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As concerns about anthropogenic and natural disturbance grow, understanding animal resource use patterns has been increasingly prioritized to predict how changes in environmental conditions, food web structure, and population dynamics will affect biological resilience. Among the tools used to assess resource use, stable isotope analysis has proliferated in ecological studies, particularly in relation to describing intra- and interspecific variation in trophic interactions. Despite a growing need to disseminate scientific information, the inherent limitations of stable isotope ratios and inappropriate synonymizing of distinct evolutionary and ecological processes may mislead ecological inferences in natural systems. This situation necessitates a re-evaluation of the utility of stable isotope ratios to address certain ecological questions. Here, we assess the efficacy of stable isotope ratios to describe two fundamental ecological processes, niche partitioning and individual specialization. Investigation of these processes has increased substantially in accordance with increased access to stable isotope data. This article discusses the circumstances and approaches that are necessary to evaluate niche partitioning and individual specialization, and outlines key considerations for the associated application of stable isotope ratios.

The notion that closely related species resemble each other in ecological niche space (i.e., phylogenetic dependence) has been a long-standing, contentious paradigm in evolutionary biology, the incidence of which is important for predicting the ecosystem-level effects of species loss. Despite being examined across a multitude of terrestrial taxa, many aspects of niche conservatism have yet to be explored in marine species, especially for characteristics related to resource use and trophic behavior (Eltonian niche characteristics, ENCs). We combined ENCs derived from stable isotope ratios at assemblage- and species-levels with phylogenetic comparative methods, to test the hypotheses that benthic marine fishes (1) exhibit similar assemblage-wide ENCs regardless of geographic location and (2) display phylogenetically dependent ENCs at the species level. We used a 12-species sub-set of the monophyletic group Rajidae sampled from three independent assemblages (Central California, Gulf of Alaska, and Northwest Atlantic), which span two ocean basins. Assemblage-level ENCs implied low trophic diversity and high evenness, suggesting that Rajidae assemblages may exhibit a well-defined trophic role, a trend consistent regardless of geographic location. At the species level, we found evidence for phylogenetic dependence of ENCs relating to trophic diversity (i.e., isotopic niche width; SEAc). Whether individuals can be considered functional equivalents across assemblages is hard to ascertain because we did not detect a significant phylogenetic signal for ENCs relating to trophic function (e.g., trophic position). Thus, additional, complimentary approaches are required to further examine the phylogenetic dependence of species functionality. Our approach illustrates the potential of stable isotope-derived niche characteristics to provide insight on macroecological processes occurring across evolutionary time, which could help predict how assemblages may respond to the effects of species loss.

Stable isotope data have made pivotal contributions to nearly every discipline of the physical and natural sciences. As the generation and application of stable isotope data continues to grow exponentially, so does the need for a unifying data repository to improve accessibility and promote collaborative engagement. This paper provides an overview of the design, development, and implementation of IsoBank (www.isobank.org), a community-driven initiative to create an open-access repository for stable isotope data implemented online in 2021. A central goal of IsoBank is to provide a web-accessible database supporting interdisciplinary stable isotope research and educational opportunities. To achieve this goal, we convened a multi-disciplinary group of over 40 analytical experts, stable isotope researchers, database managers, and web developers to collaboratively design the database. This paper outlines the main features of IsoBank and provides a focused description of the core metadata structure. We present plans for future database and tool development and engagement across the scientific community. These efforts will help facilitate interdisciplinary collaboration among the many users of stable isotopic data while also offering useful data resources and standardization of metadata reporting across eco-geoinformatics landscapes. [ABSTRACT FROM AUTHOR]

Misty Groupers (Hyporthodus mystacinus) are one of the largest and most geographically widespread grouper species and one of the few grouper species known to occur at depths greater than 200 m. However, aspects of their basic biology, behavior, and ecology remain poorly understood, leaving significant gaps in our ability to evaluate their functional role throughout the vertical water column, as well as our understanding of their conservation needs in a changing ocean. Through in-situ video observation obtained using deep-sea landers in both The Bahamas and Cayman Islands over multiple years, we documented Misty Grouper occurrence up to 470 m depth in the mesopelagic zone. These observations provide a new depth range extension for the species and illuminate the potential importance of deep-water habitats for large grouper species in the wider Caribbean. [ABSTRACT FROM AUTHOR]

This article explores the use of stable isotopes in studying fish biology. It focuses on four main themes: understanding isotopic discrimination patterns, determining energy distribution in fish communities, assessing the impact of human activity on fish foraging and fitness, and exploring nontraditional stable isotope systems. The article presents various studies that investigate these themes, including the influence of maternal provisioning on young fish tissues, the use of non-lethal tissues for analysis, and the effects of environmental factors on fish communities. It also discusses the implications of human disturbance on fish diet, habitat use, and overall fitness. The article emphasizes the importance of stable isotopes in understanding fish ecology and physiology in a changing world. Additionally, the document discusses the advancements in analytical technology that have made non-traditional isotope systems more accessible to fish biologists, such as Calcium and Zinc. It also highlights the potential of stable isotope analysis in uncovering the functional roles of ancient fish lineages. The document concludes by stating that the continued development of isotopic tools will contribute to the management and conservation of global fish populations. [Extracted from the article]

