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Abstract We determined concentrations of eicosapentaenoic and docosahexaenoic acids (EPA + DHA), Σ omega -3, polyunsaturated fatty acids (ΣPUFA), selenium, methylmercury, and selenium:methylmercury (Se:Hg) ratios in native and northward-redistributing sub-Arctic marine fish and invertebrates from low, mid-, and high Canadian Arctic latitudes. There was no clear latitudinal trend in nutrient or contaminant concentrations. Among species, EPA + DHA concentrations in native Arctic cod (Boreogadus saida) were similar to concentrations in sub-Arctic capelin (Mallotus villosus) and sand lance (Ammodytes spp.) (444–658 mg.100 g-1), and higher than in most other species. Concentrations of EPA + DHA were related to lipid content, but to a greater extent for higher trophic position species (R 2 = 0.83) than for species at lower trophic positions (R 2 = 0.61). Selenium concentrations were higher in sand lance (1.15 ± 0.16 μg g−1) than in all other species (0.30–0.69 μg g−1), which was significantly, but weakly, explained by more pelagic feeding in sand lance. Methylmercury concentrations were similar (and Se:Hg ratios were higher) in capelin, sand lance, and Arctic cod (0.01–0.03 μg g−1 wet weight (ww)) and lower than in other prey (0.12–0.26 μg g−1 ww), which was significantly explained by the smaller size of these species and more pelagic feeding habits than other fish. These results suggested that a shift in prey fish composition from Arctic cod to capelin and/or sand lance is unlikely to reduce the food quality of the prey available to marine predators at least with respect to concentrations of essential fatty acids, selenium, and Se:Hg ratios. Graphical abstract Image 1 Highlights • Essential fatty acids, Se levels and Se:Hg ratios in Arctic vs boreal prey fish. • Boreal capelin and sandlance had similar EPA + DHA, ω 3, and PUFA levels to Arctic cod. • Higher Se levels in sand lance compared to other fish and invertebrates. • Higher Se:Hg molar ratios in sand lance and capelin compared to Arctic cod. • Overall similar nutritional quality in capelin and sand lance compared to cod. [ABSTRACT FROM AUTHOR]

Abstract This study investigated relationships between organohalogen compound (OHC) exposure, feeding habits, and pathogen exposure in a recovering population of Atlantic walruses (Odobenus rosmarus rosmarus) from the Svalbard Archipelago, Norway. Various samples were collected from 39 free-living, apparently healthy, adult male walruses immobilised at three sampling locations during the summers of 2014 and 2015. Concentrations of lipophilic compounds (polychlorinated biphenyls, organochlorine pesticides and polybrominated diphenyl ethers) were analysed in blubber samples, and concentrations of perfluoroalkylated substances (PFASs) were determined in plasma samples. Stable isotopes of carbon and nitrogen were measured in seven tissue types and surveys for three infectious pathogens were conducted. Despite an overall decline in lipophilic compound concentrations since this population was last studied (2006), the contaminant pattern was similar, including extremely large inter-individual variation. Stable isotope ratios of carbon and nitrogen showed that the variation in OHC concentrations could not be explained by some walruses consuming higher trophic level diets, since all animals were found to feed at a similar trophic level. Antibodies against the bacteria Brucella spp. and the parasite Toxoplasma gondii were detected in 26% and 15% of the walruses, respectively. Given the absence of seal-predation, T. gondii exposure likely took place via the consumption of contaminated bivalves. The source of exposure to Brucella spp. in walruses is still unknown. Parapoxvirus DNA was detected in a single individual, representing the first documented evidence of parapoxvirus in wild walruses. Antibody prevalence was not related to contaminant exposure. Despite this, dynamic relationships between diet composition, contaminant bioaccumulation and pathogen exposure warrant continuing attention given the likelihood of climate change induced habitat and food web changes, and consequently OHC exposure, for Svalbard walruses in the coming decades. Graphical abstract Image 1 Highlights • This study was conducted on 39 male Atlantic walruses from Svalbard, Norway. • Stable isotope values indicated that all individuals fed at a low trophic level. • Total lipophilic POP concentrations in blubber ranged from 43.2 to 41554 ng/g lw. • Seroprevalence of anti- Brucella spp. and anti- Toxoplasma gondii antibodies was ≤26%. • Antibody prevalence was not related to exposure to POPs or PFASs. This study reports levels of pollutants in comparison with diet and pathogen exposure in 39 male Atlantic walruses from Svalbard, Norway. [ABSTRACT FROM AUTHOR]

Combining mercury and stable isotope data sets of consumers facilitates the quantification of whether contaminant variation in predators is due to diet, habitat use and/or environmental factors. We investigated inter-species variation in total Hg (THg) concentrations, trophic magnification slope between δ15N and THg, and relationships of THg with δ13C and δ34S in 15 fish and four marine mammal species (249 individuals in total) in coastal Arctic waters. Median THg concentration in muscle varied between species ranging from 0.08 ± 0.04 μg g−1 dw in capelin to 3.10 ± 0.80 μg g−1 dw in beluga whales. Both δ15N (r2 = 0.26) and δ34S (r2 = 0.19) best explained variation in log-THg across consumers. Higher THg concentrations occurred in higher trophic level species that consumed more pelagic-associated prey than consumers that rely on the benthic microbial-based food web. Our study illustrates the importance of using a multi-isotopic approach that includes δ34S when investigating trophic Hg dynamics in coastal marine systems. • THg concentration was lowest in slender eelblenny and highest in beluga. • Trophic magnification slope was comparable to several other Arctic ecosystems. • δ15N and δ34S were better predictors of THg variation across the food web than δ13C. • An isotopic approach with δ34S should be used to examine trophic dynamics of mercury. [ABSTRACT FROM AUTHOR]

Contaminant dynamics within Arctic marine food webs may be altered through the climate-driven northward invasions of temperate/boreal species. Here, we compare tissue concentrations of total mercury (THg) and legacy and emerging persistent organic pollutants (POPs) in native versus invading forage species sampled from 2012 to 2014 near Arviat, Clyde River, and Resolute Bay, NU, representing, low, mid- and high eastern Canadian Arctic regions, respectively. Concentrations of THg, legacy Σ-polychlorinated biphenyls (ΣPCB) and Σ-organochlorine (ΣOC) pesticides were detected in all forage species, whereas emerging halogenated flame retardants were detected in only a few individuals. Concentrations of major contaminant groups among regions did not vary for Arctic cod ( Boreogadus saida ), while for sculpin (Cottoidea) there was no clear latitudinal trend. Thus, considering interspecific variation, native sculpin and northern shrimp ( Pandalus borealis ) had the highest overall concentrations of THg (0.17 ± 0.02 and 0.21 ± 0.01 μg g −1 wet weight, respectively), ΣPCB (322 ± 35 and 245 ± 25 ng g −1 lipid weight (lw), respectively), and ΣOC (413 ± 38 and 734 ± 64 ng g −1 lw, respectively). Comparing the keystone native species, Arctic cod, to its ‘replacement’ species, capelin ( Mallotus villosus ) and sandlance ( Ammodytes spp.), THg concentrations were higher in Arctic cod compared to capelin ( p < 0.001), which was partly explained by differences in fish length. Conversely, capelin and sandlance had higher concentrations of most POPs than Arctic cod ( p < 0.02). Neither feeding habitat (based on δ 13 C), trophic position (based on δ 15 N), nor fish length significantly explained these differences in POPs between Arctic cod, capelin and sandlance. Higher POPs concentrations, as well as variation in congener/compound patterns, in capelin and sandlance relative to Arctic cod seem, therefore, more likely related to a more “temperate”-type contaminant signature in the invaders. Nevertheless, the relatively small (up to two-fold) magnitude of these differences suggested limited effects of these ecological changes on contaminant uptake by Arctic piscivores. [ABSTRACT FROM AUTHOR]

