Muscle δ13C Research Articles

Novel insights into the diet of southern stingrays and Caribbean whiptail rays

Caribbean whiptail and southern stingrays are large-bodied mesopredators, occupying shallow, nearshore ecosystems of The Bahamas, yet virtually nothing is known of their diet or potential resource competition. We used stomach content analysis via gastric lavage and stable isotope analysis to investigate the diet of 94 Caribbean whiptail rays Styracura schmardae and 112 southern stingrays Hypanus americanus across 3 locations in the central Bahamas. Gastric lavage was used to identify prey consumed and compared to stable isotope analysis of δ15N, δ13C and δ34S of barb, muscle, blood and skin, representing different temporal integration periods. Both species appeared to consume a majority of crustaceans and annelids, although δ13C values suggested that Caribbean whiptail rays have larger isotopic niche space across isotopes sampled (potentially broader diet) than southern stingrays, ranging from 5.82-3.43‰2, and a greater variance in δ13C. This suggests Caribbean whiptail rays potentially feed on prey from either a wider geographic range or from different habitats. Caribbean whiptail and southern stingrays are known to spatio-temporally overlap, and their isotopic niche overlapped by 35.6%. This study represents the first integrated diet estimate for southern stingrays obtained using multiple techniques, and the first ever diet assessment in Caribbean whiptail rays. These data are critical for conservation of coastal ray species and management of coastal and nearshore environments throughout the region.

Evidence of energy and nutrient transfer from invasive pink salmon (Oncorhynchus gorbuscha) spawners to juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in northern Norway

AbstractRecent large influxes of non‐native Pacific pink salmon (Oncorhynchus gorbuscha) to North European rivers have raised concern over their potential negative impacts on native salmonids and recipient ecosystems. The eggs and carcasses of semelparous pink salmon may provide a significant nutrient and energy subsidy to native biota, but this phenomenon has not been widely documented outside the species' native distribution. We analysed the stomach contents and stable isotope values (δ15N and δ13C) in muscle and liver tissues of juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) to determine whether these native salmonids utilise marine‐derived nutrients and energy provided by pink salmon eggs and carcasses in the subarctic river system Vesterelva, northern Norway. Although egg foraging and assimilation of marine‐derived nutrients in fish body tissues were found to be minor at the population level, a few juvenile salmon and trout had recently eaten large quantities of pink salmon eggs. Some of these individuals also had high δ15N and δ13C values, indicating a long‐term diet subsidised by marine‐derived nutrients and energy from pink salmon eggs. Hence, our study provides novel evidence that the eggs of invasive pink salmon may provide an energetic, profitable food resource for juvenile native fish. More research is needed to understand the broader ecological implications for fishes and other biota in river ecosystems invaded by pink salmon.

Stable mercury concentrations of tropical tuna in the south western Pacific ocean: An 18-year monitoring study

Global anthropogenic mercury (Hg) emissions to the atmosphere since industrialization are widely considered to be responsible for a significant increase in surface ocean Hg concentrations. Still unclear is how those inputs are converted into toxic methylmercury (MeHg) then transferred and biomagnified in oceanic food webs. We used a unique long-term and continuous dataset to explore the temporal Hg trend and variability of three tropical tuna species (yellowfin, bigeye, and skipjack) from the southwestern Pacific Ocean between 2001 and 2018 (n = 590). Temporal trends of muscle nitrogen (δ15N) and carbon (δ13C) stable isotope ratios, amino acid (AA) δ15N values and oceanographic variables were also investigated to examine the potential influence of trophic, biogeochemical and physical processes on the temporal variability of tuna Hg concentrations. For the three species, we detected significant inter-annual variability but no significant long-term trend for Hg concentrations. Inter-annual variability was related to the variability in tuna sampled lengths among years and to tuna muscle δ15N and δ13C values. Complementary AA- and model-estimated phytoplankton δ15N values suggested the influence of baseline processes with enhanced tuna Hg concentrations observed when dinitrogen fixers prevail, possibly fuelling baseline Hg methylation and/or MeHg bioavailability at the base of the food web. Our results show that MeHg trends in top predators do not necessary capture the increasing Hg concentrations in surface waters suspected at the global oceanic scale due to the complex and variable processes governing Hg deposition, methylation, bioavailability and biomagnification. This illustrates the need for long-term standardized monitoring programs of marine biota worldwide.

