Distribution and feeding of juvenile fish on invertebrates in littoral reed (Phragmites) stands

Abstract – Complex interactions between fish predators and their prey have been found in structurally complex habitats built by submerged macrophytes. In contrast, the role of comparably structured littoral reed stands in shaping biotic interactions has not been investigated. We hypothesised that reed stands may be a valuable feeding habitat for juvenile fish, and that perch and roach may segregate along the spatial and dietary niche dimensions between reed and open water habitats. In contrast, the protection effect of reed against predators was assumed to be rather low because of the lower plant volume infested in reed when compared with submerged macrophytes. We analysed biomass and growth of juvenile (age 0 and age 1) perch and roach in littoral reed habitats and in open water habitats in front of the reed in the shallow Lake Müggelsee over 4 months in 2000. Sampling was conducted by point-abundance electrofishing over the full diel cycle (day, dusk, night, dawn). Zooplankton and benthos biomasses were determined in both habitats as well, and habitat-specific diet of fish was assessed during day and night. Roach were more frequent than perch in both habitats. Food of roach included a higher proportion of zooplankton, whereas perch fed more on macroinvertebrates. Overall, diet overlap between the fish groups was high. Diel distribution of fish did not follow the expectations of habitat segregation between perch and roach. Instead, the function of reed as refuge habitat against littoral piscivores (mainly birds) may have caused the strong daytime preference for reed in almost all fish groups, which was partly upset by roach at night. The higher behavioural plasticity of roach may explain their good performance even under the conditions of high structural complexity.     

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.     

Effects of predator-induced visual and olfactory cues on 0+ perch (Perca fluviatilis L.) foraging behaviour

Abstract –  Foraging juvenile fish with relatively high food demands are usually vulnerable to various aquatic and avian predators. To compromise between foraging and antipredator activity, they need exact and reliable information about current predation risk. Among direct predator-induced cues, visual and olfactory signals are considered to be most important. Food intake rates and prey-size selectivity of laboratory-reared, naive young-of-the-year (YOY) perch, Perca fluviatilis , were studied in experiments with Daphnia magna of two size classes: 2.8 and 1.3 mm as prey and northern pike, Esox lucius , as predator. Neither total intake rate nor prey-size selectivity was modified by predator kairomones alone (water from an aquarium with a pike was pumped into the test aquaria) under daylight conditions. Visual presentation of pike reduced total food intake by perch. This effect was significantly more pronounced (synergistic) when visual and olfactory cues were presented simultaneously to foraging perch. Moreover, the combination of cues caused a significant shift in prey-size selection, expressed as a reduced proportion of large prey in the diet. Our observations demonstrate that predator-induced olfactory cues alone are less important modifiers of the feeding behaviour of naive YOY perch than visual cues under daylight conditions. However, pike odour acts as a modulatory stimulus enhancing the effects of visual cues, which trigger an innate response in perch.     

A test of crayfish predatory and nonpredatory fish species as bait in crayfish traps

The effectiveness of different crayfish: predatory (pike, Esox lucius L., perch, Perca fluviatilis L.) and nonpredatory [roach, Rutilus rutilus (L.) , and bream, Abramis brama (L.)] fish species as bait for noble crayfish, Astacus astacus L., was tested. Trapping was conducted in two lakes in Norway and Lithuania. Nonpredatory bream and roach were superior as noble crayfish bait compared with predatory perch and pike. In the Norwegian lake bream was also superior to roach. Pike- and perch-baited traps tended to catch larger crayfish than bream- and roach-baited traps. An alarm or avoidance response to different live or dead fish predators (e.g. pike or perch) might exist and could be more pronounced in smaller crayfish, thus explaining that pike and perch as bait catch fewer and larger crayfish. Another explanation could be that the odour of pike and perch flesh is simply less attractive or diffuses more slowly through the water. Selecting the most efficient bait will increase the catch per unit effort (CPUE); in this study there was a four-fold variation in CPUE between the best and worst bait type. In test-fishing/monitoring surveys it is important to standardize the bait type used.     

