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Patterns of feeding and growth of Atlantic salmon Salmo salar L. in the marine environment are critical to understanding how observed declines in recruitment may reflect warming or other oceanic drivers. The isotopic composition of scales can provide insight into differences in marine feeding location and possibly temperature regime. The authors used archived scale samples to measure δ13C and δ15N deposited in the scales of one sea‐winter (1SW) salmon during their last season of growth at sea before they returned to five Irish rivers. δ13C values were related statistically to observed salmon body condition (Fulton's K), and fish with higher δ13C values tended to show significantly better condition. In contrast, δ15N values were negatively related to body condition. There was no important effect on condition of length at smolt migration, and the effect of duration of marine residence varied among rivers. It is likely that δ13C values partly reflected ambient ocean temperature and recent marine feeding environment before return migration, such that the observed relationship between higher δ13C values and increased body condition may express an advantage for adult fish feeding in warmer, potentially closer, waters. If greater body condition influences fitness, then a changing temperature regime in the Northeast Atlantic may drive shifts in salmon survival and reproduction. This study provides evidence that there is spatial and trophic variation at sea between salmon from rivers of origin that are located relatively close to each other, with potential consequences for body condition and, consequently, fitness and life history; this suggests that salmon populations from geographically proximate rivers within regions may exhibit differential responses to ocean‐scale climatic changes across the Northeast Atlantic. [ABSTRACT FROM AUTHOR]

Seasonal differences in the availability of resources potentially result in the food web architecture also varying through time. Stable isotope analyses are a logistically simple but powerful tool for inferring trophic interactions and food web structure, but relatively few studies quantify seasonal variations in the food web structure or nutrient flux across multiple trophic levels. We determined the temporal dynamics in stable isotope compositions (carbon, nitrogen and sulphur) of a fish community from a highly seasonal, temperate estuary sampled monthly over a full annual cycle. Sulphur isotope values in fish tissues discriminated among consumers exploiting pelagic and benthic resources but showed no seasonal variation. This implied limited change in the relative consumption of pelagic and benthic resources by the fish community over the study period despite major seasonal changes in phytoplankton biomass. Conversely, carbon and nitrogen isotope values exhibited seasonality marked by the commencement of the spring phytoplankton bloom and peak chlorophyll concentration, with δ13C values following expected trends in phytoplankton growth physiology and variation in δ15N values coinciding with changes in major nitrogen sources to plankton between nitrate and ammonium. Isotope shifts in fish muscle were detected within 2 weeks of the peak spring phytoplankton bloom, suggesting a rapid trophic transfer of carbon and nitrogen along food chains within the estuarine food web during periods of high production. Therefore we caution against the assumption that temporal averaging effectively dampens isotopic variability in tissues of higher trophic‐level animals in highly dynamic ecosystems, such as temperate estuaries. This work highlights how stable isotope analyses can be combined with environmental data to gain a broader understanding of ecosystem functioning, while emphasising the need for temporally appropriate sampling in stable isotope‐based studies. [ABSTRACT FROM AUTHOR]

Ensuring sustainability of the world fisheries is a key conservation and economic objective. Traceability of seafood from the final sale back to the point of harvest is an important aspect, supporting both fishery management and consumer protection. Stable isotope-based geolocation can be applied to trace the spatial origin of seafood, drawing on comparisons between the isotopic compositions of the product and those of a reference dataset from known spatial locations. This study tests the extent to which stable isotope-based geolocation can be applied to identify catch location of the Norwegian lobster Nephrops norvegicus. Carbon, nitrogen, and sulfur isoscapes across UK shelf seas are used as the reference dataset and test the accuracy of assignment estimates using a variety of bivariate and multivariate stable isotope geolocation approaches. Two alternative Bayesian inversions, one balanced and one weighted, are applied to the outcomes of the statistical models to determine the most accurate methods of assignment. Of all the methods trialed, the multivariate approach using carbon, nitrogen, and sulfur isoscape data produced the most accurate assignments, with c. 60% of samples from each site correctly assigned among six possible fishery origins. Weighted Bayesian approaches resulted in more correct assignments to highly fished sites, but at a cost of reduced correct assignments to sites of low fishing activity. Processed Nephrops samples obtained from supermarkets were assigned to potential fishery location, with results indicating the majority were captured in the west of Scotland. The isoscape methods explored can be calibrated to any marine feeding organism and provide a useful tool for more efficient management of marine stocks. KEY WORDS: Norway lobster, Nephrops norvegicus, assignment, eco-labeling fisheries, forensics, provenance, seafood management, shellfish, stable isotope ratios, INTRODUCTION In recent years, consumer demand for seafood has risen considerably. In 2008, the average annual per capita consumption of seafood was 17.1 kg (FAO 2012), a value that had [...]

Animal movements and resource utilization are essential factors for effective environmental management, but they are difficult to quantify in extensive natural ecosystems such as the aquatic environment.Stable isotope analysis is an ecological tracer technique that reveals information about links between trophic levels, movement patterns of migratory species or geographical variations due to the different aquatic processes that influence them. The Caspian kutum is an important commercial endemic species on the southern coasts of the Caspian Sea and can be used as a proxy to gain information on how different spatiotemporal, environmental and biological—variables can influence ecological tracers such as stable isotopes at the sea basin level. Thus, the main objective of this study is to investigate how spatiotemporal, isotopic baseline and environmental factors influence the distribution of stable isotopes in the Caspian kutum.The results showed that although there are individual variations, there is an overall increasing trend in δ13C and a decreasing trend in δ15N from the western to the eastern regions. In addition, there is a decreasing trend in δ13C and an increasing trend in δ15N with increasing age. It seems that among other migration routes of this species from the northern part of the southern Caspian Sea to the southern coasts, one of the main migration routes of this fish on the coasts of Iran is west‐east mobility, which may affect the efficiency of sustainable management of the catch in various fishing areas.This was the first study to establish a migratory pattern of the Caspian kutum based on stable isotopes. We advocate the wider stable isotopes to effectively investigate fish migratory, as the results from this study provided important contributions to the development of valuable insights for the management and sustainability for this threatened and declining species fish populations. [ABSTRACT FROM AUTHOR]

Accurate age estimates are crucial for assessing the life‐histories of fish and providing management advice, but validation studies are rare for many species. We corroborated age estimates with annual cycles of oxygen isotopes (δ18O) in otoliths of 86 northern pike (Esox lucius) from the southern Baltic Sea, compared results with visual age estimates from scales and otoliths, and assessed bias introduced by different age‐estimation structures on von Bertalanffy growth models and age‐structured population models. Age estimates from otoliths were accurate, while age estimates from scales significantly underestimated the age of pike older than 6 years compared to the corroborated reference age. Asymptotic length (L∞) was larger, and the growth coefficient k was lower for scale ages than for corroborated age and otolith age estimates. Consequentially, scale‐informed population models overestimated maximum sustainable yield (MSY), biomass at MSY (BMSY), relative frequency of trophy fish (≥100cm), and optimal minimum length limit but underestimated fishing mortality at MSY (FMSY). Using scale‐based ages to inform management regulations for pike may therefore result in conservative management and lost yield. The overestimated asymptotic length may instill unrealistic expectations of trophy potential in recreational anglers targeting large pike, while the overestimation in MSY would cause unrealistic expectations of yield potential in commercial fishers. [ABSTRACT FROM AUTHOR]