Differential habitat use patterns of yellow perch Perca flavescens in eastern Lake Michigan and connected drowned river mouth lakes

Understanding stock structure and habitat use is important for sustainable fisheries management and conservation of genetic and phenotypic diversity. In eastern Lake Michigan, yellow perch Perca flavescens is found in both the nearshore region of Lake Michigan proper and drowned river mouth (DRM) lakes, small estuary-like systems directly connected to Lake Michigan. Recent genetic analyses suggest complex stock structure between these habitats and the potential migration of Lake Michigan yellow perch into the profundal zone of DRM lakes. We quantified carbon (δ13C) and oxygen (δ18O) stable isotope ratios of yellow perch otolith cores to index natal origins, and measured muscle δ13C, nitrogen (δ15N), δ18O, and hydrogen (δ2H) isotope ratios to reflect recent diet and habitat use. Stable isotope ratios of otolith cores and muscle samples support the existence of resident populations in nearshore Lake Michigan and DRM lakes, as well as Lake Michigan migrants using DRM lakes. Most fish caught in DRM lakes that had natal and recent stable isotope values similar to Lake Michigan fish were collected during fall in DRM lake profundal zones. Comparison of otolith core and muscle stable isotope ratios of individual yellow perch suggest that individuals that recently migrated to DRM lakes also spent early life in Lake Michigan. Differential habitat use patterns of yellow perch in eastern Lake Michigan may have important implications for harvest estimates and fishing regulations. Migration by Lake Michigan fish into DRM lakes does not appear to be related to reproduction, and the underlying benefits of these migrations remain unclear.

Discrimination of nursery locations of juvenile Japanese flounder Paralichthys olivaceus on the Pacific coast of northern Japan based on carbon and nitrogen stable isotope ratios

To test whether stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) can be used to understand the ecological connectivity of Japanese flounder Paralichthys olivaceus, we evaluated the isotopic signatures of juvenile P. olivaceus from the Pacific coast of northern Japan (i.e., from Aomori to Ibaraki Prefectures). We measured δ13C and δ15N in muscle and collagen extracted from vertebrae and found that isotope ratios were strongly correlated in both. The discrimination models we developed for muscle and collagen proved useful in distinguishing among juvenile P. olivaceus collected from the five prefectures (Aomori, Iwate, Miyagi, Fukushima, and Ibaraki). Juveniles collected in Aomori in particular showed significantly lower values of δ13C and δ15N than those from the other prefectures, which likely reflects the greater influence of the Tsugaru Warm Current in that region. Because collagen in the vertebral centrum can be used to reconstruct annual isotopic records, our results may also assist in developing migration tracking procedures for adult P. olivaceus along the Pacific coast of northern Japan.

Maternal and embryonic trace element concentrations and stable isotope fractionation in the smalleye smooth-hound (Mustelus higmani)

Here, we evaluate maternal offloading of 16 trace elements (Essential: Co, Cr, Cu, Fe, Mn, Ni, Se and Zn; Nonessential: Al, As, Ba, Cd, Hg, Pb, Tl and U) and determine mother-offspring isotopic fractionation of δ13C and δ15N in muscle and liver tissue of four pregnant Mustelus higmani and 18 associated embryos sampled from the Amazon Coast of Brazil. Embryo muscle tissue had significantly higher concentrations of most trace elements when compared to mothers, with the exception of Hg. Embryo liver accumulated more nonessential elements than muscle (n = 7 vs. 0, respectively), while the Se:Hg molar ratio was >1 in liver and muscle of both mothers and embryos. Livers of embryos were moderately enriched in δ13C and δ15N when compared to that of their mother. Negative correlations were observed between embryo body length and δ13C and trace elements concentrations. We conclude that mothers offload a large portion of all essential elements and Al, As and Pb to their young and that the isotopic fractionation of embryos reflects maternal diet and habitat occupied, with δ13C diluted with embryonic growth. We also show that muscle and liver accumulate trace elements at different rates relative to the body length of embryos. The Se:Hg molar ratio suggests that Se could play a protective role against Hg toxicity during early stages of M. higmani embryonic development.

