Stable Isotope Values Research Articles

Evaporation dominates the loss of plateau lake in Southwest China using water isotope balance assessment

The water balance budget in remote plateau lakes provides a fundamental information on the local climate-hydrological pattern. However, integrated investigation on the waters entering the lake, especially groundwater, was limited. To assess the current climate stress on Yunnan-Guizhou Plateau lakes, we collected rivers, groundwater, lake, and precipitation with varying isotopic compositions in the Chenghai Lake basin over four separate campaigns during a hydrological year. The wide and enriched variation of isotope composition in rivers, groundwater, and lake indicate that they have undergone distinct evaporations, which further reveal the recharging and mixing processes. Based on the similar isotopic signals between rivers and precipitation, rivers can serve as proxies for precipitation. Groundwater was primarily replenished by high mountain precipitation duo to the stable isotopic values in aquifers. Even through mass water in lake was able to smooth out some variability, the considerable isotopic variation of lake during the four collections suggested the influence of meteorological conditions. According to the assessment of isotope balance model, lake evaporation accounts for almost 65 % of the total inflow for one year, which partially explains the climate stress on the lake level. As the most sensitive variables, changes in relative humidity (h) and isotope composition of atmospheric moisture (δA) resulted in remarkable variations in E/I ratios and the constructed water isotope framework. These results shed light on the capacity of evaporation relative to lake input and provide interpretations on local paleoclimate and predicted-climate construction.

New stratigraphic and paleoenvironmental constraints on the Paleogene paleogeography of Western Amazonia

The rise of the Andes and the associated propagation of the retroarc foreland basin during the Mesozoic Cenozoic in western South America shaped the paleogeography and paleoenvironmental settings of Western Amazonia. Much attention has been paid to the Neogene evolution of the Amazonian Basin, but few studies have investigated in detail the paleoenvironments of Western Amazonia during the Paleogene. We present a multi-proxy study that includes new biostratigraphic and paleontologic data, the interpretation of depositional environments and zircon U–Pb data from the Upper Cretaceous-Paleogene sedimentary sequence exposed in the Huallaga Basin (northern Peru). The biostratigraphic dating suggests that the lower part of the sequence is Maastrichtian in age. The maximum depositional age and maximum likelihood age according to the U–Pb zircon dating of Paleogene sedimentary rocks indicate Lutetian to Bartonian ages (from 43.5 ± 0.64 Ma to 37.6 ± 0.85 Ma). These results reveal a hiatus in the depositional record during Paleocene time. Two depositional systems can be distinguished: a lacustrine system composed of red mudrocks interbedded with thick sandstone layers and carbonate beds, and a siliciclastic tide-dominated system composed of fine-to medium-grained sandstones associated with tidal bundles, reactivation surfaces and heterolithic stratifications. However, the carbon and oxygen stable isotope values in carbonates tend to characterize a freshwater system, with a transition to brackish conditions toward the upper part of the section (Bartonian), thereby suggesting the presence of an estuary system. Finally, we suggest that the Bartonian shallow marine incursion recorded in the Huallaga Basin occurred from the north through the Caribbean Sea, and that it might have played a role in regional biodiversity patterns in the Paleogene.

Composition of Chinook salmon faecal wastes with implications for environmental management