Effective management and conservation of threatened species biodiversity requires knowledge of reproductive biology, such as cyclicity, mode, and age at maturity. We combined reproductive endocrinology and in-situ ultrasonography to examine reproductive characteristics of female Caribbean reef sharks Carcharhinus perezi, a widely distributed, threatened marine predator which remains largely understudied throughout its range. Unique to this study was the opportunity to conduct longitudinal assessments of two individuals, recaptured across multiple seasons during sampling in The Bahamas. Within- individual, paired hormone analyses and in-situ ultrasounds of female sharks that were confirmed as either pregnant, non-pregnant, or reproductively active, suggest a biennial reproductive cycle for Carcharhinus perezi. This unique opportunity to assess the reproductive biology of the same individuals over time underscore the importance of repeated sampling for elucidating population reproductive cyclicity of highly mobile sharks in the wild. [ABSTRACT FROM AUTHOR]

Fisheries-independent data on the diversity, relative abundance, and demographic structure of poorly studied, threatened oceanic sharks are absent from much of the western North Atlantic Ocean, where multiple oceanic shark species have experienced significant population declines. Resource-limited management approaches require the identification of critical habitats or aggregation sites worthy of protection and enforcement. Data were collected on oceanic sharks using pelagic longline surveys, targeted baiting, and opportunistic encounters in oligotrophic open-ocean habitats of north-eastern Exuma Sound (NES), The Bahamas. The oceanic epipelagic shark community was also characterized using targeted baiting off Columbus Point, Cat Island (CI), a seamount north of San Salvador (SSSM), and the northwestern tip of Mayaguana. Pelagic longline surveys suggested that the relative abundance of sharks at NES was low (shark catch-per-unit-effort: 0.0007 sharks hook−1 h−1; 2.3 sharks per 1000 hooks). Silky sharks Carcharhinus falciformis, particularly juveniles (134 ± 39 cm stretched total length; mean ± SD STL), were the most common. Targeted baiting suggested oceanic whitetip sharks C. longimanus were abundant at CI, where large adults (245 ± 23 cm STL), most of which were females (83.8%, n = 98 of 117) that were gravid (65.7%; n = 46 of 70 assessed for pregnancy), dominated the aggregation. Many (20.5–26.5%, n = 24–31 of 117 depending on assumptions regarding tag loss) were recaptured or resighted at CI for up to five years. Silky sharks dominated catches at SSSM. Oceanic sharks, particularly adults, were sometimes caught or observed alongside short-finned pilot whales Globicephala macrorhynchus or tunas. Although The Bahamas offers threatened oceanic sharks refuge from fishing across its entire jurisdiction, these data suggest that some fixed features, including sites such as CI and potentially SSSM, are important aggregation sites with high regional conservation value and should be prioritized by fisheries managers and enforcement officials. [ABSTRACT FROM AUTHOR]

Robustly quantifying dietary resource use and trophic position using stable isotopes requires accurate trophic discrimination factors (TDF; Δ13C and Δ15N for carbon and nitrogen, respectively), defined as the isotopic difference between consumer and diet. Early TDF studies converged on values of around 1.0‰ for Δ13C and 3.4‰ for Δ15N but more recent work indicates that TDF values may be more nuanced, depending on taxa, tissues, trophic level and diets. Yet, the relative importance of these factors remains unclear.Focusing on vertebrates (birds, fish, herptiles and mammals), we conducted a literature review of 279 studies that estimated TDF values and used a Bayesian framework to determine how tissue type, trophic level and diet source influence variation in Δ13C and Δ15N. Additionally, we reviewed 358 trophic ecology studies to determine if studies accounted for these factors during their TDF selection process.For Δ13C, vertebrates showed consistent patterns among tissue types (likely influenced by amino acid composition) and between trophic levels and diet sources (likely a result of dietary protein content and metabolic routing). Comparatively, for Δ15N, vertebrates showed considerable variation among tissue types and trophic levels, likely due to differences in tissue synthesis and physiological capabilities. Overall, Δ13C ranged from −5.1‰ to 9.1‰ and Δ15N from −3.3‰ to 9.7‰, underscoring that 1.0‰ for Δ13C and 3.4‰ for Δ15N are not universally appropriate. Moreover, both Δ13C and Δ15N varied by more than 9‰ within a single species and tissue type, demonstrating that using TDF values from the same, or similar, species may not be appropriate if diet and trophic level are not considered.Despite the importance of diet source on TDF values, most trophic ecology studies did not account for it. Further, most fish studies relied on literature review values that failed to account for tissue type, trophic level and diet source. To aid ecologists in diet and trophic assessments of vertebrates, we used our meta‐analysis to model taxon‐specific TDF estimates (mean ± SD) for each tissue type, trophic level and diet source combination. These more refined TDF values should improve ecological assessments that use stable isotopes. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]