The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Supplementary data related to this article can be found at: http://
dx.doi.org/10.1016/j.ecss.2014.03.017

/pdf/influence-of-the-invasive-asian-clam-corbicula-fluminea-5wme4s9tmq.pdf

Influence of the invasive Asian clam Corbicula fluminea (Bivalvia: Corbiculidae) on estuarine epibenthic assemblages

Japanese eels (Anguilla japonica) perform large-scale oceanic migrations between their spawning ground and growth habitats in continental waters during life history. However, between these migrations, they spend most of time in growth habitats such as rivers. To investigate the diel and seasonal activities, homing behaviour and home range of yellow-phase Japanese eels in the lower reach of the Tone River, we tracked them throughout a year using a fine-scale positioning system (VPS) based on acoustic telemetry. The tracked eels were generally nocturnal, but not exclusively. They were mainly mobile from spring to autumn, with little or no activity observed during winter. A transport-release experiment showed that most eels returned to their original capture area within 13 days after release. The eels had very small home ranges (mean ± SD = 0.085 ± 0.068 km2), core areas (0.014 ± 0.014 km2) and linear home ranges (744 ± 268 m). They also tended to be distributed on one particular side of the river (right or left bank) and in one particular shore type (revetment or vegetation), rarely moving from one to the other. This study provides evidence for nocturnal, dormancy, homing behaviours, limited habitat use and small home range size in Japanese eels. The eels clearly showed strong fidelity to a “familiar” site, which contrasts with the long distances travelled during upstream and downstream migration phases in the river, and during spawning migrations in the ocean.

Site fidelity, diel and seasonal activities of yellow‐phase Japanese eels (Anguilla japonica) in a freshwater habitat as inferred from acoustic telemetry

Does natural acidity mediate interactions between introduced brown trout, native fish, crayfish and other invertebrates in West Coast New Zealand streams?

https://purews.inbo.be/ws/files/15669455/wgeel_2018.pdf

Report of the Joint EIFAAC/ICES/GFCM Working Group on Eels (WGEEL) 2018

The feeding habits of the European eel Anguilla anguilla (>300 mm total length, L(T)) were compared in two lakes of different environmental state: Lake Grosser Vatersee (LGV), Germany (clear water, mesotrophic and submerged macrophytes), and Lake Vallum (LV), Denmark (turbid, eutrophic and no submerged macrophytes). The density of macrozoobenthos was higher in LV (3500 individuals m(-2)) than in LGV (1500 individuals m(-2)). The abundance of small prey fishes (40-99 mm L(T)) was highest in LV. In LV, A. anguilla fed on macrozoobenthos, in particular, chironomid larvae. In LGV, A. anguilla used fishes as the main food component. Stable isotope analyses confirmed the stomach contents dietary results. The estimated mean +/-s.d. trophic positions of A. anguilla in LGV (3.7 +/- 0.2) was one level higher than those of fish in LV (2.7 +/- 0.2). Based on these results, it is concluded that piscivory among A. anguilla was generally controlled by the density of macrozoobenthos. Stable isotope analysis further indicated that A. anguilla may act as integrators between benthic and pelagic food webs when density of insect larvae is low.

Piscivory and trophic position of Anguilla anguilla in two lakes: importance of macrozoobenthos density.

The role of the eel Anguilla anguilla as a piscivorous species was investigated in a biomanipulation experiment in the mesotrophic Saidenbach Reservoir. The distribution and abundance of the eels were investigated by point abundance sampling, snorkelling and scuba diving. Also, the total yearly consumption of the eel population was compared with the standing stock of prey fishes and the production of roach Rutilus rutilus eggs. A restricted availability of shelter habitats at low water levels had no influence on the distribution of the eels during the nocturnal activity period. Fishes were consumed in low numbers but in high proportions of biomass by large eels. The maximum estimate of the annual consumption of the prey fish standing stock by the eels was 19%. Fish eggs were consumed during a small time period by a large proportion of the eels but the total consumption was <10% of the total annual production of roach eggs. By consuming small individuals of planktivorous fishes, the eels contribute to the biomanipulation programme in the Saidenbach Reservoir.

Consumption, abundance and habitat use of Anguilla anguilla in a mesotrophic reservoir

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Piscivory and trophic position of Anguilla anguilla in two lakes: importance of macrozoobenthos density.

Consumption, abundance and habitat use of Anguilla anguilla in a mesotrophic reservoir