The effects of lipid extraction on δ13C and δ15N values and use of lipid‐correction models across tissues, taxa and trophic groups

Abstract Lipid‐rich animal tissues have low δ13C values, which can lead to inaccurate ecological inferences. Chemical lipid extraction (LE) or correction models account for this depletion, but the need for LE or correction is tissue‐ and species‐specific. Also, LE can alter δ15N values, increasing labour and costs because bulk samples must be analysed for δ15N values separately. We studied the effects of LE on δ13C and δ15N values in liver, muscle and skin of common bottlenose dolphins Tursiops truncatus and West Indian manatees Trichechus manatus, two ecologically important species that occupy different trophic levels. We fit lipid‐correction models to each species. We also performed a meta‐analysis to more broadly determine the effects of LE across taxa, tissues and trophic groups (carnivores, omnivores and herbivores) and to fit lipid‐correction models to different taxonomic and trophic groups. Lipid extraction increased the δ13C values in dolphin tissues but had little effect on manatee tissues and no effect on the δ15N values in either species. A mass balance lipid‐correction model best fit the data from all dolphin tissues, and a linear model best fit data for manatee liver while null models best fit data from manatee muscle and skin. Across 128 terrestrial and aquatic species, the effects of LE varied among tissues and were lower for herbivores compared to carnivores. The best‐fitting lipid‐correction models varied among tissue, taxa and trophic groups. Finally, the δ15N values from muscle and liver were affected by LE. Our results strengthen the growing body of evidence that the need for LE is tissue‐ and species‐specific, without a reliable C:N ratio predictive threshold. The prediction errors of lipid‐correction models generally decreased with taxonomic and trophic specificity. The smaller effects of LE in herbivores may be due to differences in diet composition or the physiology of lipid synthesis in members of this trophic group. These results suggest that researchers should use the most species‐, tissue‐ and trophic group‐specific information on LE available and, if not available, perform LE on a subset of samples prior to analysis to determine effects.

Assessing the relationship between diet and size-at-age in Pacific halibut (Hippoglossus stenolepis) using δ13C and δ15N analysis

The ecological mechanisms driving an observed decline in the mean size-at-age of adult Pacific halibut (Hippoglossus stenolepis) in the eastern North Pacific Ocean have yet to be defined. Here, we present the results of a study designed to investigate the relationship between one potential mechanism — diet — and size-at-age using carbon and nitrogen stable isotope analysis. Our results indicate significant differences in the skeletal muscle δ13C and δ15N values between size-at-age categories for each sex, with larger-size-at-age fish consuming diets with higher δ15N values, indicating higher trophic level feeding. Analysis of Bayesian standard ellipse areas showed that for females, intermediate size-at-age categories have the largest dietary range. For males, the largest dietary range was observed in the largest size-at-age category. Our results suggest a size-based stratification in dietary strategy for Pacific halibut with implications for observed declines in size-at-age.

Stomach content and stable isotopes reveal an ontogenetic dietary shift of young-of-the-year scalloped hammerhead sharks (Sphyrna lewini) inhabiting coastal nursery areas

Sphyrna lewini is a placental viviparous shark that uses coastal nursery areas in Jalisco, Mexico, where pups stay 4–12 months. Changes in size or swimming speed may be reflected in diet composition. The main objectives of this study were as follows: (1) analyze the differences in trophic ecology of juvenile S. lewini from coastal nursery areas of Jalisco by sex and size, through stomach content and stable isotope analyses; and (2) analyze changes in muscle and liver δ15N and δ13C values with shark size. Samples were collected from the artisanal fishery from September 2013 to December 2016. Three size classes were compared: neonates, stretched total length (STL) ≤ 75 cm, and STL > 75 cm (75–100 cm). Bony fishes were the most important group in all size classes, and the importance of shrimps decreased with STL. Significant differences in diet composition were found between neonates and STL > 75 cm, which showed the lowest niche overlap (0.32). STL ≤ 75 cm showed the largest niche width (0.75). The δ15N muscle and liver values declined with total length, reflecting the maternal isotopic signal. No differences in liver δ13C values were observed among size classes, but larger size class showed higher muscle δ13C values. Both isotope and stomach content analyses classified all sharks as tertiary consumers, but the trophic position (TP) estimated using δ15N was higher in neonates. No significant differences in the diet and TP were observed between sexes. The liver C:N ratio decreased sharply with STL up to 55 cm, from which increased smoothly, reflecting the lipid reserves consumed during their neonatal stage.

