Longitudinal patterns of fish assemblages in European boreal streams

Abstract

Fish assemblages are known to change from headwaters to river outlets. Still, our knowledge of this change is often approximate or sporadic. In this study, we quantified the average longitudinal change from a large electrofishing data set of boreal streams in Northern Europe. The average species richness increased from headwaters to medium-sized rivers but levelled off when reaching large rivers. Existence of some headwater specialist fish species, e.g. brook trout (Salvelinus fontinalis), was interpreted to support the fish zonation concept over the concept of accumulative addition of species downstream. The traditional fish zonation concept developed in Western Europe suggests four zones from headwaters to river outlets, the trout zone, the grayling zone, the barbel zone and the bream zone. Of these, only the trout zone was clearly present with a high dominance in the headwaters of the streams studied. For the North European boreal streams, we suggest a zonation concept with three dominating fish species from headwaters downstream, brown trout (Salmo trutta), bullhead (Cottus gobio) and Atlantic salmon (Salmo salar). Discovered longitudinal shifts in fish guild compositions offered an opportunity for an ecological interpretation of the data and a promising basis for bioassessment.

American mink (Neovison vison) preying on hatchery and wild brown trout (Salmo trutta) juveniles in semi‐natural streams

“…Our study has management implications specifically in small streams, which are important for brown trout (Jonsson et al, 2001;Sutela et al, 2020;Vehanen et al, 2020). Survival during the juvenile stages is highly important for the growth of the brown trout populations (Elliott, 1994), and predation is one of the main drivers of fish community structure (Gebrekiros, 2016).…”

Geodiversity as a potential indicator of stream health in ecological quality assessment systems

“…Concerning our findings about weak relationships between geodiversity and diatom and macroinvertebrate and fish richness, it possibly shows that other environmental descriptors play a more important role than the richness of hydrogeomorphological features in shaping species richness. Indeed, freshwater species richness and endemism patterns are the result of climate, productivity and biogeographical history, so factors such as river connectivity, upstream barriers and isolation are likely to provide a better understanding of the distribution of fish species at the regional scale than local scale factors, such as hydromorphology or pollution (Griffiths et al, 2014; Oikonomou et al, 2014; Sutela et al, 2020). Previous works on freshwater fishes have shown that total species richness was also influenced by drainage characteristics and factors related to area, energy availability (i.e., net primary productivity) and climatic parameters (annual rainfall and average annual temperature) (Boll et al, 2016; Griffiths et al, 2014; Pelayo‐Villamil et al, 2015; Tedesco et al, 2017; Tisseuil et al, 2013).…”

Longitudinal Patterns in Fish Assemblages after Long-Term Ecological Rehabilitation in the Taizi River, Northeastern China

“…For example, zonation concepts are used for description rather than explanation of longitudinal changes. Another shortcoming of zonation concepts is that fish zones may be defined according to the appearance of local indicator species, which limits their widespread application [65][66][67]. For the lacking explanation for the longitudinal fish composition change, two processes, involving species addition and species replacement have been proposed [23,29,31,66].…”

“…To overcome the dependence on the occurrence of indicator species, zonation concepts can be refined by a new classification system (e.g., general biocoenotic terms and the intensity of human activities) [65][66][67]. In the Taizi basin, anthropogenic disturbances were the key drivers in shaping the longitudinal fish organization pattern.…”