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Arctic cod (Boreogadus saida) is a schooling fish providing a critical link between lower and upper trophic levels in the Arctic. This study examined foraging of Arctic cod collected from Allen Bay, Cornwallis Island, Canada (~75 N 95 W), during summer 2010 using temporal indicators of diet including stomach content, and carbon ([delta][sup.13]C) and nitrogen ([delta][sup.15]N) stable isotopes of liver and muscle. Foraging at the time of capture reflected sympagic and epi-benthic habitats indicated by the prevalence of cyclopoid and harpacticoid copepods in stomachs, whereas stable isotope data, which provide an estimate of feeding over a longer period, indicated pelagic prey as important. Prey selection of juveniles differed from adults based on stable isotopes, while large adults showed the most separation based on stomach contents, suggesting size-related diet shifts. Compared to studies near Resolute in the 1970s, 1980s, and 1990s, growth and pre-spawning gonadal conditions of Arctic cod have not changed., Introduction Arctic cod (Boreogadus saida) is a critical link structuring energetic pathways in marine ecosystems throughout the Arctic (Bain and Sekerak 1978; Welch et al. 1992). Understanding its role in [...]

The Greenland shark (Somniosus microcephalus) is the only shark species known to inhabit ice-covered seas in the North Atlantic, but remains a missing component in most studies of Arctic food webs. In the present study, stable isotopes (SIs) of nitrogen (δ[sup.15]N) and carbon (δ[sup.13]C) and fatty acids (FAs) were analyzed to identify the role of Greenland sharks (sampled during June 2008-2009) in Kongsfjorden, a productive fjord on the west coast of Svalbard, Norway (*79°N, 12-13°E). The Greenland shark fed at a high trophic position (4.8) based on δ[sup.15]N values, and δ[sup.13]C confirmed that most (70 %) of their carbon was derived from phytoplankton-based food chains, which is consistent with a heavy reliance on pelagic teleosts and seals. Greenland sharks from Kongsfjorden had fatty acid profiles in both muscle and plasma (e.g., low 20:1n-9, high 22:5n-) that suggested a low portion of Greenland halibut (Reinhardtius hippoglossoides) and high proportion of gadoids and seals in their diet compared to Greenland sharks sampled in Cumberland Sound, Canada, during April 2008, which were previously shown to derive much of their energy from Greenland halibut. The high proportions of seal fatty acids in both slow- (muscle) and fast- (plasma) turnover tissues indicate that trophic interactions between Greenland sharks and seals in Kongsfjorden are a common occurrence. Results from the present study suggest that Greenland sharks likely play a unique and significant role in Arctic marine food webs as a top predator of fishes and marine mammals., Introduction Sharks play important and unique roles in marine ecosystems (Ferretti et al. 2010) and tend to be highly connected in food webs (i.e., involved in many trophic interactions) because [...]

Our results provide new information that diet, carbon source and trophic position of an invasive fish species, round goby (Neogobius melanostomus), varies seasonally, spatially and with body size in littoral habitats of Lake Ontario. Based on stomach contents and stable isotopes, round goby fed at a higher trophic position in the cooler, less productive Kingston Basin relative to the Bay of Quinte. Bay of Quinte round goby were more reliant on terrestrial carbon, whereas littoral carbon dominated in the Kingston Basin. Although stomach contents suggested dreissenids were the dominant prey item of round goby, stable isotope mixing models estimated that dreissenids were never >39% and 11% of the diet in Bay of Quinte and Kingston Basin, respectively. Stable isotopes indicated amphipods, chironomids and cladocerans were the most important prey, and were at times common items in stomach contents, but this varied with site, season and year. Given their high abundance, the impact of round gobies on the benthic biodiversity of the Great Lakes may be more significant than indicated by stomach content analysis alone. Notre etude apporte de nouvelles donnees qui indiquent que le regime alimentaire, les sources de carbone et la position trophique de l'espece envahissante de poissons, le gobie a taches noires (Neogobius melanostomus), varient en fonction de la saison, de l'espace et de la taille corporelle dans les habitats littoraux du lac Ontario. D'apres les contenus stomacaux et les isotopes stables, les gobies a taches noires du bassin de Kingston, qui est plus frais et moins productif, se nourrissent a un niveau trophique plus eleve que ceux de la baie de Quinte. Les gobies a taches noires de la baie de Quinte sont plus dependants du carbone terrestre, alors que le carbone littoral predomine dans le bassin de Kingston. Bien que les contenus stomacaux indiquent que les dreissenides constituent les proies principales, les modeles de melange d'isotopes stables revelent que les dreissenides ne representent jamais >39 % du regime alimentaire dans la baie de Quinte et >11 % dans le bassin de Kingston. Les isotopes stables indiquent que les amphipodes, les chironomides et les cladoceres constituent les proies predominantes et qu'ils sont, a certains moments, frequents dans les contenus stomacaux, mais qu'il y a une variation en fonction du site, de la saison et de l'annee. Etant donne leur forte abondance, l'impact des gobies a taches noires sur la biodiversite des Grands Lacs peut etre plus important que ne l'indiquent les seuls contenus stomacaux. [Traduit par la Redaction], Introduction Quantifying spatial and temporal variability in food web structure and fish diet remains a challenge for ecologists (Warren 1989; Martinez et al. 1999; McCann et al. 2005). Aquatic habitats [...]