Concentrations of total mercury (THg) and total cadmium (TCd) were determined in muscle and liver of ringed seals ( Pusa hispida ) from up to 14 locations across the Canadian Arctic. Location, trophic position (TP) and relative carbon source best predicted the THg and TCd concentrations in ringed seals. THg concentrations in ringed seals were highest in the western Canadian Arctic (Beaufort Sea), whereas TCd was highest in the eastern Canadian Arctic (Hudson Bay and Labrador). A positive relationship between THg and TP and a negative relationship between THg and relative carbon source contributed to the geographical patterns observed and elevated THg levels at certain sites. In contrast, a negative relationship between TCd and TP was found, indicating that high TCd concentrations are related to seals feeding more on invertebrates than fish. Feeding ecology appears to play an important role in THg and TCd levels in ringed seals, with biomagnification driving elevated THg levels and a dependence on low-trophic position prey resulting in high TCd concentrations. The present study shows that both natural geological differences and diet variability among regions explain the spatial patterns for THg and TCd concentrations in ringed seals. [ABSTRACT FROM AUTHOR]

Greenland sharks ( Somniosus microcephalus ) are large carnivorous sharks that appear to be widely distributed in Arctic seas and in deep, cold temperate waters. In order to examine their movement patterns, diving behaviour and temperature preferences, pop-up archival transmitting tags (PATs) were deployed on 15 Greenland sharks up to 5.1 m in length, both in the Canadian Arctic and in the northwest Atlantic off the eastern coast of Canada. Tags remained on the sharks up to 11 months (mean of 149 days, including four tags which came off prematurely) before popping off. All sharks travelled a minimum of 315 km, and some as much as 1615 km, at depths of up to 1816 m. All tagged Greenland sharks in the Arctic exited the relatively shallow, coastal waters of Cumberland Sound before sexual maturation, presumably moving to spend their adult lives in the deeper waters of the Davis Strait to the north. All the presumably mature Greenland sharks tagged in the NW Atlantic moved up to 1000 km off the continental shelf over abyssal waters to the south. There was extensive evidence of pelagic swimming in both regions, but diel vertical excursions into the water column were not observed. The mean temperature of 2.7 °C recorded in the Arctic sharks was much less than the 7.9 °C mean temperature observed in the Atlantic sharks, where a maximum temperature of 17.2 °C was recorded. Our results indicate that Greenland sharks can inhabit very deep waters, and they can inhabit very cold waters, but they do not necessarily have to inhabit deep, cold waters. It is possible that Greenland sharks migrate offshore over very deep waters to mate and/or give birth. [ABSTRACT FROM AUTHOR]

Polychlorinated biphenyls (PCBs) chiral signatures were measured in Greenland sharks (Somniosus microcephalus) and their potential prey in arctic marine food webs from Canada (Cumberland Sound) and Europe (Svalbard) to assess temporal and spatial variation in PCB contamination at the stereoisomer level. Marine mammals had species-specific enantiomer fractions (EFs), likely due to a combination of in vivo biotransformation and direct trophic transfer. Greenland sharks from Cumberland Sound in 2007–2008 had similar EFs to those sharks collected a decade ago in the same location (PCBs 91, 136 and 149) and also similar to their conspecifics from Svalbard for some PCB congeners (PCBs 95, 136 and 149). However, other PCB EFs in the sharks varied temporally (PCB 91) or spatially (PCB 95), suggesting a possible spatiotemporal variation in their diets, since biotransformation capacity was unlikely to have varied within this species from region to region or over the time frame studied. [Copyright &y& Elsevier]

Persistent organic pollutants (POPs) and stable isotopes were measured in muscle from fledglings of two arctic seabird species, Northern fulmar (Fulmarus glacialis) and Black-legged kittiwakes (Rissa tridactyla). The purpose was to compare POP concentrations between species, in an age class that is highly vulnerable to POPs but little studied, relate to diet using stable isotopes, and quantify differences across life stages (egg to adult). Northern fulmar fledglings had significantly higher POP concentrations than kittiwake, consistent with results reported for adults of these species. Surprisingly, carbon and nitrogen stable isotopes did not differ between species, which does not match data for, or the known feeding ecology, of the adults. Fulmar/kittiwake POP concentration ratios varied across life stages indicating variable POP exposure and accumulation with age in seabirds, indicating that of the use of avian species-specific thresholds should only be done with caution in ecosystem-based POP risk management. [Copyright &y& Elsevier]

Concentrations of POPs in Great skua eggs from Shetland are among the highest in North Atlantic seabirds, with up to 11,600 μg/kg (ww) DDE and up to 17,900 μg/kg ww ∑PCB. Concentrations of legacy POPs were significantly lower in 2008 than 1980. Decreases were greatest for least persistent compounds. Median ∑PBDEs increased from 99 μg/kg ww in 1980 to 173 μg/kg ww in 2008. There were changes in Great skua breeding season diet, with more adult Herring and Mackerel and less Sandeel. These changes increase exposure to POPs, since Herring and Mackerel accumulate more POPs than Sandeels. In both years, eggs with higher δ15N had higher POP concentrations. In 1980, birds feeding more on demersal discard fish from trawl fisheries and less on Sandeels, had higher POP levels in eggs. In 2008, individuals feeding more on Herring and Mackerel, and less on discards, had higher POP levels in eggs. [Copyright &y& Elsevier]

Abstract: To assess geographic distributions of elements in the Arctic we compared essential and non-essential elements in the livers of polar bears (Ursus maritimus) collected from five regions within Canada in 2002, in Alaska between 1994 and 1999 and from the northwest and east coasts of Greenland between 1988 and 2000. As, Hg, Pb and Se varied with age, and Co and Zn with gender, which limited spatial comparisons across all populations to Cd, which was highest in Greenland bears. Collectively, geographic relationships appeared similar to past studies with little change in concentration over time in Canada and Greenland for most elements; Hg and Se were higher in some Canadian populations in 2002 as compared to 1982 and 1984. Concentrations of most elements in the polar bears did not exceed toxicity thresholds, although Cd and Hg exceeded levels correlated with the formation of hepatic lesions in laboratory animals. [Copyright &y& Elsevier]