Mercury Bioaccumulation in Lacustrine Fish Populations Along a Climatic Gradient in Northern Ontario, Canada

Climate change is predicted to alter many processes in boreal aquatic ecosystems, including mercury (Hg) bioaccumulation in fish. We investigated current patterns in fish Hg across a climatic gradient in northern Ontario, Canada, to assess the possible influence of further climate change. Cohabiting populations of walleye (a piscivore) and white sucker (a benthivore) were sampled from lakes spanning over 9.0° of latitude (45° 24′ N–54° 20′ N). Latitudinal trends were evident in climatic conditions, as well as several other ecosystem characteristics over this range. Muscle total Hg concentration ([THg]) was modelled with respect to climatic variables as well as other physical, chemical, and biological variables, and all models were ranked by Akaike information criterion. Neither long-term mean temperature nor precipitation was a strong predictor of current muscle [THg] in either species across this region. Instead, drainage basin characteristics (for example, mean slope) and lake water chemistry (for example, [DOC], [SO4]) were the strongest predictors, followed by fish biological traits (for example, muscle δ13C). Walleye [THg] was more strongly related to water chemistry, and white sucker [THg] was more strongly related to drainage basin physical characteristics. For both species, muscle [THg] showed unimodal relationships with several predictors (for example, latitude, [SO4], [DOC]), peaking in their mid-ranges. Fish [THg] is not strongly associated with current climatic conditions across northern Ontario but may be influenced by climate change in future through indirect effects on water chemistry and food web structure.

Influence of life-history-dependent migration strategies on Atlantic salmon diets

AbstractMigratory behaviour may vary according to the life history and demographic attributes of fish and lead to the spatial segregation of distinct population segments during the non-breeding season. In adult Atlantic salmon, spawning history differences are associated with intra-population variation in marine movements, but the degree of connectivity in spatial resource use among and within maiden and repeat spawning salmon is not well understood. We analysed muscle fatty acids (FAs), δ13C and δ15N of Atlantic salmon returning to spawn, and found significant differences among spawning histories. Maiden and alternate repeat spawning Atlantic salmon were differentiated from consecutive repeat spawners by fatty acid biomarkers associated with distinct biogeographic regions of the Labrador Sea, consistent with differential migration and divergent feeding locations. The presence and pattern of feeding contrasts among spawning history groups were further supported by dorsal muscle δ15N, which covaried with FA compositional values and distinguished consecutive repeat spawners from the two other groups. Because the degree of connectivity among population segments affects the ecological factors faced by such groups, an improved understanding of differential migration is necessary to better predict potential population responses to environmental change.

New insight into light-enhanced calcification in mytilid mussels, Mytilus sp., infected with photosynthetic algae Coccomyxa sp.: δ13C value and metabolic carbon record in shells

The posterior shell edge (PSE) of wild mytilid mussels that are highly infected with unicellular photosynthetic green algae Coccomyxa sp. exhibits an extra shell material (ESM). A recently proposed mechanism of ESM formation shows similarity with light-enhanced calcification (LEC), i.e., algae photosynthesis mediates low respiratory CO2 level in shell calcification site (PSE) to promote ESM precipitation. The present study evaluates if infection with algae may affect the δ13C content and metabolic carbon (CM) contribution to shells (PSE) in mussels from the Lower St. Lawrence Estuary, Québec, Canada. Environmental conditions may influence shell δ13C records. To underline possible algae photosynthesis effects, mantle, adductor muscle and shell δ13C are analyzed in infected and non-infected mussels collected from two sites with different salinities, seawater dissolved inorganic carbon (DIC) content, and hydrodynamic regimes. Shell δ13C and tissue δ13C correlate with seawater DIC and salinity. Shell δ13C values are lowest in non-infected mussels, whereas tissues δ13C values show the opposite relationship; in both cases, differences between δ13C values in non-infected and infected mussels are about 0.5‰. The percentage of CM incorporated into shell is higher (ca. 18%) for non-infected mussels than infected mussels (ca. 15%). Literature on the subject suggests that increased δ13C content and decreased %CM in shells of infected mussels must be related to algal photosynthetic activity. Our findings show that shell δ13C records permit the interpretation of ESM formation via LEC.

