A comparison of habitat use and habitat-specific feeding efficiency by Eurasian ruffe (Gymnocephalus cernuus) and yellow perch (Perca flavescens)

Abstract –  Eurasian ruffe are invading habitats in the North American Great Lakes watershed occupied by commercially important native yellow perch. We conducted laboratory experiments to evaluate potential overlap in habitat (macrophytes, mud, cobble) and food (benthic invertebrates) use. Ruffe and yellow perch both preferred macrophytes > cobble > mud in the light, but only ruffe increased their use of mud in the dark. Neither fish density nor food availability affected habitat preferences, and competition for habitat was not evident. For both species, feeding rates were marginally lower in macrophytes but did not differ between species. Our experiments suggest that if ruffe and yellow perch share a habitat (e.g., during invasion or because of predation risk), competition for space will be weak or absent. However, within a shared habitat, competition for food may occur when food is limiting because neither species has a clear advantage in its ability to consume invertebrates in any habitat.     

Generalist versus specialist: the performances of perch and ruffe in a lake of low productivity

Abstract –  To elucidate the performances of perch and ruffe in oligotrophic lakes, we carried out a field study in reoligotrophic Upper Lake Constance. Both these percids used the same habitat, albeit with different activity patterns. Interspecific competition for food was relevant only in summer when both species fed on zoobenthos. Even then, niche overlap was low, while intraspecific diet overlap was moderate to high throughout the season. Perch did not perform fixed, ontogenetic diet shifts, but used a wide range of prey. During spring and early summer, all size classes were planktivorous, then switched to benthivory and cannibalism in summer, and part of the population reverted to planktivory in autumn. Ruffe, by contrast, fed mainly on chironomid larvae and pupae throughout the year. It is suggested that in lakes of low productivity the euryphagous characteristics of perch, including cannibalism, provide a clear advantage over the benthivorous specialist ruffe in two ways: (i) it allows perch to switch to alternative prey types if one prey type becomes scarce; and (ii) reduces both intra- and interspecific competition for food.     

Yields of European perch from Upper Lake Constance from 1910 to present

Abstract  Commercial yields of perch, Perca fluviatilis (L.), from Upper Lake Constance changed markedly during the 20th century. The perch boom in the 1950s and 1960s is attributed to higher fishing intensity and lake eutrophication. Decreasing yields in recent decades are mainly because of slower growth of perch, while a gradual decrease in year-class strength, and an overall reduction of fishing intensity, might also have contributed to yield reduction. Slower growth is mainly attributed to lake re-oligotrophication and infestation of perch with the pike tapeworm Triaenophorus nodulosus (Pallas). Competition for food with non-native ruffe, Gymnocephalus cernua (L.) is likely of minor importance, while the invasion of the lake by alien macrozoobenthos species has the potential to reduce the food supply for benthivorous perch. Perch yields are assumed to remain at the low level attained at the beginning of the 21st century; however, under changing climate conditions, fluctuations around the long-term mean will probably be wider than in the past.     

Ontogenetic diet profiles and size-dependent diet partitioning of ruffe Gymnocephalus cernuus, perch Perca fluviatilis and pumpkinseed Lepomis gibbosus in Lake Balaton

Abstract –  Life-long diet ontogeny and size-dependent intra- and interspecific diet partitioning of the native ruffe and perch and the introduced pumpkinseed, were studied in Lake Balaton. Estimated intraspecific diet overlap was high in ruffe, whereas in perch and pumpkinseed only the neighbouring size groups exhibited a high diet similarity. Interspecific diet overlap among size groups of the three species was moderate and ≥60% diet overlap occurred only in 13 size group pair variations out of the 429 analysed. The earliest developmental stages of the three species were planktivorous, whereas larger ruffe and some size groups of perch and pumpkinseed fed dominantly on chironomids. Adult perch and pumpkinseed consumed different littoral macroinvertebrates, while the largest perch were piscivorous. Although productivities of the two studied areas differ significantly, this had only little effect on the diet ontogeny and diet partitioning of the three species. Present results suggest that in Lake Balaton these three species effectively partition food resources throughout their life span.     

Habitat and food resource use of perch and roach in a deep mesotrophic reservoir: enough space to avoid competition?

Abstract –  The aim of this study was to test assumptions about the interaction of perch ( Perca fluviatilis L.) and roach ( Rutilus rutilus L.) concerning their food and habitat use in a deep and mesotrophic reservoir. From 1998 to 2001 the fish were caught with gillnets to perform diet analyses. Additionally, vertical gillnets were set to study vertical spatial distribution of both species. The results indicate that in a large and deep reservoir perch and roach are able to avoid competition by separating their niches first in the spatial dimension and then in the dimension of food utilisation. These separations result in low inter- and intraspecific competition of both species. We conclude that these niche separations can widen the juvenile competitive bottleneck to such an extent that the perch are not forced to compete with their older conspecifics during their first year of life, enabling perch to become large and consequently piscivorous.     