Abstract: The influence of PCBs on the thyroid status of rainbow trout was assessed at various temperatures to identify if PCB mixtures, as well OH-PCBs produced via biotransformation of parent PCBs, can illicit thyroid effects in fish. Juvenile rainbow trout (Oncorhynchus mykiss) held at 8, 12 or 16°C were exposed to dietary concentrations of an environmentally relevant mixture of PCBs for 30 days followed by a depuration phase. Two additional treatments at 12°C included higher concentrations of PCBs (congeners 77, 126 and 169) known to induce CYP1A in fish (referred to as CYP1A treatment) and PCBs (congeners 87, 99, 101, 153, 180, 183 and 194) known to induce CYP2B in mammals (referred to as CYP2 treatment), to assess the influence of more biologically relevant PCB congeners on thyroid indices in fish. Growth rate and liver somatic index varied with water temperature (p <0.05) but did not differ between PCB exposed and control fish (p >0.05) and mortality was low in all treatments. Changes in some measures of thyroid status were apparent in PCB-exposed fish held in the 12 and 16°C treatments while other measures showed no change in any treatment. The natural inverse relationship between thyroid epithelial cell height (TECH) and temperature, was diminished after 30 days of exposure to PCBs as the epithelial cell height in PCB-exposed fish was significantly augmented in the 12 and 16°C treatments compared to controls at these temperatures (p <0.05). However, after 20 days of depuration, TECH values in the PCB exposed fish returned to control values. The natural linear gradient between T4 outer-ring deiodinase activity (ORD) and temperature was also diminished after 30 days of exposure to PCBs. PCB-exposed fish from the 16°C treatment had significantly lower deiodinase activities (p <0.05) compared to controls at this temperature, but deiodinase activities returned to normal by day 20 of depuration. No differences were observed in T3 inner-ring deiodinase (IRD) activities and plasma concentrations of T3 and T4 in any of the treatments (p >0.05). EROD activity in fish from the CYP1A and CYP2 treatments were elevated compared to control and high dose PCB-exposed treatments (p <0.05), but the inclusion of CYP inducing congeners did not appear to influence any index of thyroid status. Results of this study suggest that exposure of rainbow trout to high concentrations of PCBs and/or OH-PCBs may alter some indices of thyroid status when water temperatures are high, but these changes are within the compensatory scope of the thyroid system based on no change in circulating hormone concentrations, growth rates or mortality. [Copyright &y& Elsevier]

A number of elements/metals have increased in arctic biota and are of concern due to their potential toxicity. Most studies on elements in the Arctic have focused on marine mammals and seabirds, but concentrations in the Greenland shark (Somniosus microcephalus) and Pacific sleeper shark (Somniosus pacificus), the only two shark species known to regularly inhabit arctic waters, have never been reported. To address this data gap, concentrations and patterns of 25 elements were analyzed in liver of Greenland sharks collected about Cumberland Sound (n =24) and Pacific sleeper sharks collected about Prince William Sound (n =14). Several non-essential elements differed between species/locations, which could suggest geographical exposure differences or ecological (e.g., diet) differences between the species. Certain essential elements also differed between the two sleeper sharks, which may indicate different physiological requirements between these closely related shark species, although information on such relationships are lacking for sharks and fish. [Copyright &y& Elsevier]

Abstract: Anthropogenic contaminants have been a concern in the Canadian arctic for over 30 years due to relatively high concentrations of bioaccumulating and biomagnifying organochlorine contaminants (OCs) and toxic metals found in some arctic biota and humans. However, few studies have addressed the potential effects of these contaminants in Canadian arctic wildlife. Prior to 1997, biological effects data were minimal and insufficient at any level of biological organization. The present review summarizes recent studies on biological effects related to contaminant exposure, and compares new tissue concentration data to threshold effects levels. Weak relationships between cadmium, mercury and selenium burdens and health biomarkers in common eider ducks (Somateria mollissima borealis) in Nunavut were found but it was concluded that metals were not influencing the health of these birds. Black guillemots (Cepphus grylle) examined near PCB-contaminated Saglek Bay, Labrador, had enlarged livers, elevated EROD and liver lipid levels and reduced retinol (vitamin A) and retinyl palmitate levels, which correlated to PCB levels in the birds. Circulating levels of thyroid hormones in polar bears (Ursus maritimus) were correlated to PCB and HO-PCB plasma concentrations, but the impact at the population level is unknown. High PCB and organochlorine pesticide concentrations were found to be strongly associated with impaired humoral and cell-mediated immune responses in polar bears, implying an increased infection risk that could impact the population. In beluga whale (Delphinapterus leucas), cytochromes P450 (phase I) and conjugating (phase II) enzymes have been extensively profiled (immunochemically and catalytically) in liver, demonstrating the importance of contaminants in relation to enzyme induction, metabolism and potential contaminant bioactivation and fate. Concentrations of OCs and metals in arctic terrestrial wildlife, fish and seabirds are generally below effects thresholds, with the possible exception of PCBs in burbot (Lota lota) in some Yukon lakes, Greenland shark (Somniosus microcephalus), glaucous and great black-backed gulls (Larus hyperboreus and L. marinus), and TEQs of dioxin-like chemicals in seabird eggs. PCB and DDT concentrations in several arctic marine mammal species exceed effects thresholds, although evidence of stress in these populations is lacking. There is little evidence that contaminants are having widespread effects on the health of Canadian arctic organisms, with the possible exception of polar bears. However, further research and better understanding of organohalogen exposure in arctic biota is needed considering factors such as tissue levels that exceed effects thresholds, exposure to “new” organohalogen contaminants of concern, contaminated regions, and climate change. [Copyright &y& Elsevier]

Organochlorine contaminants (OCs) were determined in liver and fat of seven species of seabirds (Alle alle, Uria lomvia, Cepphus grylle, Rissa tridactyla, Pagophila eburnea, Larus hyperboreus, and Fulmaris glacialis) collected in May/June 1998 from the Northwater Polynya in northern Baffin Bay. OC concentrations ranged over an order of magnitude between seabird species and OC groups, with PCBs having the highest concentrations followed by DDT, chlordane, HCH and ClBz. Positive relationships between δ15N (estimator of trophic level) and OC concentrations (lipid basis) were found for all OC groups, showing that trophic position and biomagnification significantly influence OC concentrations in Arctic seabirds. Concentrations of a number of OCs in particular species (e.g., HCH in P. eburnean) were lower than expected based on δ15N and was attributed to biotransformation. P. eburnea and F. glacialis, which scavenge, and R. tridactyla, which migrate from the south, were consistently above the δ15N–OC regression providing evidence that these variables can elevate OC concentrations. Stable isotope measurements in muscle may not be suitable for identifying past scavenging events by seabirds. OC relative proportions were related to trophic position and phylogeny, showing that OC biotransformation varies between seabird groups. Trophic level, migration, scavenging and biotransformation all play important roles in the OCs found in Arctic seabirds. [Copyright &y& Elsevier]