Diet and isotopic niche overlap elucidate competition potential between seasonally sympatric phocids in the Canadian Arctic

Interspecific interactions may be altered as a result of poleward species range shifts caused by climate change. In recent decades, Cumberland Sound, Nunavut, in the Canadian Arctic, has undergone concurrent increases in the availability of the forage fish capelin (Mallotus villosus) and the number of migratory harp seals (Pagophilus groenlandicus) during the open-water period; however, the impacts of these changes on endemic Arctic species, such as ringed seals (Pusa hispida), have received little attention. We coupled stomach contents with stable isotope analysis (δ13C and δ15N) of muscle and liver to determine the extent of potential competition between ringed seals (n = 91) and harp seals (n = 39) in Cumberland Sound. Isotopic niche breadth was greater for ringed seals (95% ellipse: 10.08‰2) than for harp seals (95% ellipse: 8.00‰2), and harp seal isotopic niche overlapped more with ringed seal isotopic niche than vice versa, suggesting asymmetrical competition potential. Although there was high overlap in isotopic niche breadth (range 50.3–91.0%) and prey species consumed (Schoener’s Index 0.60), stomach content analysis revealed differences in prey species proportions and size composition, thereby reducing the degree of realized niche overlap. Harp seals consumed a higher biomass of fish (66.7%) than did ringed seals (31.9%), and harp seals also consumed larger capelin (64–200 mm), polar cod (Boreogadus saida; 28–194 mm), and Liparidae (55–115 mm) than ringed seals (63–154 mm, 20–189 mm, and 16–128 mm, respectively). With climate change and range shifts predicted to continue into the future, our results provide an important baseline for future studies examining interspecific interactions.

Effects of temperature on tissue–diet isotopic spacing of nitrogen and carbon in otolith organic matter

Reconstruction of the trophic position of a fish can be performed by analysing stable nitrogen and carbon isotopes in otolith protein. However, ambient temperature may affect the tissue–diet isotopic spacing of stable isotopes from diet to predator tissue and bias estimates of trophic position. To test this, otolith protein, heart and muscle tissue from a rearing experiment with juvenile cod held at different temperatures (4, 7, 10 and 14°C) were analysed. There was no significant effect of temperature on otolith δ15N, whereas muscle and heart exhibited a slight decrease in δ15N values with increasing temperature corresponding to maximum of 0.6‰ over the 10°C range. By contrast, the otolith protein δ13C values at 4 and 7°C were significantly higher than for 10 and 14°C, suggesting an approximate 1‰ increased tissue–diet enrichment at the lower temperatures. Temperature had no significant effect on muscle and heart δ13C values. Considering the annual mean variation in ocean temperatures, our results indicate that the trophic signals recorded in the otoliths will reflect changes in diet isotope values with little bias from the ambient temperature experienced by the fish.

Metabolic effects on carbon isotope biomarkers in fish

Carbon stable isotopes (δ13C) in animal tissues are a powerful tool for tracking biological and environmental change. However, carbon isotope signatures can be altered by both physiological and environmental factors which can cloud interpretation in their use as biomarkers. We investigated metabolic effects (by varying temperatures) on δ13C of three fish tissues (otolith, muscle and liver) and the proportional contributions of environmental water (dissolved inorganic carbon; DIC) and diet (metabolic sources). Juvenile Australasian snapper (Chrysophrys auratus) were laboratory-reared at four temperatures for up to two months and then δ13C in otolith, liver and muscle were measured using isotope-ratio mass spectrometry (IRMS). Temperature significantly altered δ13C signatures in all tissues. δ13C in otoliths reflected carbon signatures from diet and water DIC, with values and variation of proportional contributions influenced by temperature. In muscle and liver, we found differences in δ13C between tissues and across temperature treatments with concurrent high diet-to-tissue fractionation. We conclude that metabolic effects influenced carbon incorporation for all tissues, with otolith carbon providing valuable insights into field metabolic rates. However, metabolic effects complicated the use of soft-tissue to track diet. This study deepens our understanding of internal and external drivers of carbon isotopic signatures in fish tissues and enhances their utility as a biomarker in the field. Improved insight into biomarkers facilitates more accurate predictions of ecological and environmental change for better understanding and management of wild populations.