Intensive salmon aquaculture is now a major industry globally, with Chinook salmon (Oncorhynchus tshawytscha) the dominant culture species in New Zealand. Understanding the composition of Chinook salmon wastes is important for assessing environmental risks of coastal open-cage aquaculture, both in terms of nutrient inputs, and for evaluating potential characteristics that could be used as fish waste markers in the environment. The aim of our study was to describe the biochemical composition of faecal waste from Chinook salmon with a view to describing the characteristics most important for assessing waste inputs in the environment. A broad suite of biochemical characteristics, including nutrient, mineral and trace element concentrations, bulk carbon and nitrogen stable isotope and compound specific Ᵹ13C fatty acid and amino acid values, were measured during an experiment on fish kept in a recirculating aquaculture system (RAS) and fed a standard commercial pellet diet. We found that all biochemical characteristics of feed were conserved in faecal material, but some were conserved better than others. Fatty acid composition was similar in feed and faeces, but element profiles differed and showed high variability in faeces. Carbon and nitrogen bulk stable isotope values of faecal samples were generally lower than mean feed signatures, particularly for Ᵹ15N. For compound specific stable isotopes, the Ᵹ13C values in most fatty acids were similar to that of feed, however, Ᵹ13C values in amino acids were lower (with the exception of phenylalanine and glutamic acid). Based on our findings, we suggest that it may be possible to predict biochemical composition of faeces for well-conserved, or predictably-altered indicators using composition of feed samples alone. The differences between feed and faeces for some markers (e.g., elements, nutrient ratios, Ᵹ15N and Ᵹ13C in amino acids) may be useful for distinguishing between the presence of these two farm-derived wastes in the environment. Our results also suggest that the elemental composition of Chinook salmon waste is generally similar to that of other salmonid species, and supports the transfer of element composition data from other salmonids when setting mass balance model parameters for Chinook salmon.

Effects of ethanol storage and lipid extraction on stable isotope compositions of twelve pelagic predators

Stable isotope analysis (SIA) has proven to be a powerful tool in reconstructing diets and characterizing trophic relationships for pelagic predators. Ethanol has been a common preservative solution for biopsy samples from remote areas and archived collections. It is still under debate whether the effects of ethanol (ET) would bias the trophic interpretation of the stable isotope values. Further, lipid extraction (LE) is becoming more popular as a general treatment for standardization prior to SIA, particularly for investigating intra and interspecific variation of sympatric species, because lipids have lower δ13C values. In this study, the long-term (up to 448 days) effects of treatment ET and combined treatments ET and LE (ET+LE) on stable carbon and nitrogen isotope values (δ13C and δ15N, respectively) of twelve pelagic predators from the open ocean were evaluated. Results showed that compared with control values, δ15N values displayed a positive change (δ15Nmean offset was 0.71 ± 0.56‰) but δ13C values had variable results (δ13Cmean offset was 0.42 ± 0.64‰) among all species following treatment with ET during the first 28 days and then remained stable throughout the experiment. Compared with treatment LE results, no difference was observed in δ13C, δ15N values, and C/N ratios through time following treatment ET+LE. These results indicated that treatment ET may have species-specific effects on stable isotope values, and the shifts from treatment LE could counter the changes caused by treatment ET. In addition, after 28 days of preservation, the values following treatment ET were similar to those following treatment LE in low C/N species (C/N<3.5), which suggested ethanol may also affect some of lipid contents from muscle tissues. Nevertheless, further research is needed to focus on the mechanisms that control changes in stable isotope composition in tissues stored in ethanol. Given the effects on pelagic predators, muscle tissue samples stored in ethanol from the open ocean or a museum after LE treatment could be used to develop SIA.

Paired Synoptic and Long-Term Monitoring Datasets Reveal Decadal Shifts in Suspended Sediment Supply and Particulate Organic Matter Sources in a River-Estuarine System

