Movement and population dispersal of dolphinfish (Coryphaena hippurus) across the Eastern Tropical Pacific inferred from carbon and nitrogen stable isotope analyses.

The dolphinfish (Coryphaena hippurus) is a globally distributed marine predator that supports one of the most important coastal fisheries along the Eastern Tropical Pacific (ETP), but its spatial movements in this area are poorly understood. Stable isotope values (δ13 C and δ15 N) of white muscle from dolphinfish (n = 220) captured at different locations across the ETP (i.e., Mexico, Costa Rica, Ecuador, Peru and oceanic areas) were normalized to copepod baseline stable isotope values to estimate dolphinfish trophic position, movements and population dispersal. Movement or residence patterns were inferred from the difference in δ15 N values (Δ15 Ndolphinfish-copepod ‰) between copepods and dolphinfish muscle. Baseline corrected isotope values (δ13 Cdolphinfish-copepod and δ15 Ndolphinfish-copepod ) of dolphinfish muscle were used to estimate isotopic niche metrics and infer population dispersal across isoscapes. Values of δ13 C and δ15 N differed between juvenile and adult dolphinfish and across the ETP. Trophic position estimates ranged from 3.1 to 6.0 with a mean of 4.6. Adults and juveniles had similar trophic position estimates, whereas isotopic niche areas (SEA ‰2 ) of adults were greater relative to juveniles in every location. Adult dolphinfish showed "moderate movement by some individuals" in all locations based on Δ15 Ndolphinfish-copepod values, except for Costa Rica where adults were classified with "high degree of movement by some individuals" whereas juveniles showed "limited movement" in all areas except Mexico. Population dispersal based on Δ15 Ndolphinfish-copepod values showed "moderate" and "high" dispersal for adults and "no dispersal" for most juveniles, except for Mexico. This study provides insight into potential dolphinfish spatial mobility across an area of interest for multiple nations, which can help to improve stock assessments and management of the species.

Broadbill swordfish (Xiphias gladius) foraging and vertical movements in the north-west Atlantic.

The northern edge of Georges Bank is an important seasonal foraging habitat for swordfish (Xiphias gladius) in the North Atlantic, where aggregations support commercial pelagic longline and harpoon fisheries. Following a period of overfishing during the 1990s, the North Atlantic X. gladius stock underwent a period of recovery during the early 2000s and was considered rebuilt in 2009. We analysed stomach contents from X. gladius (n = 39) harvested by the Canadian harpoon fishery on Georges Bank in 2007 to characterize diet in this important foraging habitat. We used electronic tagging data from X. gladius (n = 6) on Georges Bank in 2005-2007 to assess vertical habitat preferences and associated prey composition within those zones. We also used stable isotope analysis (δ13 C and δ15 N) of X. gladius liver (n = 2) and common prey types (Paralepididae, Myctophidae, Merluccidae, Ommastrephidae) as a longer-term record of feeding. Stomach contents were co-dominated by Paralepididae [31.9% weight (W)] and Ommastrephidae (36.8%W) with secondary contributions from hake (Merluccidae, 6.5%W), Myctophidae (2.9%W) and Sebastidae (2.1%W). X. gladius displayed diel vertical migrations, descending to depths of 300-400 m during daytime followed by residence in surface waters at night. X. gladius liver δ15 N values were similar to or lower than values of primary stomach contents, likely due to bias of diet consumed in southerly waters with lower nitrogen isotope baselines prior to arrival on Georges Bank. Diet data are similar to results from historical studies from the late 1950s to the early 1980s. This apparent temporal stability to the underlying food web in this region may explain the high X. gladius site fidelity observed in electronic tagging studies and the consistent aggregation of these fish to this region.

Global data set for nitrogen and carbon stable isotopes of tunas.