Juvenile rainbow trout (Oncorhynchus mykiss) (initial weights 2–5 g) were exposed to three dietary concentrations (0, 12.4 and 126 ng g−1, wet weight) of a 14C-labelled 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126) for 30 days followed by 160 days of clean food. We assessed bioaccumulation, histology (liver and thyroid) and biochemical responses (liver ethoxyresorufin-O-deethylase (EROD), liver vitamins (retinoids and tocopherol) and muscle thyroid hormone levels) along with growth and survival. The half-life of PCB 126 in the rainbow trout ranged from 82 to 180 days while biomagnification factors (BMF) ranged from 2.5 to 4.1 providing further evidence that PCB 126 is among the most bioaccumulative PCB congeners. Toluene extractable 14C declined with time in the trout suggesting the possibility of some biotransformation and/or covalent bonding with biological macromolecules. The threshold for liver EROD induction by PCB 126 was approximately 0.1 ng g−1 (wet weight). EROD activities in the low- and high treatments were 9 and 44 times greater than control, respectively, and remained elevated throughout the experiment. EROD activity was correlated with whole body concentrations of PCB 126 although there was evidence of EROD activity suppression in the highly exposed fish. Liver didehydroretinoids and tocopherol concentrations were depressed by the high PCB 126 dose after 30 days exposure. Initially, muscle concentrations of thyroxine (T4) and triiodo-l-thyronine (T3) declined as the fish grew during the experiment, and exposure to PCB 126 accelerated the growth related decline. More information is needed to assess the functional significance of the reduced muscular stores of thyroid hormones. Despite the changes in liver EROD, liver vitamins and muscle thyroid hormones, liver and thyroid histology in trout examined after 30 days exposure and growth parameters were unaffected by PCB 126. This indicates that the functional competences of the physiological factors associated with growth were maintained under the experimental conditions. [Copyright &y& Elsevier]

Highlights a study conducted on the Arctic marine zooplankton Calanus hyperboreus and water samples in the Northwater Polynya to examine the concentration of persistent organic pollutants in them. Concentration of POP found in the zooplankton; Relationship between bioconcentration factor and octanol-water partition coefficient in the zooplankton.

Pollutant concentrations are poorly known for the largest animals on Earth, blue whales Balaenoptera musculus and fin whales Balaenoptera physalus. In this study, concentrations of persistent organic pollutants (POPs) were determined in blubber biopsies and stable isotope values for nitrogen (δ 15N) and carbon (δ 13C) were measured using skin biopsies for 18 blue whales and 12 fin whales sampled in waters surrounding the Svalbard Archipelago, Norway. The samples were collected in summer during the period 2014–2018. POPs were dominated by DDTs, PCBs and toxaphenes, with median concentrations in blue/fin whales being 208/341, 127/275 and 133/233 ng/g lipid weight, respectively. Linear models indicated that pollutant concentrations were 1.6–3 times higher in fin whales than in blue whales, which is likely related to the higher trophic positions of fin whales, as indicated by their higher δ 15N. Lower δ 13C in fin whales suggests that they feed at higher latitudes than blue whales; these values were not correlated with pollutant concentrations. Pollutant levels were approximately twice as high in males compared to females (intraspecifically), which indicates that females of these species offload pollutants to their offspring during gestation and lactation, similar to many other mammalian species. Pollutant concentrations in balaenopterid whales from Svalbard waters were generally much lower than in conspecific whales from the Mediterranean Sea or the Gulf of California, but higher than those in conspecifics from the Antarctic Peninsula. Unlabelled Image • Biopsies were taken from 18 blue whales and 12 fin whales from Svalbard. • Pollutant levels were 1.6–3 times higher in fin whales than in blue whales. • Fin whales fed at a higher trophic level and at higher latitudes than blue whales. • Pollutant levels were twice as high in males as females in both species. • Pollution levels in whales vary substantially regionally. [ABSTRACT FROM AUTHOR]

The deep-sea is increasingly viewed as a lucrative environment for the growth of resource extraction industries. To date, our ability to study deep-sea species lags behind that of those inhabiting the photic zone limiting scientific data available for management. In particular, knowledge of horizontal movements is restricted to two locations; capture and recapture, with no temporal information on absolute animal locations between endpoints. To elucidate the horizontal movements of a large deep-sea fish, a novel tagging approach was adopted using the smallest available prototype satellite tag – the mark-report pop-up archival tag (mrPAT). Five Greenland sharks ( Somniosus microcephalus ) were equipped with multiple mrPATs as well as a standard archival satellite tag (miniPAT) that were programmed to release in sequence at 8–10 day intervals. The performance of the mrPATs was quantified. The tagging approach provided multiple locations per individual and revealed a previously unknown directed migration of Greenland sharks from the Canadian high Arctic to Northwest Greenland. All tags reported locations, however, the accuracy and time from expected release were variable among tags (average time to an accurate location from expected release = 30.8 h, range: 4.9–227.6 h). Average mrPAT drift rate estimated from best quality messages (LQ1,2,3) was 0.37 ± 0.09 m/s indicating tags were on average 41.1 ± 63.4 km (range: 6.5–303.1 km) from the location of the animal when they transmitted. mrPATs provided daily temperature values that were highly correlated among tags and with the miniPAT (70.8% of tag pairs were significant). In contrast, daily tilt sensor data were variable among tags on the same animal (12.5% of tag pairs were significant). Tracking large-scale movements of deep-sea fish has historically been limited by the remote environment they inhabit. The current study provides a new approach to document reliable coarse scale horizontal movements to understand migrations, stock structure and habitat use of large species. Opportunities to apply mrPATs to understand the movements of medium size fish, marine mammals and to validate retrospective movement modeling approaches based on archival data are presented. [ABSTRACT FROM AUTHOR]

Salmonids are ecologically and economically important fishes in Lake Ontario but declines in Alewife (Alosa pseudoharengus), recently the primary prey item, may cause shifts in salmonid diets. Improving our understanding of salmonid trophic niches and diets and whether these have changed over time will provide insight into salmonid foraging patterns, ecology, and management. Using three stable isotopes (δ13C, δ15N and δ34S) and Bayesian models, we estimated core trophic niches, niche overlaps among species, and diets for six salmonid species from Lake Ontario sampled during 2018. We used fin and muscle tissue with different temporal assimilation periods to assess seasonal variability in diet, and investigated salmonid trophic niches and diets among three major spatial units (East, Central, West). Overall, core trophic niches overlapped across all species, except Lake Trout (Salvelinus namaycush). Consistent with previous lake-wide analyses of Lake Ontario salmonid diets, Alewife were the preferred prey fish, although Lake Trout and Atlantic Salmon (Salmo salar) had more varied diets, particularly based on white muscle. Fin-based isotope mixing models predicted greater consumption of shallow (< 30 m depth) Round Goby (Neogobius melanostomus) for Lake Trout, Brown Trout (Salmo trutta), and Rainbow Trout (Oncorhynchus mykiss) than other salmonids, indicating seasonal variation in diets. Lake Trout and Brown Trout also varied across spatial units with greater Round Goby consumption in western Lake Ontario. Spatially distinct diets suggest that Brown Trout and Lake Trout populations should be monitored regionally. Understanding prey consumption trends are important to effectively manage fish populations, especially considering on-going ecological changes in the Great Lakes. [ABSTRACT FROM AUTHOR]