Interactions between juvenile roach or perch and their invertebrate prey in littoral reed versus open water enclosures

Abstract – Structural complexity offered by submerged macrophytes was shown to have fundamental effects on interactions between fish and their prey. However, less information is available for littoral reed (Phragmites spp.) stands. A previous field study found juvenile roach and perch to coexist within the reed stands. It was suggested that reed serves mainly as refuge against littoral piscivores, such that coexistence of perch and roach in the reed was externally forced. Several hypotheses were raised to explain why roach nevertheless showed good growth performance. Three of the hypotheses were tested experimentally. In particular, we were interested in how the confinement of fish to one of the reed or open water habitats alters feeding and growth patterns of juvenile age‐1 perch and roach. Fish were stocked separately into littoral enclosures for a 3‐week period in densities which had been found in the surrounding lake. Development of zooplankton and macroinvertebrate biomasses was observed by sampling the enclosures three times over the experimental period. Individual consumption of prey groups by the fish was calculated with a bioenergetics model, and was compared with prey group biomass in the enclosure treatments. The confinement of fish to one littoral habitat had clear effects on diet composition and growth rates. Roach fed less zooplankton and partially switched to macroinvertebrates in the reed enclosures when compared with the open water treatments, and consequently their growth rates were lower in the reed. Perch preferred macroinvertebrates in both habitats, without any difference in growth rates between the habitats. Effects of fish predation on both zooplankton and macroinvertebrate biomass were low in open water and reed enclosures. Daily consumption rates were only in a few cases higher than 40% of the available biomass of the respective prey group, but mainly were below 10% of available biomass. Therefore, we argue that both the diel horizontal migrations of roach and the relatively low consumption rate of fish when compared with the available resource biomass allow the coexistence of juvenile roach and perch in littoral reed stands.     

Predation risk allocation or direct vigilance response in the predator interaction between perch (Perca fluviatilis L.) and pike (Esox lucius L.)?

Abstract –  Predation risk allocation hypothesis predicts that a prey's response to predator depends on prey's previous experience on predator. Here we tested whether the group of three perch respond differentially to pike, predator of perch, depending on the timing of high constant (HC) and high unpredictable (HU) risk periods within low constant risk periods in short-term (10 h) experiments, and whether the response is stronger during a HU risk period than during a HC risk period. Perch clearly erected the dorsal fin in response to predation risk treatments (pike odour only, odour and visible pike). Decrease in activity and increase in shoaling behaviour were observed mainly during high risk periods. However, the perch's responses to pike did not differ statistically between periods of various levels of predation risk or depending on the timing of high risk situations within constant low risk periods, and thus, suggesting that perch respond mainly to changes in the current predation risk.     

Temperature‐ and light‐dependent ratio of energy gain to metabolic costs explains spatial and temporal habitat use of zooplanktivorous fish

Understanding the forces that drive habitat selection of species in communities is important in both ecology and evolution. In nature, species face variation in competition, predation and physical characters among habitats. Vendace (Coregonus albula (L.)) is a specialised zooplanktivorous fish predominantly using deeper water in lakes during summer, while roach (Rutilus rutilus (L.)) uses mainly the shallow littoral zone as well as the upper layer of the pelagic zone. To understand mechanisms behind habitat use of these species, I first conducted a predation experiment to investigate their sensitivity to predation by perch (Perca fluviatilis L.). Second, I performed a foraging experiment using different temperature and light treatments. I then used metabolic calculations to estimate energetic costs when foraging. I found no difference between species regarding sensitivity to predation. Vendace was the most efficient forager on zooplankton but also swam faster spending more energy compared to roach. Roach had a comparatively high metabolic rate in the lowest temperature, where their foraging efficiency was lowest. The energy gain ratio at 6°C was highest for vendace, while it was lowest for roach. In the highest temperature (18°C) and the lowest light level (1 lux), both species were similar in their energy gain ratio. The relative energy gain ratio provides a mechanism to explain habitat distribution for the two species. An increased understanding of the role of metabolism in combination with biotic interactions and habitat use may help to foresee effects of environmental change for different species.     

