Cascading effects of temperature alterations on trophic ecology of European grayling (Thymallus thymallus)

Abstract

The aims of this project were to study: diet composition, food selectivity and the phenology of different prey items in grayling’s (Thymallus thymallus) diet. It was hypothesized, that alterations in mayfly emergence, caused by reservoir-induced thermal changes, have consequences for trophic ecology of drift-feeding fish. Sampling of fish and macroinvertebrates were conducted in two closely located rivers, one human-modified and the other an undisturbed river. Grayling preyed mainly on aquatic insects, but only mayflies were preferred. Seasonal changes of the fish diet were observed, and air temperature is considered a predictor of prey occurrence with different time lags, depending on the biology of the organisms. Significant differences in the abundances and probability of mayfly occurrence between two studied rivers were shown. The observed phenological shift suggests that distorted environmental cues were experienced by the Ephemeroptera in the modified river. The “lost generation” of insects which failed to complete development became a new food for fish. The results presented indicate that reservoir-induced thermal alterations in the rivers, similarly to climate change, can lead to a chain of consequences in the ecosystems. Taking into consideration the projected climate scenarios, further monitoring and forecasting of these effects are considered an important step for future mitigating actions and adaptive management of water resources.

Higher growth variability and stronger responses to temperature changes in wild than hatchery‐reared sea trout (Salmo truttaL.)

“…Although the main aim of the analysis was to test the hypothesized effects of seawater temperatures on fish growth at sea, we also tested the potential thermal influences on fish growth in freshwater. It was assumed that in the studied river system, the surface and water temperatures are closely related (Smoliński & Glazaczow, 2019;Webb & Nobilis, 1997). Thus, the average annual surface temperature aggregated over the study area (54-55 °N-16-19 °E) was included in the analysis as a proxy of the water temperature experienced by the fish in freshwater.…”

Body mass and latitude predict the presence of multiple stressors in global vertebrate populations

“…Global vertebrate populations are in decline (WWF 2018;He et al 2019), a fact attributed to the overarching trend of anthropogenic stressors (or 'threats') increasing in line with human populations (Johnson et al 2017). Such threats can act at both a local and global scale, with locally detrimental stressors such as the overharvesting of species for food (Zhou & Smith 2017) occurring simultaneously against a backdrop of global stressors such as climatic change which can alter energy flows (Bartley et al 2019), impact trophic interactions (Smoliński & Glazaczow 2019), and increase the physiological stress of populations (Iknayan & Beissinger 2018). Thus, as human populations increase, biodiversity is being exposed not only to increasing levels of stress, but to multiple stressors impacting simultaneously; with resulting effects creating novel challenges for the effective conservation of species (Côté et al 2016).…”