Gravid walleye were sampled from Lake Manitoba and western Lake Superior (St. Louis River) to measure the concentrations of organochlorine contaminants (OCs) in eggs and muscle and to assess the influence of maternal age and size on the transfer of OCs from mother to egg. Concentrations of most OCs in Lake Superior walleye eggs were 1 to 3 orders of magnitude greater than in Lake Manitoba eggs. Toxaphene (meanconcentration (wet weight) plus or minus 1 SE, 1580 plus or minus 462 ng/g) and polychlorinated biphenyls (PCBs) (240 plus or minus 24 ng/g) were the predominant OCs in Lake Superior walleye eggs, whereas DDT and metabolites (eggs 16 plus or minus 1.5 ng/g, muscle 2.1 plus or minus 0.36 ng/g) and PCBs (eggs 9.2 plus or minus 0.83 ng/g, muscle2.0 plus or minus 2.4 ng/g) were the most common OCs in Lake Manitoba walleye eggs and female muscle. Egg size (dry mass) and the concentration of most OCs in Lake Manitoba walleye eggs were positively correlated with female length and age. This relationship was strongest for more hydrophobic OCs (e.g., PCBs) but was not significant for less hydrophobic OCs (e.g., hexachlorocyclohexanes (HCHs)). Neither egg size nor egg OC concentration of Lake Superior walleye were significantly correlated with female length or age. There was no relationship between OC concentrations in muscle tissue and female length or age of Lake Manitoba walleye. OC concentrations in Lake Manitoba walleye eggs were not correlated with concentrations in the muscle tissue of themothers, suggesting that OCs in walleye eggs are derived from various tissues. A positive relationship between the egg:muscle ratio of PCB concentrations and the egg:muscle ratio of lipid in freshwater fishsuggests that the maternal transfer of PCBs in freshwater fish is related to the relative amounts of lipid in the eggs and mother. The transfer of hydrophobic OCs from mother to eggs in freshwater fish appears to vary within and among fish species and with the hydrophobicityof t [ABSTRACT FROM AUTHOR]

Polychlorinated biphenyls (PCBs) in high trophic level species typically reflect the contributions of myriad sources, such that source apportionment is rarely possible. The release of PCBs by a military radar station into Saglek Bay, Labrador contaminated the local marine food web. For instance, while heavier (higher chlorinated) PCB profiles in some ringed seals ( Pusa hispida ) were previously attributed to this local source, differences in feeding preferences among seals could not be ruled out as a contributing factor. Herein, similar fatty acid profiles between those seals with ‘local’ PCB profiles and those with ‘long-range’ or background profiles indicate little support for the possibility that differential feeding ecologies underlay the divergent PCB profiles. Ringed seals appeared to feed predominantly on zooplankton ( Mysis oculata and Themisto libellula ), followed by the dusky snailfish ( Liparis gibbus ), arctic cod ( Boreogadus saida ), and shorthorn sculpin ( Myoxocephalus scorpius ). Principal components analysis (PCA) and PCB homolog profiles illustrated the extent of contamination of the Saglek food web, which had very different (and much heavier) PCB profiles than those food web members contaminated by ‘long-range’ sources. Locally contaminated prey had PCB levels that were higher (2- to 544-fold) than prey contaminated by ‘long-range’ sources and exceeded wildlife consumption guidelines for PCBs. The application of multivariate analyses to two distinct datasets, including PCB congeners ( n = 50) and fatty acids ( n = 65), afforded the opportunity to clearly distinguish the contribution of locally-released PCBs to a ringed seal food web from those delivered via long-ranged transport. Results from the present study strongly suggest that habitat use rather than differences in prey selection is the primary mechanism explaining the divergent PCB patterns in Labrador ringed seals. [ABSTRACT FROM AUTHOR]

Benthic and pelagic food web components in Cumberland Sound, Canada were explored as sources of total mercury (THg) to Greenland Sharks ( Somniosus microcephalus ) via both bottom-up food web transfer and top-down shark feeding behavior. Log 10 THg increased significantly with δ 15 N and trophic position from invertebrates (0.01 ± 0.01 μg·g − 1 [113 ± 1 ng·g − 1 ] dw in copepods) to Greenland Sharks (3.54 ± 1.02 μg·g − 1 ). The slope of the log 10 THg vs. δ 15 N linear regression was higher for pelagic compared to benthic food web components (excluding Greenland Sharks, which could not be assigned to either food web), which resulted from THg concentrations being higher at the base of the benthic food web (i.e., in benthic than pelagic primary consumers). However, feeding habitat is unlikely to consistently influence shark THg exposure in Cumberland Sound because THg concentrations did not consistently differ between benthic and pelagic shark prey. Further, size, gender and feeding behavior (inferred from stable isotopes and fatty acids) were unable to significantly explain THg variability among individual Greenland Sharks. Possible reasons for this result include: 1) individual sharks feeding as generalists, 2) high overlap in THg among shark prey, and 3) differences in turnover time between ecological tracers and THg. This first assessment of Greenland Shark THg within an Arctic food web revealed high concentrations consistent with biomagnification, but low ability to explain intra-specific THg variability. Our findings of high THg levels and consumption of multiple prey types, however, suggest that Greenland Sharks acquire THg through a variety of trophic pathways and are a significant contributor to the total biotic THg pool in northern seas. [ABSTRACT FROM AUTHOR]

Acoustic telemetry (AT) is a rapidly evolving technique used to track the movements of aquatic animals. As the capacity of AT research expands it is important to optimize its relevance to management while still pursuing key ecological questions. A global review of AT literature revealed region-specific research priorities underscoring the breadth of how AT is applied, but collectively demonstrated a lack of management-driven objectives, particularly relating to fisheries, climate change, and protection of species. In addition to the need for more research with direct pertinence to management, AT research should prioritize ongoing efforts to create collaborative opportunities, establish long-term and ecosystem-based monitoring, and utilize technological advancements to bolster aquatic policy and ecological understanding worldwide. Animal tracking provides integral spatiotemporal information that contributes to the growing field of movement ecology. AT is one of the main approaches to track the movements of aquatic animals. The proliferation of AT research and technological innovation have increased the ability to explore ecological and management-related questions. Effective integration of AT data at relevant scales to inform management is still limited by a disconnect between management goals and research objectives, as well as global challenges such as equipment compatibility. A comprehensive global overview of existing AT research identifying the knowledge gaps across regions of the world is necessary to ensure that future research advances aquatic animal science and governance. [ABSTRACT FROM AUTHOR]