Nitrogen and carbon stable isotope data sets are commonly used to assess complex population to ecosystem responses to natural or anthropogenic changes at regional to global spatial scales, and monthly to decadal timescales. Measured in the tissues of consumers, nitrogen isotopes (δ15 N) are primarily used to estimate trophic position while carbon isotopes (δ13 C) describe habitat associations and feeding pathways. Models of both δ15 N and δ13 C values and their associated variance can be used to estimate likely dietary contributions and niche width and provide inferences about consumer movement and migration. Stable isotope data have added utility when used in combination with other empirical data sets (e.g., stomach content, movement tracking, bioregionalization, contaminant, or fisheries data) and are increasingly relied upon in food web and ecosystem models. While numerous regional studies publish tables of mean δ15 N and δ13 C values, limited individual records have been made available for wider use. Such a deficiency has impeded full utility of the data, which otherwise would facilitate identification of macroscale patterns. The data provided here consist of 4,498 records of individuals of three tuna species, Thunnus alalunga, T. obesus, and T. albacares sampled from all major ocean basins from 2000 to 2015. For each individual tuna, we provide a record of the following: species name, sampling date, sampling location, tuna length, muscle bulk and baseline corrected δ15 N values, and muscle bulk and, where available, lipid corrected δ13 C values. We provide these individual records to support comparative studies and more robust modeling projects seeking to improve understanding of complex marine ecosystem dynamics and their responses to a changing environment. There are no copyright restrictions for research and/or teaching purposes. Users are requested to acknowledge their use of the data in publications, research proposals, websites, and other outlets following the citation instructions in Class III, Section B.

Trends in tuna carbon isotopes suggest global changes in pelagic phytoplankton communities.

Considerable uncertainty remains over how increasing atmospheric CO2 and anthropogenic climate changes are affecting open-ocean marine ecosystems from phytoplankton to top predators. Biological time series data are thus urgently needed for the world's oceans. Here, we use the carbon stable isotope composition of tuna to provide a first insight into the existence of global trends in complex ecosystem dynamics and changes in the oceanic carbon cycle. From 2000 to 2015, considerable declines in δ13 C values of 0.8‰-2.5‰ were observed across three tuna species sampled globally, with more substantial changes in the Pacific Ocean compared to the Atlantic and Indian Oceans. Tuna recorded not only the Suess effect, that is, fossil fuel-derived and isotopically light carbon being incorporated into marine ecosystems, but also recorded profound changes at the base of marine food webs. We suggest a global shift in phytoplankton community structure, for example, a reduction in 13 C-rich phytoplankton such as diatoms, and/or a change in phytoplankton physiology during this period, although this does not rule out other concomitant changes at higher levels in the food webs. Our study establishes tuna δ13 C values as a candidate essential ocean variable to assess complex ecosystem responses to climate change at regional to global scales and over decadal timescales. Finally, this time series will be invaluable in calibrating and validating global earth system models to project changes in marine biota.

Correction: Author contributions to ecological publications: What does it mean to be an author in modern ecological research?

[This corrects the article DOI: 10.1371/journal.pone.0179956.].

Author contributions to ecological publications: What does it mean to be an author in modern ecological research?

