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Many anguillid eel species display facultative catadromy. Some eel spend their entire life cycle in marine coastal areas, but the geographical extent of this, especially at the extremes of their distributional ranges, is unknown. We analysed otolith Sr:Ca and Ba:Ca from yellow-stage European eel (Anguilla anguilla) sampled along the coast of Norway and in several freshwater lakes (58[degrees]N-63[degrees]N), to infer their initial settlement and later life movement patterns with regards to habitat salinity. Most eel (80%) sampled in marine habitats (n = 371) had settled and remained in marine water, but 20% had moved between marine and freshwater habitats and were hence classified as inter-habitat shifters. Among freshwater sampled eel (n = 99), 80% had settled and remained in fresh water, but 20% were classified as inter-habitat shifters. The average growth rates for marine water residents, inter-habitat shifters, and freshwater residents were 35, 27, and 17 mm * [year.sup.-1], respectively. Northern European shallow marine habitats may serve as important yellow eel growth habitats and may be critical to buffer the European eel population against the general decrease in continental recruitment. Key words: otolith microchemistry, anguillids, Anguilla anguilla, salinity, age, growth rate, 1. Introduction The decline of the panmictic European eel (Anguilla anguilla) population is well documented (Drouineau et al. 2018; ICES 2020). The data used to support this apparent decline have [...]

We combined fatty acid (FA) and stable isotope (SI) analyses to investigate the trophic ecology of different stages of European eels (Anguilla anguilla) across seawater (SW), brackish water (BW), and freshwater (FW) habitats. Salinity was the main driver of differences in the biochemical composition, and the greatest variation occurred between SW and FW eels. SW eels had a higher content of the FA indicator of carnivory, as well as the highest stable isotope ratios (C, N). In contrast, FW eels exhibited the highest lipid content and omega-6 polyunsaturated FA, but the lowest stable isotope ratios, suggesting major dietary differences between the eels in these two habitats. While the biochemical composition of BW eels was closer to those of SW eels, BW eels had the largest SI range, indicating higher dietary plasticity. FW individuals had better overall condition compared to SW eels. Independent of habitat, larger individuals were in the best condition, and had higher lipid content and monounsaturated FA. These findings suggest a biological advantage for eels to maintain a catadromous life history strategy. Nous avons combine des analyses d'acides gras (AG) et d'isotopes stables (IS) afin d'etudier l'ecologie trophique d'anguilles europeennes (Anguilla anguilla) a differentes etapes de leur cycle biologique dans des habitats d'eau de mer (EM), d'eau saumatre (ES) et d'eau douce (ED). La salinite s'avere la principale cause des variations de composition biochimique, et les plus grandes differences sont observees entre les anguilles d'EM et d'ED. Les anguilles d'EM presentent une plus grande concentration de l'AG indicateur de la carnivorie, ainsi que les rapports d'isotopes stables (C, N) les plus eleves. En comparaison, les anguilles d'ED presentent la plus forte teneur en lipides et en AG polyinsature omega-6, mais les rapports d'isotopes stables les plus faibles, ce qui indiquerait des differences majeures des regimes alimentaires des anguilles vivant dans ces deux habitats. Si la composition biochimique des anguilles d'ES est plus proche de celle des anguilles d'EM, les anguilles d'ES presentent la plus grande fourchette d'IS, ce qui indique une plus grande plasticite de leur regime alimentaire. Les specimens d'ED presentent un meilleur embonpoint global que les anguilles d'EM. Independamment de l'habitat, les specimens plus grands presentent le meilleur embonpoint et ont les plus hautes teneurs en lipides et en AG monoinsatures. Ces constatations donnent a penser que le maintien d'une strategie de cycle biologique catadrome offre un avantage biologique aux anguilles. [Traduit par la Redaction], Introduction The European eel (Anguilla anguilla) is a facultatively catadromous species (Tzeng et al. 2000; Daverat et al. 2006). Adult eels reproduce and spawn in the Sargasso Sea. From there, [...]