Understanding the role of predators is challenging but critical for ecosystem management. For community dynamics, predator-specific size-based variation in diet, trophic position, and habitat use are rarely accounted for. Using two applied tools (stable isotopes and stomach content data), we examined inter- and intra-species ontogenetic variability in diet (stomach contents), trophic position ([TP.sub.SIA] for δ[sup.15]N and [TP.sub.SCA] for stomach contents), and habitat use (δ[sup.13]C) of two large sharks, the scalloped hammerhead (Sphyrna lewini) and the dusky (Carcharhinus obscurus). Stomach contents identified size-based and gender-specific shifts in diet indicating resource partitioning for and between species. Calculated TP for the two sharks varied by method, either T-Psia or [TP.sub.SCA] and with species, size, and gender, but were complicated by differing baselines and broad functional prey groups, respectively. TP increased with size for S. lewini, but was low in large C. obscurus compared with small sharks. Size-based δ[sup.13]C profiles indicated habitat partitioning by sex in S. lewini and a movement to shelf edge foraging in large C. obscurus. These results demonstrate that predators exert proportional size-based effects on multiple components of the marine system that are further complicated by species- and gender-specific strategies. Comprendre le role des predateurs represente un defi, mais c'est essentiel pour la gestion des ecosystemes. Dans les etudes de dynamique des communautes, on tient rarement compte des variations reliees a la taille et specifiques aux predateurs dans le regime alimentaire, la position trophique et l'utilisation de l'habitat. A l'aide de deux methodes, les isotopes stables et l' analyse des contenus stomacaux, nous avons examine la variabilite inter- et intraspecifique durant l'ontogenese du regime alimentaire (contenus stomacaux), de la position trophique ([TP.sub.SIA] pour δ[sup.15]N et [TP.sub.SCA] pour contenu stomacal) et de l'utilisation de l'habitat (δ[sup.13]C) chez deux grands requins, le requin-marteau halicorne (Sphyrna lewini) et le requin obscur (Carcharhinus obscurus). Les contenus stomacaux permettent d' identifier des modifications dans le regime alimentaire reliees a la taille et specifiques au sexe qui indiquent un partitionnement des ressources chez et entre les especes. Les TP calculees pour les deux requins varient d' apres la methode utilisee, soit TPsia ou [TP.sub.SCA], et aussi en fonction de l' espece, de la taille et du sexe et elles sont compliquees respectivement par des lignes de base differentes et par des groupes fonctionnels de proies distincts. La TP augmente en fonction de la taille chez S. lewini, mais elle est basse chez les grands C. obscurus par comparaison aux petits requins. Les profils de δ[sup.13]C indiquent un partitionnement de l'habitat en fonction du sexe chez S. lewini et un deplacement vers le bord de la plate-forme chez les grands C. obscurus. Ces resultats demontrent que les predateurs exercent des effets proportionnels a leur taille sur plusieurs compartiments du systeme marin, qui sont de plus compliques par des strategies specifiques a l'espece et au sexe. [Traduit par la Redaction], Introduction Body size has long been recognized to have an important influence on the structural and functional complexity of aquatic food webs (Elton 1927). As predators are typically larger than [...]