The San Francisco Estuary, in central California, has several long-running monitoring programs that have been used to reveal human-induced changes throughout the estuary in the last century. Here, we pair synoptic records of particulate organic matter (POM) composition from 1990–1996 and 2007–2016 with more robust long-term monitoring program records of total suspended sediment (TSS) concentrations generally starting in the mid-1970s to better understand how POM and TSS sources and transport have shifted. Specifically, POM C:N ratios and stable isotope values were used as indicators of POM source and to separate the bulk POC pool into detrital and phytoplankton components. We found that TSS and POC sources have shifted significantly across the estuary in time and space from declines in terrestrial inputs. Landward freshwater and brackish water sites, in the Delta and near Suisun Bay, witnessed long-term declines in TSS (32 to 52%), while seaward sites, near San Pablo Bay, recorded recent increases in TSS (16 to 121%) that began to trend downwards at the end of the record considered. Bulk POM C:N ratios shifted coeval with the TSS concentration changes at nearly all sites, with mean declines of 12 to 27% between 1990–1996 and 2007–2016. The widespread declines in bulk POM C:N ratios and inferred changes in POC concentrations from TSS trends, along with the substantial declines in upstream TSS supply through time (56%), suggest measurable reductions in terrestrial inputs to the system. Changes in terrestrial TSS and POM inputs have implications for biotic (e.g., food web dynamics) and abiotic organic matter cycling (e.g., burial, export) along the estuarine continuum. This work demonstrates how human-generated environmental changes can propagate spatially and temporally through a large river-estuary system. More broadly, we show how underutilized monitoring program datasets can be paired with existing (and often imperfect) synoptic records to generate new system insight in lieu of new data collection.

Leaf functional traits have more contributions than climate to the variations of leaf stable carbon isotope of different plant functional types on the eastern Qinghai–Tibetan Plateau

Elucidating the mechanisms that control the leaf stable carbon isotope values (δ13Cleaf) is the prerequisite for the widespread application of δ13Cleaf. However, the competing effects of physiological and environmental factors on δ13Cleaf variations of the different plant functional types (PFTs) have not been disentangled, and the corresponding mechanisms remain unclear. Based on large-scale δ13Cleaf measurements on the eastern Qinghai–Tibetan Plateau, the relative contributions and regulatory pathways of leaf functional traits (LFTs) and climatic factors to δ13Cleaf variations of the different PFTs were investigated. We found that δ13Cleaf of the different PFTs was correlated with annual mean precipitation negatively, but not a simple linear relationship with annual mean temperature and varied by PFTs. Leaf nitrogen content per unit area and leaf mass per area (correlated with δ13Cleaf positively) had more substantial effects on the δ13Cleaf variations of the different PFTs than other LFTs. The relative contributions of LFTs to the δ13Cleaf variations were greater than that of climatic factors, and the direct and indirect effects of climatic factors on δ13Cleaf variations varied by PFTs. Our findings provide new insights into understanding key drivers of δ13Cleaf variations at the PFT level on a regional scale.

Paired stable carbon and oxygen isotope analyses of human enamel for forensic human geolocation: An exploratory study

Stable carbon isotope analysis has proven utility for reconstructing dietary information in humans in past populations. The usefulness of stable carbon for forensic geolocation has been little investigated, largely because of the globalization of the human diet seemingly rendering it inconsequential. This study queried this assumption at a country-wide level on a known sample group. Stable carbon isotope values were obtained from human enamel with known biographical and geographical information to determine whether stable carbon, when paired with stable oxygen isotope values, could differentiate Canadians from non-Canadians. Samples originating outside of Canada were separated into three regions, and a linear discriminant analysis was used to generate discriminant functions that best separate the regions according to the stable carbon and oxygen isotope values. The results revealed two functions, where the first function explained 92.1% and the second 7.9% of the variance. Although some overlap in stable carbon and oxygen values was observed for individuals from both the United States and Canada, differences were observed between those from Canada and other geographical regions. This study demonstrated that pairing the dietary isotope carbon with the geolocator stable oxygen isotope, produced an interesting separation geographically, one that might well be helpful when attempting a geolocation query on unknown human remains.