The effect of lakes on the stream fish fauna

The effect of natural lakes on the fish species distribution in surrounding streams was studied using electrofishing survey data from 3281 localities in streams throughout Sweden. The occurrence of lake fish (northern pike, European perch, roach and burbot) was significantly higher close to lakes, both up- and downstream, as compared to localities further up- or downstream of lakes. Correspondingly, the occurrences of stream fish (brown trout, grayling, European minnow and bullheads) were lower close to lakes. It is suggested that the lower occurrences of the latter close to lakes be due to biotic interaction with lake fish, especially predation from pike and burbot. The results strongly indicate that the effect of lakes on water temperature, drift of plankton and invertebrates or the moderating effect on water fluctuations and quality did not influence the stream fish fauna to the same extent as the presence of lake fish in a zone up- as downstream of the lakes. Lakes function as a reservoir of strong predators and competitors.     

Habitat distribution of fish in late summer: changes along a nutrient gradient in Danish lakes

Abstract – The horizontal distribution of fish in lakes varies with species, age, predation risk, vegetation coverage and water clarity. Although sporadic data are available for specific lakes, little is known about how habitat distribution generally changes along a gradient in nutrients and clarity. Here we analyse littoral and pelagic fish catch data for 34 Danish lakes (covering 94 lake years) with contrasting total phosphorus (TP) concentrations and mean depth levels (but mainly eutrophic and shallow). Electrofishing was conducted during day along the shore or along the edge of the reed belt if such existed. Gill nets were set overnight for 18 h in open water. We calculated a littoral proportion as: LITPRO = (100 × number caught by electrofishing in the near‐shore area)/(number caught by electrofishing in the near‐shore area and nets in the open water). At all summer TP concentrations LITPRO was high for several ‘littoral’ species such as gudgeon (Gobio gobio), rudd (Scardinius erythrophtalmus) and pike (Esox lucius) and low for more typical pelagic species like pikeperch (Sander lucioperca), ruffe (Gymnocephalus cernuus) and smelt (Osmerus eperlanus). However, for many of these species including the dominant roach (Rutilus rutilus) and perch (Perca fluviatilis) LITPRO increased with TP or lake water chlorophyll a (CHLA) for fish >10 cm, suggesting a more littoral distribution with increasing turbidity. Exceptions are pikeperch and bream (Abramis brama). For bream, LITPRO increased significantly with mean lake depth only. For fish ≤10 cm LITPRO showed only a weak relationship to TP, CHLA or depth. In accordance with the TP‐dependent distribution, major changes occurred in the fish community structure during the monitoring period following nutrient loading reduction. A comparison of LITPRO from the first part of the monitoring period (1989–1993) with a subsequent period (1997–2003) for four abundant species showed a significant decline in LITPRO over time for large‐ and small‐sized roach and perch and large rudd. This suggests a fast response in fish distribution to improved water quality. It further demonstrates that fish monitoring in lakes should cover both littoral and pelagic habitats to describe the recovery process.     

Potential direct and indirect effects of climate change on a shallow natural lake fish assemblage

Much uncertainty exists around how fish communities in shallow lakes will respond to climate change. In this study, we modelled the effects of increased water temperatures on consumption and growth rates of two piscivores (northern pike [Esox lucius] and largemouth bass [Micropterus salmoides]) and examined relative effects of consumption by these predators on two prey species (bluegill [Lepomis macrochirus] and yellow perch [Perca flavescens]). Bioenergetics models were used to simulate the effects of climate change on growth and food consumption using predicted 2040 and 2060 temperatures in a shallow Nebraska Sandhill lake, USA. The patterns and magnitude of daily and cumulative consumption during the growing season (April–October) were generally similar between the two predators. However, growth of northern pike was always reduced (?3 to ?45% change) compared to largemouth bass that experienced subtle changes (4 to ?6% change) in weight by the end of the growing season. Assuming similar population size structure and numbers of predators in 2040–2060, future consumption of bluegill and yellow perch by northern pike and largemouth bass will likely increase (range: 3–24%), necessitating greater prey biomass to meet future energy demands. The timing of increased predator consumption will likely shift towards spring and fall (compared to summer), when prey species may not be available in the quantities required. Our findings suggest that increased water temperatures may affect species at the edge of their native range (i.e. northern pike) and a potential mismatch between predator and prey could exist.