1,720,970 research outputs found
Varying organic content in fish otoliths: Effects on SIMS-based δ18O measurements and possible corrections
No full textVarying organic contents in otoliths have complex and sometimes counterintuitive effects on intra-otolith δ18O measurements. This is often addressed by roasting otoliths or applying fixed corrections, however, the underlying chemical and physiological mechanisms involved are poorly understood and have not been tested in a quantitative manner, potentially rendering such corrections unreliable. Using high-resolution secondary ion mass spectrometry (SIMS) measurements of δ18O values paired with OH/16O ion ratios as organic proxy, we derived quantitative relationships of these measurements over the entire life of a large sample of northern pike (Esox lucius) otoliths from freshwater and brackish habitats. We assessed OH/16O ion count ratio as an organic tracer, and estimated its relationship with δ18O determinations. We developed a pointwise correction approach that accounted for variations in otolith organic contents. OH/16O ion ratio profiles agreed with other organic proxies, confirming them as reliable tracer of organic content. We detected an inverse relationship between δ18O values and OH/16O ion ratio, with elevated OH/16O ion ratios near otolith cores. OH/16O ratios decreased with distance to the core. Pairwise corrections for the effect of OH/16O ratios on δ18O values resulted in a mean offset between uncorrected and corrected values of 0.52 ‰, suggesting an approximately 2°C bias towards warmer temperature if uncorrected data were to be used for δ18O thermometry. Simultaneous determination on organic- and inorganic-bound oxygen resulted in a negative offset of δ18O, which varies with the life history of individual fish. Varying offsets in δ18O values within individual life histories could be accounted for using our correction. We recommend future SIMS-based δ18O thermometry studies to estimate the local organic content to assess whether correction is warranted. We further offer more general recommendations on how future studies may assess whether corrections for organics are necessary
Corroborating age with oxygen isotope profiles in otoliths: consequences for estimation of growth, productivity and management reference points in northern pike (<i>Esox lucius</i>) in the southern Baltic Sea
No full textAccurate and precise age estimates are crucial for assessing the life-history of fish and providing management advice for fisheries, but age validation studies remain rare or absent in many species. Aging from scales is common, as it is non-lethal, but potential for underaging old fish exists. Using 85 northern pike (Esox lucius) collected from the southern Baltic Sea in Germany as a model, we corroborated age readings based on annual cycles of oxygen isotopes (δ18O) in otoliths to infer the timing and validity of growth, so as to compare results with visual age estimations from scales and otoliths. Otoliths were accurate and precise, while age readings from scales systematically underestimated the age of old pike. Fitting population-level von Bertalanffy growth models to the size-at-age data estimated via δ18O-profiling, otoliths or scales revealed a larger terminal length (L∞) and a lower body growth coefficient k in scale-aged fish compared to otolith and corroborated age data. Populating an age-structured model with structure-specific growth model parameters demonstrated that the maximum sustainable yield (MSY) was estimated to be about 37% lower using scale-informed growth models relative to growth models fitted to corroborated and otolith-based size-at-age data. Thus, pike populations assessed and modeled based on scale age readings might appear less productive than they really are. Using scale-based ages to inform management regulations may therefore result in too conservative management and lost biomass yield, while instilling unrealistic angler expectations as to the trophy potential of the fishery
Variable habitat use supports fine-scale population differentiation of a freshwater piscivore (northern pike, Esox lucius) along salinity gradients in brackish lagoons
No full textIn mobile animals, selection pressures resulting from spatio-temporally varying ecological factors often drive adaptations in migration behavior and associated physiological phenotypes. These adaptations may manifest in ecologically and genetically distinct ecotypes within populations. We studied a meta-population of northern pike ( Esox lucius ) in brackish environments and examined intrapopulation divergence along environmental gradients. Behavioral phenotypes in habitat use were characterized via otolith microchemistry in 120 individuals sampled from brackish lagoons and adjacent freshwater tributaries. We genotyped 1514 individual pike at 33 highly informative genetic markers. The relationship between behavioral phenotype and genotype was examined in a subset of 101 pikes for which both phenotypic and genomic data were available. Thermosaline differences between juvenile and adult life stages indicated ontogenetic shifts from warm, low-saline early habitats towards colder, higher-saline adult habitats. Four behavioral phenotypes were found: Freshwater residents, anadromous, brackish residents, and cross-habitat individuals, the latter showing intermediary habitat use between brackish and freshwater areas. Underlying the behavioral phenotypes were four genotypes, putative freshwater, putative anadromous, and two putatively brackish genotypes. Through phenotype-genotype matching, three ecotypes were identified: (i) a brackish resident ecotype, (ii) a freshwater ecotype expressing freshwater residency or anadromy, and (iii) a previously undescribed intermediary cross-habitat ecotype adapted to intermediate salinities, showing limited reliance on freshwater. Life-time growth of all ecotypes was similar, suggesting comparable fitness. By combining genetic data with lifelong habitat use and growth as a fitness surrogate, our study revealed strong differentiation in response to abiotic environmental gradients, primarily salinity, indicating ecotype diversity in coastal northern pike is higher than previously believed
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No full textAccurate 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 (δ
18O) 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 ((Formula presented.)) was larger, and the growth coefficient (Formula presented.) was lower for scale ages than for corroborated age and otolith age estimates. Consequentially, scale-informed population models overestimated maximum sustainable yield ((Formula presented.)), biomass at (Formula presented.) ((Formula presented.)), relative frequency of trophy fish ((Formula presented.)), and optimal minimum length limit but underestimated fishing mortality at (Formula presented.) ((Formula presented.)). 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.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Water isotope values in samples collected June 2019, March 2020 and July 2020 along estuarine systems at the Baltic Sea coast
No full textStable isotopes (δ2H and δ18O) were analyzed in water samples collected at 68 spots along the Schlei, the Zingster Bodden chain, and the Rügener and Greifswalder Boddens in June 2019, March 2020, and July 2021. Transect samples were taken at shores from 0.3 to 0.6 m below water surface, using a pipette, and directly transferred into measurement vials. Isotope analysis was conducted at IGB Berlin, using a Picarro L2130-i cavity ring-down spectrometer. Water chemical parameters were measured in-situ with a WTW multiparameter device (Multi 3630 IDS), equipped with a WTW TetraCon 925 electrical conductivity measuring cell. The data give information about the spatial isotope variability along the transects
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Water isotope time series (March 2020 - March 2021) of samples collected at A. P. Møller Skolen, Kleine Breite, Schlei
No full textTime series of stable isotopes (δ2H and δ18O) were analyzed in water samples collected near the A. P. Møller Skolen, Schleswig (Kleine Breite, Schlei), in biweekly to monthly intervals between March 2020 and March 2021. Water was sampled with a pipette from ca. 0.5 m below water surface and directly transferred into a measurement vial. Isotope analysis was conducted at IGB Berlin, using a Picarro L2130-i cavity ring-down spectrometer. Water chemical parameters were measured in-situ with a modular WTW 3440 multiparameter devices and regularly calibrated conductivity cells (MPP 930 IDS, TetraCon® 925-P). The data give information about the seasonal isotope amplitude at the sampled locations and about spatial variability along the transects
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