Estimating the influence of carbonates in the stable isotopic values of suspended particulate organic matter: implications in ecological studies

Estimating the influence of carbonates in the stable isotopic values of suspended particulate organic matter: implications in ecological studies

Effects of tissue decomposition on stable isotope ratios and implications for use of stranded animals in research

AbstractStable isotope analysis (SIA) provides ecological data that can be safely and efficiently collected on endangered, threatened, and cryptic species. Marine mammals are an ecologically important group for which economical and logistical constraints can make data collection challenging. Stranded marine mammals are often used in research, but the causes of strandings and subsequent tissue decomposition could affect SIA. We conducted a three‐part study to test the validity of using δ13C and δ15N values from tissues of stranded bottlenose dolphins (Tursiops truncatus) and West Indian manatees (Trichechus manatus) for ecological studies. First, we quantified isotopic overlap using ellipses based on 95% of the data to compare isotope values in skin between stranded and live‐captured animals. Second, we compared stable isotope values from liver, skin, and muscle of animals that had stranded and were sampled at different decomposition stages. Third, we experimentally exposed each tissue to environmental conditions and sampled tissues as they decomposed. For both dolphins and manatees, isotopic ellipses from skin of stranded carcasses were similar to live‐captured individuals. Among individuals recovered at different decomposition stages, more advanced decomposition affected δ13C values in dolphin liver and skin but not in manatee tissues and had no effect on δ15N values in any tissue for either species. In the experimental manipulation, decomposition resulted in depleted δ13C values, enriched δ15N values, and increased C:N in liver for both species. Skin and muscle from stranded dolphins and manatees are representative of their corresponding live populations and can be used for SIA with appropriate caution. To facilitate the use of tissues from stranded animals, tissues should be dried or frozen for storage as soon as possible after sampling. We recommend liver from stranded animals only be used for SIA when researchers need tissues with short turnover times and can access fresh samples. Without consideration of decomposition effects on isotope values, ecologists may make inaccurate inferences about habitat use, diet, and community structure. Careful use of SIA on tissues from stranded animals can help researchers provide better quality information for managers and policy makers.

Deciphering the complex trophic relationship of the black-spotted croaker (Teleostei: Sciaenidae) and its parasites using stable isotope analysis

The stable isotope values of nitrogen (δ15N) and carbon (δ13C) have been widely used in ecological studies to decipher the trophic relationships and interactions that occur between living organisms. The aim of this study was to determine the trophic relationship between a commercially important tropical Australian marine fish ( Protonibea diacanthus (Lacepède, 1802)) (Sciaenidae) and its associated parasites, through stable isotope analysis of nitrogen and carbon (δ15N and δ13C). We examined the stable isotope ecology of four parasitic organisms: adult ectoparasitic copepods, and endoparasitic adult digeneans and nematodes and plerocercoids. Nitrogen in endoparasites was consistently depleted when compared with the host; however, digeneans expressed nitrogen signatures almost equivalent to those of the host. Ectoparasitic copepods were the only parasite that was substantially enriched in nitrogen compared with the host. All adult parasitic organisms were carbon depleted when compared with the host tissue associated with the site of infection; however, plerocercoids were enriched. Our findings emphasize the complexity of parasite–host interactions and the varying values of isotopic discrimination between parasite type, life-cycle stage, and location in host.

Sequential analysis of δ15 N in guard hair suggests late gestation is the most critical period for muskox calf recruitment.

Analysis of stable isotopes in tissue and excreta may provide information about animal diets and their nutritional state. As body condition may have a major influence on reproduction, linking stable isotope values to animal demographic rates may help unravel the drivers behind animal population dynamics. We performed sequential analysis of δ15 N values in guard hair from 21 muskoxen (Ovibos moschatus) from Zackenberg in high arctic Greenland. We were able to reconstruct the dietary history for the population over a 5-year period with contrasting environmental conditions. We examined the linkage between guard hair δ15 N values in 12 three-month periods and muskox calf recruitment to detect critical periods for muskox reproduction. Finally, we conducted similar analyses of the correlation between environmental conditions (snow depth and air temperature) and calf recruitment. δ15 N values exhibited a clear seasonal pattern with high levels in summer and low levels in winter. However, large inter-annual variation was found in winter values, suggesting varying levels of catabolism depending on snow conditions. In particular δ15 N values during January-March were linked to muskox recruitment rates, with higher values coinciding with lower calf recruitment. δ15 N values were a better predictor of muskox recruitment rates than environmental conditions. Although environmental conditions may ultimately determine the dietary δ15 N signal in muskox guard hairs, muskox calf recruitment was more strongly correlated with δ15 N values than ambient snow and temperature. The period January-March, corresponding to late gestation, appears particularly critical for muskox reproduction.