: Stable carbon ([δ.sup.13]C) and nitrogen ([δ.sup.15]N) isotopes and total mercury (Hg) were used to investigate diet and resource use among Greenland sharks (Somniosus microcephalus) and 14 teleosts inhabiting Icelandic waters. Greenland shark stomachs contained 11 of the teleosts sampled, along with other fishes and marine mammal tissues. Teleost resource use ranged from pelagic (e.g., Argentina silus) to benthic (e.g., Anarhichas lupus) based on [δ.sup.13]C, and relative trophic positions (TP, based on [δ.sup.15]N) ranged from 3.0 (Mallotus villosus) to 3.8 (e.g., Brosme brosme). Greenland shark [δ.sup.13]C indicated feeding on benthic and pelagic resources, with a high input of pelagic carbon, and [δ.sup.15]N indicated a relative TP of 4.3. Log[Hg] increased with [delata.sup.15]N (i.e., TP) from teleosts to Greenland sharks and was higher in offshore vs. inshore teleosts. Linear regressions revealed that log[Hg] was better described by both [δ.sup.15]N and [δ.sup.13]C-assigned resource use than by [δ.sup.15]N alone. Hg was useful for supporting the TPs suggested by [δ.sup.15]N, and the higher Hg in offshore fishes could help explain the high Hg of Greenland sharks. Results from this study demonstrated the potential use of Hg as a dietary tracer in marine fishes. Resume: Les isotopes stables de carbone ([δ.sup.13]) et d'azote ([δ.sup.15]) et le mercure total (Hg) nous ont servi a etudier le regime alimentaire et l'utilisation des ressources chez la laimargue atlantique (Somniosus microcephalus) et 14 teleosteens habitant les eaux islandaises. Les estomacs de laimargues atlantiques contenaient 11 des teleosteens echantillonnes, ainsi que des tissus d'autres poissons et de mammiferes marins. L'utilisation de la ressource de teleosteens comprenait des poissons de pelagiques (par ex., Argentina silus) a benthiques (par ex., Anarhichas lupus) d'apres [δ.sup.13]C et leurs positions trophiques relatives (TP, basee sur [δ.sup.15])N variaient de 3,0 (Mallotus villosus) a 3,8 (par ex., Brosme brosme). Le [δ.sup.13]C des laimargues atlantiques indique qu'elles se nourrissent de ressources benthiques et pelagiques, avec un apport eleve de carbone pelagique et leur [δ.sup.15]N indique une TP relative de 4,3. Log[Hg] augmente en fonction de [δ.sup.15]N (c'est-a-dire la TP) des teleosteens aux laimargues atlantiques et est plus eleve chez les teleosteens du large que chez ceux de la cote. Des regressions lineaires montrent que log[Hg] est mieux decrit par l'utilisation des ressources assignees a la fois par [δ.sup.15]N et [δ.sup.13]C que par [δ.sup.15]N seul. Le Hg est utile pour appuyer les TP indiquees par [δ.sup.15]N et les concentrations plus elevees de Hg dans les poissons du large pourraient aider a expliquer les fortes concentrations de Hg dans les laimargues atlantiques. Les resultats de notre etude demontrent l'utilite potentielle de Hg comme traceur alimentaire chez les poissons marins. [Traduit par la Redaction], Introduction Knowledge concerning the diet of marine fish is important for understanding energy and contaminant flow among predators and prey and for an ecosystem-based approach to fisheries management. Stable isotopes [...]

Abstract: We conducted a diet-switching experiment using freshwater ocellate river stingrays (Potamotrygon motoro) fed a novel earthworm (Eisenia foetida) diet to establish the relative contributions of growth and metabolism to [...]

