances, mais elle indique clairement que la puissance statistique associee a l'interpretation des variations interannuelles de la densite d'especes aquatiques est faible, particulierement pour les grands systemes pour lesquels l'effort d'echantillonnage est toujours limite. [Traduit par la Redaction], Introduction Long-term ecological surveys (LTES) are essential to examine the dynamics of ecosystems and identify the processes involved (Hobbie et al. 2003; Magurran et al. 2010; Kuebbing et al. 2018). [...]

Studying demographic and genetic connectivity can help assess marine metapopulation structure. Rays and skates have no larval phase; hence, population connectivity can only result from active movement of individuals. Using thornback ray (Raja clavata) in European waters as a case study, demographic and genetic connectivity were studied for 11 putative populations with unequal population abundances and two hypotheses of dispersal rates. Genetic simulation results highlighted three large metapopulations: in the Mediterranean, around the Azores, and on the Northeast Atlantic shelf. Demographic results highlighted a finer population structure indicating that several pairs of putative populations might be demographically linked. Results were highly sensitive to dispersal assumptions and relative population abundances, which provided insights into the potential magnitude of genetic and demographic connectivity differences. Accounting for demographic connectivity appears to be crucial for managing and conserving rays and skates, while genetic connectivity provides a longer-term perspective and less subtle spatial structures. Moreover, accounting for heterogeneity in population abundances is a key factor for determining or interpreting metapopulation connectivity. L'etude de la connectivite demographique et genetique peut aider a evaluer la structure des metapopulations marines. Les raies n'ont pas de stade larvaire, de sorte que la connectivite des populations ne peut decouler que de deplacements actifs d'individus. Utilisant le cas de la raie bouclee (Raja clavata) dans les eaux europeennes, nous avons etudie la connectivite demographique et genetique pour 11 populations presumees en simulant des abondances inegales des populations ainsi que deux hypotheses de dispersion. Les resultats des simulations genetiques font ressortir trois grandes metapopulations, une dans la Mediterranee, une autour des Azores et une sur le plateau continental de l'Atlantique nord-est. Les resultats demographiques font ressortir une structure de populations plus fine qui indique que plusieurs paires de populations presumees pourraient etre reliees du point de vue demographique. Les resultats sont tres sensibles aux hypotheses concernant la dispersion et aux abondances relatives des populations, ce qui fournit de l'information sur l'ampleur possible des differences de connectivite genetique et demographique. La prise en consideration de la connectivite demographique semble revetir une importance cle pour la gestion et la conservation des raies, alors que la connectivite genetique fournit une perspective a plus long terme et des structures spatiales moins fines. La prise en consideration de l'heterogeneite de l'abondance des populations constitue en outre un facteur cle pour determiner ou interpreter la connectivite de metapopulations. [Traduit par la Redaction], Introduction Population connectivity is a crucial parameter to take into account when defining population units relevant for management and conservation purposes (Stearns and Hoekstra 2005; Sinclair et al. 2006; Schwartz [...]

Information on stock identification and spatial stock structure provide a basis for understanding fish population dynamics and improving fisheries management. In this study, otolith shape analysis was used to study the stock structure of blue whiting (Micromesistius poutassou) in the northeast Atlantic using 1693 samples from mature fish collected between 37°N and75°N and 20°W and 25°E. The results indicated two stocks located north and south of ICES Divisions Via and VIb (54°5N to 60°5N, 4°W to 11°W). The central area corresponds to the spawning area west of Scotland. Sampling year effects and misclassification in the linear discriminant analysis suggested exchanges between the northern and southern stocks. The results corroborate previous studies indicating a structuring of the blue whiting stock into two stocks, with some degree of mixing in the central overlap area. L'identification et la connaissance de la structuration spatiale de stocks sont essentielles pour etudier la dynamique des populations de poissons et ainsi gerer les pecheries. Dans cette etude, la forme des otolithes a ete employee pour comprendre la structuration des stocks des merlans bleus (Micromesistius poutassou) dans le nord-est de l'Ocean Atlantique a partir de 1693 poissons matures echantillonnes entre 37°N-75°N et 20°O-25°E. Les resultats indiquent la presence de deux stocks situes au nord et au sud, respectivement, des divisions VIa et VIb du CIEM (de 54°5N a 60°5N, de 4°O a 11°O). La zone centrale correspond a la zone de frai a l'ouest de l'Ecosse. Les effets du facteur annee d'echantillonnage et la mauvaise classification dans l'analyse lineaire discriminante suggere des echanges entre les composants nordique etmeridionale. Ces resultats corroborent des etudes anterieures indiquant une structuration des merlans bleus en deux stocks avec un certain niveau de melange dans la zone de chevauchement., Introduction Stock identification and information on spatial structure provide a basis for understanding population dynamics and in turn to improve fisheries management. Several techniques can be used for stock identification, [...]