Authorship is a central element of scientific research carrying a variety of rewards and responsibilities, and while various guidelines exist, actual author contributions are often ambiguous. Inconsistent or limited contributions threaten to devalue authorship as intellectual currency and diminish authors' responsibility for published content. Researchers have assessed author contributions in the medical literature and other research fields, but similar data for the field of ecological research are lacking. Authorship practices in ecological research are broadly representative of a variety of fields due to the cross-disciplinary nature of collaborations in ecological studies. To better understand author contributions to current research, we distributed a survey regarding co-author contributions to a random selection of 996 lead authors of manuscripts published in ecological journals in 2010. We obtained useable responses from 45% of surveyed authors. Reported lead author contributions in ecological research studies consistently included conception of the project idea, data collection, analysis, and writing. Middle and last author contributions instead showed a high level of individual variability. Lead authorship in ecology is well defined while secondary authorship is more ambiguous. Nearly half (48%) of all studies included in our survey had some level of non-compliance with Ecological Society of America (ESA) authorship guidelines and the majority of studies (78%) contained at least one co-author that did not meet International Committee of Medical Journal Editors (ICMJE) requirements. Incidence of non-compliance varied with lead author occupation and author position. The probability of a study including an author that was non-compliant with ESA guidelines was lowest for professor-led studies and highest for graduate student and post doctoral researcher-led studies. Among studies with > two co-authors, all lead authors met ESA guidelines and only 2% failed to meet ICMJE requirements. Middle (24% ESA, 63% ICMJE) and last (37% ESA, 60% ICMJE) authors had higher rates of non-compliance. The probability of a study containing a co-author that did not meet ESA or ICMJE requirements increased significantly with the number of co-authors per study although even studies with only two co-authors had a high probability of non-compliance of approximately 60% (ICMJE) and 15 to 40% (ESA). Given the variable and often limited contributions of authors in our survey and past studies of other research disciplines, institutions, journals, and scientific societies need to implement new approaches to instill meaning in authorship status. A byline approach may not alter author contributions but would better define individual contributions and reduce existing ambiguity regarding the meaning of authorship in modern ecological research.

Lipid corrections in carbon and nitrogen stable isotope analyses: comparison of chemical extraction and modelling methods.

1. Lipids have more negative delta(13)C values relative to other major biochemical compounds in plant and animal tissues. Although variable lipid content in biological tissues alters results and conclusions of delta(13)C analyses in aquatic food web and migration studies, no standard correction protocol exists. 2. We compared chemical extraction and mathematical correction methods for freshwater and marine fishes and aquatic invertebrates to better understand impacts of correction approaches on carbon (delta(13)C) and nitrogen (delta(15)N) stable isotope data. 3. Fish and aquatic invertebrate tissue delta(13)C values increased significantly following extraction for almost all species and tissue types relative to nonextracted samples. In contrast, delta(15)N was affected for muscle and whole body samples from only a few freshwater and marine species and had a limited effect for the entire data set. 4. Lipid normalization models, using C : N as a proxy for lipid content, predicted lipid-corrected delta(13)C for paired data sets more closely with parameters specific to the tissue type and species to which they were applied. 5. We present species- and tissue-specific models based on bulk C : N as a reliable alternative to chemical extraction corrections. By analysing a subset of samples before and after lipid extraction, models can be applied to the species and tissues of interest that will improve estimates of dietary sources using stable isotopes.

A comparison of carbon and nitrogen stable isotope ratios of fish tissues following lipid extractions with non-polar and traditional chloroform/methanol solvent systems.

Stable isotope ratios act as chemical tracers of animal diet, and are used to study food web dynamics. Because carbon stable isotope values are influenced by tissue lipid content, a number of extraction methods have been used to remove lipid bias, but, in some species and tissues, extractions also alter nitrogen isotope values. We have analyzed delta(13)C and delta(15)N in Atlantic bluefin tuna liver and white muscle, and whole Atlantic herring, fish tissues covering a wide range of lipid content (bulk C:N 3.1-12.5). In order to compare delta(13)C and delta(15)N values from traditional chloroform/methanol extractions with non-polar solvent alternatives, we analyzed samples following (1) no treatment, (2) lipid removal using chloroform/methanol (2:1), and (3) Soxhlet extractions using chloroform, diethyl ether or hexane. Chloroform/methanol and chloroform extractions produced the lowest C:N values and highest delta(13)C values. In bluefin tuna, chloroform and hexane extractions significantly altered liver delta(15)N, and all methods significantly altered delta(15)N values in white muscle. Whole Atlantic herring delta(15)N was not altered by any extraction method, while the 2:1 chloroform/methanol extraction most completely removed fish tissue lipid components. Our results indicate that delta(15)N effects are not limited to common chloroform/methanol extractions and suggest that chloroform/methanol is the most effective extraction for delta(13)C correction. Given evidence for delta(15)N alteration among all tested methods, mathematical correction approaches should be further explored as an alternative to lipid correction.