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Piscivorous birds in aquatic ecosystems exert predation pressure on fish populations. But the site‐specific impact on fish populations, including stocked and commercially used fish species, remains disputed. One of the key questions for the management of piscivorous birds and fish is determining the origin of prey and thus which fish populations are targeted by the birds. We addressed this question by provenancing otoliths (earstones) of fish obtained from regurgitated pellets of piscivorous birds by otolith microchemistry analysis. We retrieved otoliths from regurgitated pellets of great cormorants (Phalacrocorax carbo sinensis) collected every 2 weeks for 2 years from breeding and roosting colonies at Chiemsee in Bavaria, Germany, and classified them according to family or species. We collected water samples from Chiemsee and potential surrounding foraging grounds. We measured the strontium (Sr) 87Sr/86Sr isotope ratio and Sr mass fraction of water and otoliths using (laser ablation) inductively coupled plasma‐mass spectrometry. We assigned otoliths from regurgitated pellets to habitat clusters of origin by comparing the Sr isotopic and elemental composition of otoliths and waterbodies. In 36% of cormorant pellets collected at Chiemsee, prey was assigned to waterbodies distinct from Chiemsee. Furthermore, cormorants used different foraging sites during 1 day. Microchemical provenancing of prey remains can contribute to identifying foraging sites of piscivorous birds and to what extend the birds switched among foraging sites. [ABSTRACT FROM AUTHOR]

• Landscape had a lower effect on aphids and their parasitoids than fertilisation. • Fertilisation affected plants positively. • Fertilisation affected aphids and primary parasitism rate negatively. • Fertilisation had no effect on secondary parasitism rate. • H 2 ' and generality between parasitoids are affected by landscape and fertilisation. Agricultural intensification can impact agrobiodiversity in several ways such as in terms of population densities, community composition and food web interactions across all trophic levels. This effect can be investigated at two scales: field-scale and landscape scale. Here it was assessed how the impact of fertilisation (within field) and landscape complexity (within landscape) impact cereal aphid-primary parasitoid-secondary parasitoid systems in winter wheat in Germany. A newly developed molecular technique was used to quantify species-specific linkages between aphids, primary parasitoids and secondary parasitoids sampled in fertilised and unfertilised plots in either simple or complex structured landscapes. The results show a stronger effect of fertilisation than landscape complexity on the groups: fertilisation positively affected the crop plants while it negatively affected both the density of the cereal aphid Sitobion avenae and its primary parasitism rates whereas no effect on the level of secondary parasitism rates was observed. Landscape complexity had no effect on plants, aphids, as well as on primary parasitism rate. In case of secondary parasitism rate there was an effect in interaction with sampling date. Field identity accounted for the strongest effect on parasitoid community composition (10.6% of the variance) from all tested variables, while fertilisation and landscape complexity had almost no effect (1.1% and no effect). Nevertheless, a weak cascading effect of both environmental factors could be observed as the primary-secondary parasitoid network structure responded to both. However, these observed effects on food webs strongly depended on species identity, highlighting the need of species-level food web assessment. [ABSTRACT FROM AUTHOR]

The focus of this study was to assess the potential of otolith microchemistry as a fishery management tool for different European freshwater fish species in an Alpine foreland with a diverse range of different water bodies but low geological variation. 87Sr/86Sr isotope ratios and Sr/Ca ratios in water samples from 26 habitat sites in a pre-alpine catchment region around lake Chiemsee, Germany, an important region for recreational and economic fisheries, were analysed. 87Sr/86Sr isotope ratios and the Sr/Ca ratios in otoliths of 246 fish out of 16 species were determined using (laser ablation) inductively coupled plasma mass spectrometry ((LA)-ICP-MS). Habitats could be differentiated into seven clusters when using the 87Sr/86Sr isotope and Sr/Ca ratios in water in combination. When using the 87Sr/86Sr isotope ratio as individual parameter, the strontium isotope groups (SIGs) based on the 87Sr/86Sr isotope ratios including the measurement uncertainties justified a three-cluster solution. The direct comparison of 87Sr/86Sr isotope ratios in water and otolith samples allowed to identify fish that a) might have migrated, b) were transferred from other water bodies or c) stocked from fish farms. Sr/Ca ratios in water and otoliths were highly correlated, although significant differences between species from the same environment were documented. Sr/Ca ratios in sagittae of Perca fluviatilis were about 64–60% of those in sagittae of Coregonus spp and of lapilli of roach Rutilus rutilus from the same habitats, respectively. Partition coefficients for water to otolith Sr/Ca ratios were calculated and differed between species. Discrimination of fish otoliths according to habitat clusters by combining 87Sr/86Sr and Sr/Ca ratios was possible with success rates of up to 100% for whitefish Coregonus spp., 90% for European perch Perca fluviatilis, 87% for cyprinids, and 89% European grayling Thymallus thymallus, and 68% for salmonids. When using the 87Sr/86Sr isotope ratios as single parameter, assignment results were generally worse, except for salmonids, where an improved accuracy of 79% could be achieved, or for cyprinids when the number of clusters was reduced from five to three. The study indicates that otolith microchemistry has great potential to serve as a fishery management tool at smaller spatial scales such as in the studied Alpine foreland when combining the 87Sr/86Sr and Sr/Ca ratios, and considering the type and spatial distribution of habitats, the species and question under investigation. • Otolith microchemistry applied in an area with limited geological variability. • Fish transferred, stocked or migrated were identified. • Sr/Ca ratios in water predict Sr/Ca ratios in otoliths. • Fish species-specific Sr discrimination from water into otoliths. • European freshwater fish species assigned to habitat clusters of origin. [ABSTRACT FROM AUTHOR]