Abstract: The Greenland shark (Somniosus microcephalus) is a top predator in Arctic marine ecosystems, and the species bioaccumulates high levels of biomagnifying persistent organic pollutants (POP). In teleost fish, as well as in marine mammals and seabirds, legacy POP have been shown to interfere with the vitamin A and vitamin E homeostasis. Thus, there is the potential for negative health effects from these legacy compounds in Greenland sharks. In the present study we examined associations among plasma levels of legacy POP and plasma vitamin A (retinol [RET], retinyl palmitate [RPA]) and vitamin E (α-tocopherol [α-TOC]) in Greenland sharks from Svalbard, Norway. Plasma levels of POP were on average higher than the hepatic levels previously reported in Greenland sharks from Iceland and Davis Strait, Canada. Levels were also higher than the plasma levels reported in Arctic marine mammals. DDTs (mean 8069ng/g l.w., range: 900–59,707ng/g l.w.), PCBs (mean 5766ng/g l.w., range 1344–16,106ng/g l.w.) and chlordanes (mean 1551ng/g l.w., range: 323–5756ng/g l.w.) had the highest concentrations among the POP groups studied. There were significant inverse relationships between RET concentrations and the concentrations of the dioxin-like compounds PCB-118 and PCB-156/171, and the non-dioxin-like compounds PCB-99 and PCB-128. There were also significant inverse relationships between RPA and 18 of the 38 POP compounds measured. Furthermore, there were significant positive associations between α-TOC and 13 of the 27 PCB congeners. The study suggests that these vitamin systems can be affected by the relatively high POP concentrations exhibited by Greenland sharks at Svalbard. However, the present study is correlative and thus the potential interplay between POP and vitamin dynamics of Greenland sharks must be interpreted cautiously, pending further research on this issue among elasmobranchs. [Copyright &y& Elsevier]

Abstract: Fatty acid (FA) analysis is increasingly being applied to study the feeding ecology of sharks. However, very little knowledge exists regarding how sharks alter dietary FAs prior to incorporation into their tissues, or which tissue provides the most accurate representation of diet. To provide insight into these questions, we compared FAs of muscle, liver and blood (plasma) of 18 individuals of a large elasmobranch, the Greenland shark Somniosus microcephalus (Bloch and Schneider, 1801), to FA profiles of several known prey. Greenland sharks fed predominantly on Greenland halibut (Reinhardtius hippoglossoides, Walbaum 1792) and ringed seal (Pusa hispida, Schreber, 1775) based on stomach contents. Shark muscle FA profiles were the most similar to prey FA profiles, both in relative proportions (e.g. muscle 18:1n−7=7.1±1.0%, ringed seal blubber=7.2±1.2%) and on a μgmg−1 basis (e.g. shark muscle 22:1n−11=47.9±12.0μgmg−1 dw, Greenland halibut muscle =59.9±18.5μgmg−1 dw), indicating direct incorporation of most FAs from the diet. Shark blood plasma FAs also corresponded to prey FAs, and were more similar to shark muscle than liver, which supports the suggestion that muscle FAs were of dietary origin. Shark liver had the most variable FA profiles among individuals and retained higher amounts of long-chain monounsaturated FAs (e.g. 20:1n−9) than were observed in prey. As a consequence, shark liver FAs differed the most from known prey like ringed seal. Our results indicate that the FA profiles of shark tissues will not always match those of dominant prey items, and highlight the use of non-lethal tissues, like muscle and plasma, for studying shark diet using FA analysis. Further work is required to unravel what mechanisms underlie the observed differences in FA profiles and shark–prey FA relationships among different shark species, but data presented here will aid future researchers in more accurately applying FAs to study the diet of large, mobile sharks. [Copyright &y& Elsevier]

Abstract: Locomotory muscle function of ectothermic fishes is generally depressed in cold waters, making them vulnerable to avian and mammalian predators whose body temperature remains high. Paradoxically, Greenland sharks Somniosus microcephalus exhibit the reverse of this usual predator–prey thermal pattern by apparently hunting seals in Arctic waters. To examine whether this species possesses cold-adaptations that enhance its swimming performance, we used data-logging tags to measure swim speed and tail-beat frequency (which reflects muscle-shortening speed) of six free-swimming sharks (204–343kg). For comparison, we compiled these parameters for wild fishes from the literature over a wide body mass range (0.2–3900kg) and examined the scaling relationships using phylogenetically informed statistics. The sharks cruised at 0.34m·s−1 with a tail-beat frequency of 0.15Hz, both of which were the lowest values for their size across fish species. The mean and maximum speed (0.74m·s−1) and acceleration during burst swimming (0.008m·s−2) were much lower than those of seals. Our results indicate that the swimming performance of Greenland sharks is limited by cold waters (~2°C) and insufficient to catch swimming seals. However, Arctic seals sleep in water to avoid predation by polar bears Ursus maritimus, which may leave them vulnerable to this cryptic slow-swimming predator. [Copyright &y& Elsevier]

• Predicted diet differed between biochemical tracers and stomach content analyses. • Multiple diet tracers used together can describe subtle and complex patterns. • Diet tracers with differing timeframes suggest seasonal patterns with less sampling. • Lake trout diet may vary by length, location, sex, and season in Lake Ontario. Understanding trophic interactions is critical for successful resource management. However, studying diet patterns (e.g., spatial and seasonal changes) can require extensive effort. Using individual analyses to interpret patterns may be further complicated by assumptions and limitations of the analytical approach. We investigated and compared predicted adult lake trout (Salvelinus namaycush) diet composition and patterns using stomach content analysis (SCA), fatty acid analysis (FAS), and stable isotope analysis (SIA) individually and simultaneously. The three analyses were conducted for fall-captured fish in Lake Ontario and provided different diet composition estimates; SCA suggested alewife (Alosa pseudoharengus) was dominant by frequency and mass, while FAA and SIA suggested rainbow smelt (Osmerus mordax) contributed the most based on similarity among fatty acid signatures and two-stable isotope (carbon and nitrogen) mixing models, respectively. We hypothesize the disagreement among diet estimates is a result of a seasonal shift in diet variably expressed due to differing extent of time reflected by the diet metric: hours to days for SCA, weeks to months for FAA and several months for SIA. Despite variability in diet composition estimates among methods, similar patterns in lake trout diet were observed among the three diet analyses; the contribution of alewife in lake trout diet was greater for larger individuals and for males compared to females, particularly in the east and northeast regions of the lake where alewife density was relatively low. Thus, the complementary results from the three analyses suggest that length, location, sex, and season all influence lake trout diet. Individually, analyses often failed to identify these patterns in lake trout diet with significance, and some of the patterns have not been observed in previous studies of lake trout diet in Lake Ontario. The thorough description of lake trout diet obtained from a single sampling season demonstrates how simultaneous use of multiple diet analyses may allow investigation of spatial and seasonal diet composition and with reduced sampling effort. [ABSTRACT FROM AUTHOR]