Bioaccumulation characteristics of mercury in fish in the Three Gorges Reservoir, China

Newly constructed reservoirs were recognized as hotspot of mercury (Hg) methylation, and then methylmercury (MeHg) accumulation in food chains. The risk of elevated MeHg concentrations in fish is one of the most important concerns in newly constructed reservoirs. The Three Gorges Reservoir (TGR) is one of the largest reservoirs in the world. However, the distribution and bioaccumulation characteristics of Hg species within the food chains and its potential ecological risk in the TGR remain poorly understood. In this study, 264 fish individuals covering 18 species were collected from the TGR. Total mercury (THg) and MeHg concentrations in different organs (gill, heart, liver, muscle and swim bladder) of fish species were analyzed; the values of δ13C and δ15N in fish muscle were determined as well to reveal the biomagnification properties of Hg in food chains. Our results showed that concentrations of THg (0.5–272 ng g−1, w.w.) and MeHg (0.1–199 ng g−1, w.w.) in fish muscle from the TGR ubiquitously fall below the safe fish consumption limit on Hg recommended by WHO (500 ng g−1, w.w.) and the US-EPA Water Quality Criterion for MeHg (300 ng g−1, w.w.). The short food web jointly with the limited trophic magnification factor in the TGR explained the relatively low Hg concentrations in predators. Among the five fish organs, muscle represented the highest Hg concentrations, followed by heart, liver, swim bladder, and gill, suggesting that muscle has the highest ability to accumulate Hg compared to the other organs. More importantly, no discernible “reservoir effect” was observed in the TGR within the initial few years after impoundment due to its special eco-environment including: 1) neutral and slightly alkaline pH and low dissolved organic carbon of water, 2) less vegetation coverage in inundated areas, 3) simple food web.

Correlation between δ13C and δ15N in flying fish (Exocoetus volitans) muscle and scales from the South China Sea

Abstract We collected flying fish (Exocoetus volitans) from the South China Sea to determine whether fish scale isotope values correlate with those from muscle, and discuss relevant eco-environmental implications. A significant positive correlation was determined between fish scales and muscle δ13C and δ15N, rendering a fish scale an alternative to muscle tissue for stable isotope analysis. However, muscle and scale isotopic offsets should be fully considered when using δ13C and δ15N to analyze the actual trophic level of fish and their food source. The average offsets of δ13C and δ15N between muscles and scales are -2.1 ± 0.5‰ and 2.3 ± 0.6‰, respectively, though these values vary slightly with fish mass. Weak correlations were found between δ13C and δ15N, both in the flying fish muscle and scales, suggesting that other factors are influencing δ13C and δ15N. Fish δ15N also correlates with the size of individuals, while δ13C reflects the marine habitat. Based on our data, it appears that more eco-environmental processes can be revealed from modern or ancient flying fish scales.

Low lipid and urea effects and inter-tissue comparisons of stable isotope signatures in three nearshore elasmobranchs