Estimating metabolic rate in wild, free‐swimming fish is inherently challenging. Here, we explored using surgically implanted heart rate biologgers to estimate metabolic rate in two warmwater piscivores, bowfin Amia calva (Linneaus 1766) and largemouth bass Micropterus salmoides (Lacepède 1802). Fish were surgically implanted with heart rate loggers, allowed to recover for 24 h, exposed to a netting and air exposure challenge, and then placed into respirometry chambers so that oxygen consumption rate (ṀO2) could be measured in parallel to heart rate (fH) for a minimum of 20 h (ca. 20 estimates of ṀO2). Heart rate across the duration of the experiment (at 19°C) was significantly higher in largemouth bass (mean ± s.d., 45 ± 14 beats min−1, range 18–86) than in bowfin (27 ± 9 bpm, range 16–98). Standard metabolic rate was also higher in largemouth bass (1.06 ± 0.19 mg O2 kg−1 min−1, range 0.46–1.36) than in bowfin (0.89 ± 0.17 mg O2 kg−1 min−1, range 0.61–1.28). There were weak relationships between fH and ṀO2, with heart rate predicting 28% of the variation in oxygen consumption in bowfin and 23% in largemouth bass. The shape of the relationship differed somewhat between the two species, which is perhaps unsurprising given their profound differences in physiology and life history, illustrating the need to carry out species‐specific validations. Both species showed some potential for a role of fH in efforts to estimate field metabolic rates, although further validation experiments with a wider range of conditions (e.g., digestive states, swimming activity) would likely help improve the strength of the ṀO2–fH relationship for use in field applications. [ABSTRACT FROM AUTHOR]

The effects of biological and chemical factors on trophic transfer of persistent organic pollutants (POPs) in an Arctic marine food web was undertaken by measuring POPs and stable isotopes of nitrogen (Omega (super 15) N) in six species of zooplankton, a benthic invertebrate, Arctic cod, and other species. The results of the study are discussed and tabulated.

Analysis of the food chain of the Northwater Polynya Arctic has shown the presence of concentrations of Hexachlorocyclohexane (HCH) isomers. While biotransformation of these isomers in birds, wish and water plants appears constant with previous findings, data shows the ringed seal has the greatest difficulty metabolizing this chemical. Charts, graphs and statistical data support the article's conclusions.

Seven laboratories participated in an international interlaboratory comparison exercise to compare the quantitative methods used for measuring [C.sub.10]-[C.sub.13] polychloro-n-alkanes (PCAs). Participants were supplied with two solutions (PCA-1, PCA-70) containing PCAs of 'known' but unstated concentrations, and two real world samples (fish extracts FE1 and FE2) each consisting of a cleaned up extract (lipid-free) of a fish tissue known to contain PCAs. A well-characterized commercial formulation, PCA60, of stated concentration was also supplied and was used as the external standard for the exercise. Participants having other commercially available [C.sub.10]-[C.sub.13] PCA mixtures were encouraged to use them as external standards for the study, and the choice of the quantitative method employed was left to participants, though all were based on high-resolution gas chromatography with detection by electron capture negative ion mass spectrometry (plus electron capture detection in one case). The results of the study met with mixed success. For measurements on the PCA-1 sample, whose composition and gas chromatographic profile were quite different from the PCA60 sample, the determined concentration was 99.3 [+ or -] 19.5 ng/[micro]L (mean [+ or -] the standard deviation of the laboratory means); the true concentration of this mixture was 74 ng/[micro]L. For the PCA-70 sample, which has a composition and gas chromatographic profile similar to that of PCA-60, the result was 297 [+ or -] 132 ng/[micro]L, compared to the true concentration of 118 ng/[micro]L. It is still unclear why the larger discrepancy arises for the latter sample; this observation implies that different commercial formulations used as standards would provide quite different estimates of PCA concentrations. The interlaboratory precision for measurements on the FE1 sample (coefficient of variation (CV) of 27%) was better than that for the FE2 sample (CV of 47%). An explanation for the larger variation is that some of the quantitative procedures used in measuring PCA levels in the FE2 sample did not take into account the effects of coeluting interferences, which are observed at nominal mass spectral resolution, thus making some of the values too high.

Ref.: Can. J. Fish. Aquat. Sci. 75(5): 759-771 (2018). dx.doi.org/10.1139/cjfas-2016-0150. The original version of Fig. 4 contained an error. The correct version is presented here. The authors apologize for this [...]