Sustainable exploitation of marine populations is a challenging task relying on information about their current and past abundance. Fisheries‐related data can be scarce and unreliable making them unsuitable for quantitative modelling. One fishery independent method that has attracted attention in this context consists in estimating the effective population size (Ne), a concept founded in population genetics. We reviewed recent empirical studies on Ne and carried out a simulation study to evaluate the feasibility of estimating Ne in large fish populations with the currently available methods. The detailed review of 26 studies found that published empirical Ne values were very similar despite differences in species and total population sizes (N). Genetic simulations for an age‐structured fish population were carried out for a range of population and samples sizes, and Ne was estimated using the Linkage Disequilibrium method. The results showed that already for medium‐sized populations (1 million individuals) and common sample sizes (50 individuals), negative estimates were likely to occur which for real applications is commonly interpreted as indicating very large (infinite) Ne. Moreover, on average, Ne estimates were negatively biased. The simulations further indicated that around 1% of the total number of individuals might have to be sampled to ensure sufficiently precise estimates of Ne. For large marine populations, this implies rather large samples (several thousands to millions of individuals). If however such large samples were to be collected, many more population parameters than only Ne could be estimated. [ABSTRACT FROM AUTHOR]

In this paper, I argue that we have at hand what is needed to provide scientific advice for ecosystem-based management of small pelagics and other species groups now. The ingredients for this advice are (i) large marine ecosystems as spatial management units; (ii) maintaining ecosystem productivity and exploiting at multispecies maximum yield as overarching management objectives; (iii) assessment of ecosystems by evaluating changes in primary productivity; (iv) an operational management procedure in which single-species catch proposals are adjusted to ecosystem productivity using a set of control rules. Inspection of historic landings for small pelagics and other small species in the Northeast Atlantic (ICES area) reveals that most likely fisheries exploitation does not, and never did, exceed system productivity in most LMEs and is therefore overall sustainable, although not necessarily for individual stocks. [ABSTRACT FROM AUTHOR]

Zebrafish were exposed through diet to two environmentally relevant polycyclic aromatic hydrocarbons (PAHs) mixtures of contrasted compositions, one of pyrolytic (PY) origin and one from light crude oil (LO). Monoamine concentrations were quantified in the brains of the fish after six month of exposure. A significant decrease in noradrenaline (NA) was observed in fish exposed to both mixtures, while a decrease in serotonin (5HT) and dopamine (DA) was observed only in LO-exposed fish. A decrease in metabolites of 5HT and DA was observed in fish exposed to both mixtures. Several behavioural disruptions were observed that depended on mixtures, and parallels were made with changes in monoamine concentrations. Indeed, we observed an increase in anxiety in fish exposed to both mixtures, which could be related to the decrease in 5HT and/or NA, while disruptions of daily activity rhythms were observed in LO fish, which could be related to the decrease in DA. Taken together, these results showed that (i) chronic exposures to PAHs mixtures disrupted brain monoamine contents, which could underlie behavioural disruptions, and that (ii) the biological responses depended on mixture compositions. [ABSTRACT FROM AUTHOR]

We present a framework for evaluating fisheries management plans comprehensively, both rebuilding plans and others. The framework includes a first rapid appraisal of the likelihood that the plan will result in management meeting its objectives, and guides subsequent quantitative analyses of potential weaknesses in the proposed plan. The framework includes four steps: (i) evaluating if a set of management objectives, if achieved, would result in a sustainable fishery, (ii) using qualitative analysis of a bio-economic model to evaluate whether the set of stock management tactics might be capable of achieving the specified fisheries objectives, (iii) using empirical criteria derived from the literature to evaluate if other management measures in the plan related to the ecological, social or economic context of the fishery actually contribute to sustainability, and (iv) carrying out quantitative simulations to compare alternative implementation options. Generally, several management measures have to be combined to increase stock size without sacrificing the economic benefits to the fishers remaining in the fishery. We demonstrate application of the framework for evaluating the stock rebuilding plan for plaice ( Pleuronectes platessa) and sole ( Solea solea) in the North Sea and, the management measures currently in place for the roundnose grenadier ( Coryphaenoides rupestris) stock exploited to the west of the British Isles. [ABSTRACT FROM AUTHOR]