Predicting spatial distribution of stable isotopes in precipitation by classical geostatistical- and machine learning methods

Stable isotopes of precipitation are important natural tracers in hydrology, ecology, and forensics. The spatially explicit predictions of oxygen and hydrogen isotopes in precipitation are obtained through different interpolation techniques. In the present study we aim to examine the performance of various interpolation techniques when predicting the spatial distribution of precipitation stable isotopes. The efficiency of combined geostatistical tools (i.e. regression kriging; RK) and various machine learning methods (including regression enhanced random forest methods: MRRF, RERF) are compared in interpolating the spatial variability of precipitation stable oxygen isotope values from two different sampling networks in Europe. To assess the performance of the models, mean squared error (MSE), nonparametric Kling Gupta efficiency (KGE), absolute differences and relative mean absolute error metrics were employed. It was found that the combination of the different regression techniques with Random Forest can produce estimations with comparable accuracy in terms of descending order of overall average MSE, MRRF: 2.61, RK: 2.77, RERF: 2.99, RF: 3.08. The best performing combined random forest model variant (MRRF) outperformed regression kriging in terms of a hybrid error metric (KGE) by 7.5%. Sequential random rarefying the station networks showed that machine-learning methods are more capable of maintaining high prediction accuracy even with fewer input data. This can be a great advantage when a suitable method is needed to predict the stable isotope composition of precipitation for large spatial domains where the spatial density of data stations shows large differences.

RECONSTRUCTING KUNGURIAN (CISURALIAN, PERMIAN) TERRESTRIAL ENVIRONMENTS WITHIN A MEGACALDERA IN THE SOUTHERN ALPS (N-ITALY) USING LITHOFACIES ANALYSIS, PALYNOLOGY AND STABLE CARBON ISOTOPES

During the Permian, climate experienced a change from icehouse to greenhouse conditions. Few multidisciplinary studies have investigated Kungurian (late Cisuralian) tropical terrestrial ecosystem and climate changes. Here, we apply an interdisciplinary approach to two alluvial-lacustrine successions of the Athesian Volcanic Group (Southern Alps, northern Italy) deposited in a Kungurian megacaldera during periods of volcanic quiescence. Sedimentological analysis combined with palynofacies studies allowed the reconstruction of the depositional environments. The study of sporomorph assemblages and stable organic carbon isotopes provided information on plant communities and the climate context. Two different depositional environments were present in the megacaldera: one proximal and one more distal with respect to the source, distinguished by a slightly different composition of the sediments, palynofacies and organic carbon isotopes. The plant community in the area was dominated by xeromorphic-hygromorphic taxa. The δ13Corgvalues are comparable to those of other Cisuralian continental organic matter and plants. The stable carbon isotope values show a small variability, which correlates weakly, but significantly, with the abundance of xeromorphic elements. All observations support deposition during semiarid to arid climate conditions, typical of the mid-late Cisuralian in the area.

Trophic position variability of European sardine by compound-specific stable isotope analyses

The study of the trophic position (TP) of organisms is crucial to understand the trophodynamics of ecosystems. The European sardine from the western Mediterranean has been highly exploited during the last decades and has shown an important population decline. To determine the TP, we quantified seasonal nitrogen stable isotope (δ15N) values of compound-specific stable isotope analysis of amino acids (CSIA-AA), as well as bulk δ15N (SIA-bulk) values in muscle from three areas of the north-western Mediterranean. Our results highlight that, despite observing latitudinal changes in nitrogen SIA-bulk, the TP of sardine remains similar between sites. These results suggest that changes in nitrogen SIA-bulk are mainly driven by changes in the isotopic ratio of the baseline. Furthermore, the seasonal nitrogen variation in SIA-bulk is linked to differences in the isotopic baseline of the pelagic food web observed in the source AAs. Using CSIA-AA allowed us to decouple the variation in the baseline from the trophic variation producing robust TP estimates. Without using CSIA-AA, the interpretation of nitrogen SIA-bulk was hampered by the lack of a proper regional baseline of the primary producers.