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 579:233-238 (2017) - DOI: https://doi.org/10.3354/meps12264 NOTE Low lipid and urea effects and inter-tissue comparisons of stable isotope signatures in three nearshore elasmobranchs Oliver N. Shipley1,2,*, Karen J. Murchie3, Michael G. Frisk1, Edward J. Brooks2, Owen R. O’Shea2, Michael Power4 1School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11790, USA 2Shark Research and Conservation Program, The Cape Eleuthera Institute, Eleuthera, The Bahamas 3Daniel P. Haerther Center for Conservation and Research, John G. Shedd Aquarium, 1200 South Lake Shore Drive, Chicago, IL 60605, USA 4Department of Biology, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada *Corresponding author: oliver.shipley@stonybrook.edu ABSTRACT: Stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) is a common tool used to examine aspects of elasmobranch biology and ecology; however, accurate ecological interpretation of stable isotope values requires knowledge of lipid and urea dynamics, and the variable turnover rates of different tissue types. Here we examined lipid and urea dynamics and inter-tissue comparisons of stable isotope values in 3 nearshore elasmobranch species, the nurse shark Ginglymostoma cirratum, southern stingray Hypanus americanus, and the Atlantic chupare stingray Styracura schmardae. Chemical extraction had no significant effect on δ13C and δ15N values of nurse shark muscle, and southern and chupare stingray fin, suggesting negligible lipid and urea components associated with these tissues. For nurse sharks, δ13C values were higher in muscle compared to dermis and δ15N was lower. The causes of this variability are underpinned by the metabolic variability between tissue types, the physiological function of which remains undetermined. Finally, we observed a significant relationship between muscle and dermis δ13C and δ15N, providing the first inter-tissue isotopic correction for nurse sharks. The results provide insight into lipid and urea dynamics, and aid sample preparation and ecological interpretation of stable isotope data in these taxa. KEY WORDS: Stable isotope analysis · δ13C · δ15N · Elasmobranch · Shark · Stingray · Polar compounds Full text in pdf format Corrigendum PreviousCite this article as: Shipley ON, Murchie KJ, Frisk MG, Brooks EJ, O’Shea OR, Power M (2017) Low lipid and urea effects and inter-tissue comparisons of stable isotope signatures in three nearshore elasmobranchs. Mar Ecol Prog Ser 579:233-238. https://doi.org/10.3354/meps12264 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 579. Online publication date: September 14, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Preliminary assessment of the trophic structure of demersal fish community in the Sea of Oman

Detailed knowledge on the trophic ecology of marine species is an essential asset for the development of appropriate ecosystem-based management of marine fisheries. In the Sea of Oman, no studies to date have addressed the diet of demersal fish inhabiting soft-bottom habitats, despite the importance of these habitats for local fisheries. This study provides a preliminary investigation of feeding strategies displayed by demersal fish communities at two seasons in the Sea of Oman, Muscat waters, based on stomach content and dorsal muscle δ15N, δ13C and δ34S analyses. A total of 46 fishes from 15 species, 14 families and 7 orders were collected in December 2013 and March 2014. All species displayed a carnivorous diet, with variable contributions of invertebrate and fish prey. While stomach content data suggested that Fistularia petimba (Fistulariidae), Saurida tumbil (Synodontidae) and Ulua mentalis (Carangidae) were mostly piscivorous, their δ15N values strongly overlapped with other species found to feed mostly on invertebrates, suggesting a mixed fish-invertebrate feeding on a longer time scale. No significant variations were found between months in terms of mean isotopic values, but larger range values and variances were observed for δ13C and δ34S in December, possibly indicating the consumption of food resources from more diverse mixture and origin during that month. Only δ15N was weakly but significantly related to fish size at the community level, suggesting a poor size-related structuration of the demersal fish community at the spatial and temporal scale examined, consistent with other studies in the study area. However, the low number of samples analyzed limited the scope of our conclusions, and further investigations based on stable isotope methodology are needed to obtain essential biological knowledge for ecosystem-based management of fisheries in the Sea of Oman.

Nonlethal sampling for stable isotope analysis of juvenile Chinese sturgeon (Acipenser sinensis ): Comparing δ13 C and δ15 N signatures in muscle and fin tissues

We compared δ13C and δ15N values of muscle with fin from juvenile Chinese sturgeon (Acipenser sinensis), to evaluate the feasibility of using nonlethal (fin) as an alternative to lethal (muscle) sampling. Size and lipid effect on the relationship between fin and muscle were also investigated. Dorsal muscle (DM) and fin clip (FC) were collected from A. sinensis with different body length (120–373 mm) in the Yangtze Estuary for isotope analysis. The result showed that (1) muscle isotope values could estimated by the values of fin, from either use the regression model (δ13CDM = 0.939 × FC − 2.577; δ15NDM = 0.737 × FC + 4.638) or constants factors (δ13CDM = δ13CFC − 1.27; δ15NDM = δ15NFC + 0.59); (2) no size-based relationships with δ13C and δ15N from either fin or muscle; (3) lipid extraction significantly improving the fin and muscle regression model fit for both δ13C and δ15N values. Therefore, this study support the use of nonlethal fin tissues for isotope analysis of juvenile A. sinensis, and will allow trophic studies to avoid the effect of lipid accumulation from muscle.