Climate warming and mercury (Hg) are concurrently influencing Arctic ecosystems, altering their functioning and threatening food security. Non-anadromous Arctic char (Salvelinus alpinus) in small lakes were used to biomonitor these two anthropogenic stressors, because this iconic Arctic species is a long-lived top predator in relatively simple food webs, and yet population characteristics vary greatly, reflecting differences between lake systems. Mercury concentrations in six landlocked Arctic char populations on Cornwallis Island, Nunavut have been monitored as early as 1989, providing a novel dataset to examine differences in muscle [Hg] among char populations, temporal trends, and the relationship between climate patterns and Arctic char [Hg]. We found significant lake-to-lake differences in length-adjusted Arctic char muscle [Hg], which varied by up to 9-fold. Arctic char muscle [Hg] was significantly correlated to dissolved and particulate organic carbon concentrations in water; neither watershed area or vegetation cover explained differences. Three lakes exhibited significant temporal declines in length-adjusted [Hg] in Arctic char; the other three lakes had no significant trends. Though precipitation, temperature, wind speed, and sea ice duration were tested, no single climate variable was significantly correlated to length-adjusted [Hg] across populations. However, Arctic char Hg in Resolute Lake exhibited a significant correlation with sea ice duration, which is likely closely linked to lake ice duration, and which may impact Hg processing in lakes. Additionally, Arctic char [Hg] in Amituk Lake was significantly correlated to snow fall, which may be linked to Hg deposition. The lack of consistent temporal trends in neighboring char populations indicates that currently, within lake processes are the strongest drivers of [Hg] in char in the study lakes and potentially in other Arctic lakes, and that the influence of climate change will likely vary from lake to lake. Unlabelled Image • Mercury (Hg) and climate change are concurrently impacting Arctic ecosystems. • We monitored Hg concentrations in landlocked Arctic char from 6 lakes (1989–2018). • Organic carbon in water best explained differences between lakes. • Sea ice and snow fall were strongly linked to Hg in char, but not for all lakes. • Currently, lake-specific processes strongly temper climate effects on [Hg] in fish. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stable isotopes and highly branched isoprenoids were studied in a coastal Arctic food web. • Ringed seals occupied the trophic position of 4.8. • δ34S of higher trophic level pelagic organisms indicated reliance on both benthic and pelagic food sources. • 53 ± 22.2 % of marine mammal diet is derived from carbon fixed by ice algae. • Climate change could significantly threaten ice algal production and alter Arctic coastal food webs. Climate-driven alterations of the marine environment are most rapid in Arctic and subarctic regions, including Hudson Bay in northern Canada, where declining sea ice, warming surface waters and ocean acidification are occurring at alarming rates. These changes are altering primary production patterns that will ultimately cascade up through the food web. Here, we investigated (i) the vertical trophic structure of the Southampton Island marine ecosystem in northern Hudson Bay, (ii) the contribution of benthic and pelagic-derived prey to the higher trophic level species, and (iii) the relative contribution of ice algae and phytoplankton derived carbon in sustaining this ecosystem. For this purpose, we measured bulk stable carbon, nitrogen and sulfur isotope ratios as well as highly branched isoprenoids in samples belonging to 149 taxa, including invertebrates, fishes, seabirds and marine mammals. We found that the benthic invertebrates occupied 4 trophic levels and that the overall trophic system went up to an average trophic position of 4.8. The average δ34S signature of pelagic organisms indicated that they exploit both benthic and pelagic food sources, suggesting there are many interconnections between these compartments in this coastal area. The relatively high sympagic carbon dependence of Arctic marine mammals (53.3 ± 22.2 %) through their consumption of benthic invertebrate prey, confirms the important role of the benthic subweb for sustaining higher trophic level consumers in the coastal pelagic environment. Therefore, a potential decrease in the productivity of ice algae could lead to a profound alteration of the benthic food web and a cascading effect on this Arctic ecosystem. [ABSTRACT FROM AUTHOR]

Chinook salmon (Oncorhynchus tshawytscha) have been observed to spatially segregate based on body size in the marine environment. In their introduced range in the Laurentian Great Lakes, where Chinook salmon support important recreational fisheries, very little is known about their seasonal habitat use, including effects of body size on horizontal and vertical distributions. This study quantified the seasonal home ranges and distributions by depth and temperature of two size classes of Chinook salmon in Lake Ontario using pop-off data storage tags (pDST) from 2014 to 2016 and acoustic telemetry from 2017 to 2020. Moderate overlap occurred between immature (age classes 1 and 2) and sub-adult (age classes 3 and 4) individuals at the 50% home range level, a measure of horizontal segregation, with the greatest segregation during the fall and spring. Depth and temperature occupancy for two immature individuals in fall and winter also differed from those of sub-adults. This study is the first to examine the overlap in horizontal and vertical distributions between Chinook salmon size classes in the Great Lakes and contributes key information on their depth and temperature distributions. [ABSTRACT FROM AUTHOR]

Conservation concern regarding the overharvest of global shark populations for meat and fin consumption largely surrounds documented deleterious ecosystem effects, but may be further supported by improved knowledge of possibly high levels in their edible tissues (particularly meat) of the neurotoxin, methylmercury (CH 3 Hg). For many regions, however, little data exist on shark tissue Hg concentrations, and reasons for Hg variation within and among species or across regions are poorly understood. We quantified total Hg (THg) in 17 shark species (total n = 283) from the east coast of South Africa, a top Hg emitter globally. Concentrations varied from means of around 0.1 mg kg − 1 dry weight (dw) THg in hardnose smoothhound ( Mustelus mosis ) and whale ( Rhincodon typus ) sharks to means of over 10 mg kg − 1 dw in shortfin mako ( Isurus oxyrinchus ), scalloped hammerhead ( Sphyrna lewini ), white ( Carcharodon carcharias ) and ragged-tooth ( Carcharias taurus ) sharks. These sharks had higher THg levels than conspecifics sampled from coastal waters of the North Atlantic and North, mid-, and South Pacific, and although sampling year and shark size may play a confounding role, this result suggests the potential importance of elevated local emissions. Values of THg showed strong, species-specific correlations with length, and nearly half the remaining variation was explained by trophic position (using nitrogen stable isotopes, δ 15 N), whereas measures of foraging habitat (using carbon stable isotopes, δ 13 C) were not significant. Mercury concentrations were above the regulatory guidelines for fish health effects and safe human consumption for 88% and 70% of species, respectively, suggesting on-going cause for concern for shark health, and human consumers of shark meat. [ABSTRACT FROM AUTHOR]