Evaluating food metrics of lanternfishes in waters of the southeastern Pacific Ocean

Using carbon and nitrogen stable isotope values, we analyzed the trophic position (TP) and the isotopic niche width of lanternfishes from three different areas in the Southern Pacific Ocean. Fishes from Perú had slightly higher δ13C values compared with fish from Chilean areas. In contrast, δ15N values increased with latitude (North to South). Myctophids TP differed between the three study areas (highest in Central Chile, lowest in Peru). Peruvian fishes had a smaller isotopic niche than the lanternfishes of those from Chile.

Sedimentary Accumulation of Black Carbon on the East Coast of The United States

AbstractThe occurrence, trends and sources of soot black carbon (BC) in coastal sediments are poorly understood, particularly during the Anthropocene. Two sediment cores, covering the last ∼100 years from the US East Coast, off North Carolina and in the Florida Straits, were analyzed for organic carbon (OC), BC fluxes and BC sources. BC fluxes were 0.1 g cm−2 year−1 at both sites and accounted for 8%–22% of total OC. Carbon stable isotope values indicated OC to be of marine origin, while the BC was mostly terrestrially derived, C3‐plant material. Radiocarbon values revealed BC originating mostly from fossil fuels or pre‐aged carbon (fraction modern of 14%–31%) at North Carolina, while in the Florida Strait the BC was mostly derived from biomass burning (fraction modern of 70%–74%), in‐line with continental (NC) or marine (FS) air mass origins. Ratios of polycyclic aromatic hydrocarbons broadly supported different BC sources at the two sites.

Non-breeding behaviour in the Brown Skua (Stercorarius antarcticus lonnbergi): insights from modelling moulting patterns and stable isotope analyses

ABSTRACT Long-term changes in the life history and behaviour of seabirds during the non-breeding season can reflect shifts in environmental conditions. However, long-term marine studies are scarce, particularly on southern hemisphere seabirds. Here, we used moult scores from 86 Brown Skuas (Stercorarius antarcticus lonnbergi), a large predatory seabird breeding on the Chatham Islands, Aotearoa/New Zealand to model both the timing and duration of primary feather moult. In addition, we analysed stable isotope values (δ13C and δ15N) from 62 modern (2014–16) and ten museum tail feathers. These data provide insights into the non-breeding behaviour of Brown Skua. Interestingly, our results show that the primary feather moult occurred prior to birds departing the colony, starting on average on 2 January ± 5 days (SE). The average start of primary feather moult occurred five days prior to the end of breeding (7 January ± 10 days (SD)) and 42 days before the birds departed the colony (13 February ± 11 days (SD)). The average duration of primary feather moult was 189 ± 14 days (SE). Importantly, low δ13C values in four females suggested that tail feather moult might also occur while skuas are at the colony. There was no difference in tail feather δ13C and δ15N values between any pairwise comparison of modern and museum years. However, values of δ15N from tail feathers sampled in 2014 were different from those sampled in 2015 and 2016. This large annual variation in δ15N values from tail feathers over such a short period makes long-term comparisons difficult to interpret, particularly between years with low sample sizes. While the stable isotope analyses of tail feathers are informative, we recommend future studies of skuas sample the primary coverts rather than tail feathers.