Size-dependent predator–prey relationships between pikeperch and their prey fish

Abstract –  Predator–prey interactions in aquatic food webs depend on the sizes of both predator and prey. In the present study, size-dependent interactions between >70 mm total length pikeperch Sander lucioperca (L.) and four different prey species in the biomanipulated Bautzen Reservoir were investigated. Gape widths of 597 pikeperch were measured, and the stomach contents of 806 specimens were analysed. Additionally, total lengths (TL) and body depths of 1448 prey fish were determined. The highest prey length to predator length ratio (PPR) was 0.63. Total lengths of piscivorous pikeperch and total lengths of prey fish [pikeperch, ruffe Gymnocephalus cernuus (L.) and roach Rutilus rutilus (L.)] were positively and linearly related. This was not the case for prey perch ( Perca fluviatilis L.) as all size groups of pikeperch fed strongly on age-0 perch. This study coupled with results of previous studies suggests that predation by pikeperch can have a major impact on the population dynamics of especially perch.     

Habitat use and activity patterns of roach (Rutilus rutilus (L.)), rudd (Scardinius erythrophthalmus (L.)), perch (Perca fluviatilis L.) and pike (Esox lucius L.) in the laboratory: the role of predation threat and structural complexity

Abstract– The role of predation risk and structural complexity in determining the habitat use and activity patterns of roach, rudd and perch was assessed using a series of video-recorded laboratory trials. The time spent in open and structured habitats, vertical swimming heights and activity levels of each species were observed in the presence and absence of a potential, pike, predator. Habitat complexity varied between treatments with artificial stem densities of 200, 400 and 600 stems'm⁻². Predator free trials showed that roach and rudd spent significantly less time in structured habitats than perch. Increasing stem density had no significant effect on the habitat choice of perch but did affect the distribution of roach and rudd. Stem density influenced the vertical swimming height of rudd or perch but not roach, although the effects of habitat complexity on swimming activity were more complicated. Pike were themselves influenced by increases in stem density, only selecting structured habitats when stem densities were less than 600 stems'm⁻². In the presence of a predator, both roach and rudd increased the amount of time spent in structured areas. These observed differences were independent of stem density. Perch, however, decreased the amount of time spent in structural habitats at all stem densities. Predation risk also prompted significant changes in both vertical swimming height and activity levels of potential prey fish. A pike predation success hierarchy of rudd-roach-perch was also observed during the study. The reasons for this pattern are discussed.     

Powan, Coregonus lavaretus (L.), ova predation by newly introduced ruffe, Gymnocephalus cernuus (L.), in Loch Lomond, Scotland

Abstract. Loch Lomond, one of the few British strongholds of the powan, Coregonus lavaretus (L.), has recently been colonized by the ruffe, Gymnocephalus cernuus (L.). The ruffe are now widespread, abundant and one of the commonest fish in Loch Lomond. Analysis of the gut contents of these fish caught on powan spawning grounds in Loch Lomond showed that they, as well as native brown trout, Salmo trutta L., and powan themselves, prey upon powan ova. Ruffe maintained a high winter feeding rate compared with powan and trout and fed on a broad range of benthic prey, of which powan ova formed the greatest biomass (84% of total diet) and dominated the diet numerically (57% of prey items). The observed incidence of powan ova consumption by ruffe was significantly greater than that of both brown trout and powan (P <0·001).     

Prey selection and growth in 0+ Eurasian perch Perca fluviatilis L. in littoral zones of seven temperate lakes

We studied the relationships between the planktonic food base and feeding patterns of juvenile mid-summer/early autumn Eurasian perch Perca fluviatilis L., a common predatory freshwater fish in large parts of Europe and Asia. The feeding of 0+ perch was studied during summer and autumn in littoral habitats of seven lakes with different environmental conditions – four Latvian (Auciema, Riebinu, Vārzgūnes, Laukezers) and three Estonian (Kaiavere, Prossa and Akste) lakes. Simultaneously, the abundance, biomass and structure of zooplankton communities were examined. We focused on the littoral areas because many studies in lakes suggest that littoral habitats are particularly important for 0+ fish growth and survival. We were interested in the question: can the diet and growth of 0+ perch be explained by zooplankton community structure? We also presumed that if the amount of zooplankton is low, more benthic invertebrates will be consumed by 0+ perch. Opposite to expectations, we found that zooplankton always counted for over 90% of diet biomass in perch. There were also clear correlations between the zooplankton biomass in a given lake, the zooplankton biomass in 0+ perch stomachs, and the fish growth rate. The study also suggested that nutrient enrichment can positively impact the 0+ perch feeding conditions in lakes.     

The effects of perch, Perca fluviatilis L., and bronze bream, Abramis brama (L.), on insect emergence and benthic invertebrate abundance in experimental ponds

Abstract The effects of perch, Perca fluviatilis L., and bronze bream, Abramis brama (L.), predation on the production of insects emerging at the water surface and the autumn biomass of benthic macro-invertebrates were assessed in a series of experimental ponds. The study attempted to discover whether fish affect food availability for diving and dabbling ducks in freshwater habitats. Ten ponds (bisected by fine netting) were used for the study: one was left totally fish-free, whilst one half of each of three groups of three ponds was stocked with either perch, bream or perch plus bream. The relative abundance of emerging insects (mainly Chironomidae) was significantly reduced in two perch ponds, two perch + bream ponds and two bream ponds. The autumn standing crops of benthic macroinvertebrates were significantly reduced in one perch pond, three bream ponds and one perch plus bream pond. These results support findings of a contemporaneous large bio-manipulation experiment carried out in two adjacent lakes. During the biomanipulation studies, aquatic invertebrate standing stocks greatly increased after the removal of fish and decreased following restocking.