Temporal variation characterizes many of Earth's ecosystems. Despite this, little is known about how food webs respond to regular variation in time, such as occurs broadly with season. We argue that season, and likely any periodicity, structures food webs along a temporal axis in an analogous way to that previously recognized in space; predators shift their diet as different resource compartments and trophic levels become available through time. These characteristics are likely (i) central to ecosystem function and stability based on theory, and (ii) widespread across ecosystem types based on empirical observations. The temporal food web perspective outlined here could provide new insight into the ecosystem-level consequences of altered abiotic and biotic processes that might accompany globally changing environments. [ABSTRACT FROM AUTHOR]

Knowledge of the feeding ecology and trophic interactions of marine species is essential to understanding food web dynamics and developing ecosystem-based management approaches. Given that many top predatory fishes have experienced large population declines from coastal ecosystems, it is critical to understand the role of smaller, mesopredators in coastal food webs. This study used stomach content (SCA) and stable isotope analyses (SIA) of muscle tissue (δ 13 C, δ 15 N) to examine the feeding ecology of four common demersal elasmobranchs ( Mustelus henlei , Raja velezi , Zapteryx xyster and Torpedo peruana ) from the Pacific coast of Costa Rica, Central America. Specifically, we investigated: ( i ) size- and sex-related changes in diet; ( ii ) dietary changes between seasons; ( iii ) dietary changes across depth and latitudinal gradients; and ( iv ) the degree of diet overlap among species. SCA showed that M. henlei , R. velezi and Z. xyster were feeding on a wide range of teleost and decapod species, whereas teleosts dominated the diet of T. peruana . Torpedo peruana had a lower prey diversity and dietary breath than the other species. Interestingly, SIA revealed a significantly larger isotopic niche breath in Z. xyster , indicating that SIA can provide a broader perspective of diet than SCA. Both SCA and SIA showed relatively low dietary overlap among species, except between R. velezi and Z. xyster which have a similar size, mouth morphology and potentially feeding behaviour. Latitude and size were identified as important drivers of the feeding ecology of elasmobranchs; however, their effect varied considerably among species and was often influenced by other factors such as sex and depth. Season had little influence on elasmobranch diet, but our data suggested that isotopic baseline values differ between geographic regions due to differences in local biogeochemical processes and/or prey availability, and possibly in response to seasonal nutrient fluctuations. This may also indicate that some of these elasmobranchs tend to use more localized habitats along the coast. The present study increased our understanding of the feeding ecology of common demersal elasmobranch species. Moreover, trophic information of elasmobranchs provided an important baseline record to understanding how trawling fisheries may impact demersal ecosystems in Costa Rica and the Central American region. [ABSTRACT FROM AUTHOR]

Abstract: Given the known effect of lipid content on δ13C values and the potential effect of urea on δ15N values, examining the effects of lipid extraction, which can potentially extract both, is of particular importance for elasmobranch isotope ecology. Through analysing paired δ13C, total %C, δ15N, total %N and C:N values of non-lipid extracted (BULK) and lipid extracted (LE) muscle samples from twenty-one elasmobranch species, we assessed whether lipid extraction was required: (i) to remove lipids given reported low lipid content and, (ii) to determine if δ15N values were affected and whether this relates to the retention of isotopically light urea by elasmobranchs. The mean (±SD) δ13C values of eight out of twenty-one species significantly increased following lipid extraction with two species, the Greenland (Somniosus microcephalus) and whale (Rhincodon typus) shark, showing a marked increase (5.0±0.4‰ and 3.3‰, respectively). The mean (±SD) and maximum increase in δ13C values were 0.6±1.2‰ and 5.9‰, respectively. For δ15N data, thirteen species showed a significant increase following lipid extraction and a concomitant reduction in total percent nitrogen (%N). The C:N ratio for these species also increased from unexpectedly low values of <3.0 to ~3.0, the value expected for pure protein. The mean and maximum observed increase in δ15N values were 0.6±0.6‰ and 2.3‰, respectively. There was no effect of increasing animal size on δ13C and δ15N difference (LE–BULK) for the two species examined. Field sampled animals (sampled immediately upon capture in the marine environment) showed a greater δ15N difference than animals sampled in the laboratory (sampled several hours after capture in the marine environment) (1.0±0.5‰ and 0.4±0.4‰ respectively), while estuarine sampled animals (sampled immediately) showed the smallest difference (0.1±0.6‰). The δ13C data demonstrate that lipid extraction is required to remove lipids from elasmobranch muscle tissue given both intra- and inter- species variability. In addition, the increase in δ15N values, decrease in %N and increase in C:N ratio indicate that lipid extraction is removing soluble urea. Given lower δ15N diet-tissue discrimination factors for large marine predators, removal of urea is required to elucidate accurate trophic position estimates and relative food web position of elasmobranchs and for diet reconstruction. It is recommended that investigators undertake lipid extraction trials on elasmobranch muscle tissue to determine effects on δ13C and δ15N values on a species-by-species basis. [Copyright &y& Elsevier]

Abstract: Stable isotopes (δ 15N and δ 13C) are being widely applied in ecological research but there has been a call for ecologists to determine species- and tissue-specific diet discrimination factors (∆13C and ∆15N) for their study animals. For large sharks stable isotopes may provide an important tool to elucidate aspects of their ecological roles in marine systems, but laboratory based controlled feeding experiments are impractical. By utilizing commercial aquaria, we estimated ∆15N and ∆13C of muscle, liver, vertebral cartilage and a number of organs of three large sand tiger (Carcharias taurus) and one large lemon shark (Negaprion brevirostris) under a controlled feeding regime. For all sharks mean±SD for ∆15N and ∆13C in lipid extracted muscle using lipid extracted prey data were 2.29‰±0.22 and 0.90‰±0.33, respectively. The use of non-lipid extracted muscle and prey resulted in very similar ∆15N and ∆13C values but mixing of lipid and non-lipid extracted data produced variable estimates. Values of ∆15N and ∆13C in lipid extracted liver and prey were 1.50‰±0.54 and 0.22‰±1.18, respectively. Non-lipid extracted diet discrimination factors in liver were highly influenced by lipid content and studies that examine stable isotopes in shark liver, and likely any high lipid tissue, should strive to remove lipid effects through standardising C:N ratios, prior to isotope analysis. Mean vertebral cartilage ∆15N and ∆13C values were 1.45‰±0.61 and 3.75‰±0.44, respectively. Organ ∆15N and ∆13C values were more variable among individual sharks but heart tissue was consistently enriched by ~1–2.5‰. Minimal variability in muscle and liver δ 15N and δ 13C sampled at different intervals along the length of individual sharks and between liver lobes suggests that stable isotope values are consistent within tissues of individual animals. To our knowledge, these are the first reported diet–tissue discrimination factors for large sharks under semi-controlled conditions, and are lower than those reported for teleost fish. [Copyright &y& Elsevier]