Feeding ecology of coexisting Heermann’s gull (Larus heermanni) and elegant tern (Thalasseus elegans) chicks, based on stable isotope measurements

The Heermann’s gull and the elegant tern are considered Near Threatened by the IUCN Red List of Threatened Species and under special protection under Mexican environmental law. Close to 95% of the world populations of both species breed on Isla Rasa (Gulf of California). As both species breed on the same island, competition for trophic resources can be expected to be high. Here, the feeding ecology of chicks of both species, as well as the contribution by prey species provided by adults, was studied using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis in 3 consecutive breeding seasons (2017, 2018, and 2019). Results of the stable isotope analysis revealed that although some segregation in the δ13C and δ15N values exists between both species, isotopic mixing model outputs indicated that fishes were the most important prey group for both. However, at the prey species level, the most important prey consumed by Heermann’s gulls were northern anchovy, Pacific sardine, and Pacific mackerel, followed by pelagic crab, whereas elegant terns consumed mainly northern anchovy. The trophic width estimated with the stable isotope values during 2017 and 2019 was higher for the Heermann’s gull than for the elegant tern. In contrast, for 2018, the trophic width of the elegant tern was higher than that of the Heermann’s gull. In addition, both species showed a high degree of trophic width overlap during 2017 and 2019 (overlap probability 0.67 and 0.79, respectively). These results highlight the ability of the Heermann’s gull to redirect its food intake to what might be the most accessible prey groups, a feeding strategy that allows the coexistence.

Comparisons of morphometrics and body condition between two breeding populations of Australian humpback whales

Context The east and west coasts of Australia form the breeding grounds for two of the world’s largest and fastest-growing populations of humpback whales (Megaptera novaeangliae). These populations show differences in mean lipid content, fatty acid profiles, and stable isotope values. Aims To determine whether these differences result in variation in nutritional health and physiology between populations, we quantified and compared the morphology, body condition and energetic requirements between the two populations. Methods We used unmanned aerial vehicles to measure body morphometrics (residual of body volume vs length) of humpback whales from May to November in 2017, 2020 and 2021. Key results Morphometric measurements were obtained from 973 humpback whales (119 calves, 249 juveniles, 486 adults, and 119 lactating females). Results showed that the two populations did not differ significantly in their morphology. The average body condition was significantly different for sexually mature reproductive classes, with adults and lactating females on the west coast having a lower body condition, by an average of 7.7 and 11.1 percentage points below the east coast population respectively. All reproductive classes, with the exception of calves followed a similar pattern in body condition loss through the breeding season. Calves on the east coast exhibited a curvilinear relationship with days post-partum, with early and late-migrating calves being in poorer body condition than were those migrating mid-season. In contrast, west coast calves did not significantly change their condition through the breeding season. Conclusions The poorer body condition of sexually mature individuals in the west coast population is concerning, given the overall condition loss during a breeding season. This difference could be influenced by variations in sampling time; however, differences in feeding opportunities, climatic regimes and/or environmental variables may influence the ability of one population to acquire similar amounts of energy. Implications The difference in body condition between these two humpback whale populations highlighted the need to assess populations individually, so as to develop representative levels that can be used for future conservation monitoring and management.

Estimating trophic guilds based on isotopic niches of demersal fishes, squids and crustaceans in the East China Sea

Context Identifying trophic guilds, i.e. species groups having similar trophic niches, is a first step in effective stock and fisheries management with consideration of multiple species interactions or ecosystems. Aims We evaluated isotopic niches by using stable isotope values (δ13C and δ15N) for 53 species, including commercially important demersal fishes, squids and crustaceans, from the continental shelf to the slope of the East China Sea (ECS), to segregate these species into guilds. Methods We inferred the isotopic niche space of each species and community metrics for guilds using Bayesian statistics. Key results Values of δ13C and δ15N showed different isotopic niches among species, reflecting a range of trophic positions and baseline food sources. The 53 species were segregated into 12 guilds on the basis of isotopic niche overlaps. Niche size and evenness differed among guilds; half of the guilds had smaller and less diverse niches than did the others. Conclusions The guilds identified for ECS demersal biota reflected similarities of taxonomy, behaviour, habitat and feeding type; niche size and evenness within each guild might have been influenced by the degree of species interaction. Implications These results provide important ecological information for considering effective multi-species management.