Understanding the trophic ecology of deep-sea communities provides valuable insight into deep-water ecosystem functioning, and can help inform fisheries management and conservation initiatives. However, few deep-sea food webs have been studied so far in the Northwest Atlantic. Here, stable isotope, gut content, and morphometric analyses were combined to explore trophic relationships in a deep-water fish assemblage off eastern Canada. While a weak depth effect was found on the isotopic composition of the species analyzed, isotopic and dietary records revealed the existence of two main, strongly coupled trophic pathways. The pelagic pathway either comprised pelagic fishes (e.g., meso- and bathypelagic species), primarily feeding on zooplankton and fish, or benthopelagic predators that showed a more pelagic-oriented diet. Such fishes displayed the lowest values of stable N and C isotope ratios. In contrast, demersal fishes representing the benthic trophic pathway had significantly higher values of [delta].sup.15N and [delta].sup.13C, and a taxonomically more benthic-oriented and diverse diet. Furthermore, smaller body sizes, larger mouths, and adaptations (e.g., bioluminescent structures and lures) prevailed in the pelagic species, consistent with living in a relatively food-poor environment. The largest average body sizes were found in the demersal fishes suggesting enhanced food intake and growth investment for the species. Only juvenile individuals of threatened species, such as Coryphaenoides rupestris and Rajella fyllae were caught, providing evidence of the vulnerability of such species to commercial fishing., Author(s): Camilla Parzanini [sup.1] , Christopher C. Parrish [sup.1] , Jean-François Hamel [sup.2] , Annie Mercier [sup.1] Author Affiliations: (1) Department of Ocean Sciences, Memorial University, 0000 0000 9130 6822, [...]

Fatty acids in neutral and polar lipids were used to investigate trophic connections in species from five families of demersal (Rajella fyllae , Malacoraja senta , Alepocephalus bairdii , Borostomias antarcticus) and pelagic fish (Bathytroctes macrolepis , Lampanyctus spp. Chaulidos sloani , Serrivomer beanii) sampled in the deep Atlantic Ocean off Newfoundland, Canada. Lipid extracts were fractionated into neutral, acetone-mobile polar, and phospholipids to separate fatty acids in storage from those in membranes. Multivariate analysis of fatty acids showed that there were greater differences among the three lipid fractions than there were among the species when all fatty acid fractions were considered together. Neutral lipid fatty acids were characterized by monoenes, acetone-mobile polar lipids (AMPL) by C18 polyenes, and phospholipids by 16:0 and DHA. Multivariate analysis of fatty acids in phospholipids showed a strong grouping by taxonomic family (>80% similarity), while the neutral lipid fatty acids showed a weaker grouping by family (72.5% similarity) but groupings that also related to habitat and vertical migration. The neutral lipid data supported the use of 20:1ω9 as a biomarker of calanoid copepods and of 16:1ω7 as a marker of diatoms to determine food web connections in deep-sea fish, but not some other common markers. In addition, correlations with δ15N showed that series of ω6 and ω7 fatty acids were trophically transferred though neutral lipids, especially the essential fatty acid, ARA. Neutral lipids were also reservoirs for essential ω3 fatty acids in demersal species, but the major reservoir for DHA was AMPL and phospholipid in pelagic species. [ABSTRACT FROM AUTHOR]

Biochemical markers developed initially for food-web studies of terrestrial and shallow-water environments have only recently been applied to deep-sea ecosystems (i.e. in the early 2000s). For the first time since their implementation, this review took a close look at the existing literature in the field of deep-sea trophic ecology to synthesize current knowledge. Furthermore, it provided an opportunity for a preliminary analysis of global geographic (i.e. latitudinal, along a depth gradient) trends in the isotopic (δ15N, δ13C) and fatty acid composition of deep-sea taxa. Results revealed significant relationships along the latitudinal and bathymetric gradients. Deep-sea animals sampled at temperate and polar latitudes displayed lower isotopic ratios and greater proportions of essential ω3 long-chain polyunsaturated fatty acids (LC-PUFA) than did tropical counterparts. Furthermore, δ15N and δ13C ratios as well as proportions of arachidonic acid increased with increasing depth. Since similar latitudinal trends in the isotopic and fatty acid composition were found in surface water phytoplankton and particulate organic matter, these results highlight the link across latitudes between surface primary production and deep-water communities. Because global climate change may affect quantity and quality (e.g. levels of essential ω3 PUFA) of surface primary productivity, and by extension those of its downward flux, the dietary intake of deep-sea organisms may likely be altered. In addition, because essential ω3 PUFA play a major role in the response to temperature variations, climate change may interfere with the ability of deep-sea species to cope with potential temperature shifts. Importantly, methodological disparities were highlighted that prevented in-depth analyses, indicating that further studies should be conducted using standardized methods in order to generate more reliable global predictions. [ABSTRACT FROM AUTHOR]