Young-of-the-year Perch Research Articles

Diet overlap between young‐of‐the‐year perch, Perca fluviatilis L., and burbot, Lota lota (L.), during early life‐history stages

Abstract – The diet overlap between young‐of‐the‐year (YOY) perch and burbot in the pelagic zone of Lake Constance during spring and summer was investigated in relation to gape size limitation. Because perch were larger and grew faster than burbot during their early life history, perch overcame gape size limitation for various zooplankton taxa earlier than burbot. The interspecific diet overlap between perch and burbot decreased continuously until June, but increased slightly, when burbot became able to feed on large daphnids by the beginning of July. All zooplankton taxa could be found within perch stomachs by the middle of June, when perch overcame gape size limitation for large cladocerans. However, there was an increasing tendency for individual diet specialisation of perch, as the similarity between individual perch stomach contents decreased. In contrast, the similarity between individual burbot stomach contents remained at almost 50% until the end of August, indicating that all burbot rely on cyclopoid copepods during their entire pelagic life‐history stage. Because by July YOY perch are more abundant by one order of magnitude in the pelagic zone than burbot, YOY perch may be more affected by intraspecific competition than by interspecific competition with burbot. Burbot, on the other hand, may evade strong competition with YOY perch by performing diel vertical migrations, thus being restricted to feed on migrating zooplankton prey.

Formation of morphological defences in response to YOY perch and invertebrate predation in two Daphnia species coexisting in a mesotrophic lake

This study examined the formation of morphological defences by two coexisting Daphnia species, the large-sized D. pulicaria (2 mm) and the small-sized D. mendotae (1.4 mm), in response to the presence of young-of-the-year (YOY) yellow perch (Perca flavescens) and invertebrate predators (Chaoborus, Leptodora) during summer in a mesotrophic lake. We hypothesized that due to differential size-selective predation risk by YOY fish and invertebrates, the large-sized and the small-sized Daphnia species would show different morphological responses to predation threats. We followed changes in two morphological traits (relative length of the tail spine in D. pulicaria and of the helmet in D. mendotae) among different periods during summer according to YOY fish and invertebrate predation. We defined four YOY fish predation periods based on the presence of YOY perch in the pelagic zone of the lake and the relative abundance of Daphnia preys in their gut contents, and two invertebrate predation periods based on exclusive or mutual occurrence of the invertebrate predators. The large-sized (D. pulicaria) and the small-sized (D. mendotae) species showed different morphological responses to YOY fish and invertebrate predators, respectively. The tail spine ratio of the juveniles and adults of D. pulicaria did not change in response to YOY fish predation or to invertebrate predation. A gradual increase in the helmet ratio was observed in the small-sized D. mendotae over the summer period. This change was related to the co-occurrence of the invertebrate predators (Chaoborus and Leptodora) and to YOY fish predation. The warmer temperature cannot be accounted for helmet elongation since it was constant across depths, and not related with the co-occurrence of D. mendotae and YOY perch.

Alternative antipredator responses of two coexisting Daphnia species to negative size selection by YOY perch

Our study showed for the first time in nature that two coexisting Daphnia adopted alternative life history and behavioural strategies to cope with negative size-selection predation by gape-limited young-of-the-year (YOY) perch. We evaluated the phenotypic plasticity in life history and behavioural traits of two coexisting Daphnia species, D. pulicaria (2 mm) and D. galeata mendotae (1.4 mm), in response to seasonal changes in predation by YOY yellow perch (Perca flavescens) in a mesotrophic lake. We expected that the large-sized D. pulicaria, the most likely subjected to sizeselective predation by YOY perch, will show stronger antipredator responses than the small-sized D. galeata mendotae. To test this hypothesis, we examined changes in life history and behavioural traits in juveniles and adults of both species during four YOY fish predation periods that were selected based on the presence of YOY perch in the pelagic zone and the relative abundance of Daphnia prey in their gut contents. Our study supports the scenario of negative size-selective predation by gape-limited YOY perch on both Daphnia species. The electivity index indicated that no daphnids with a body length .1.75 mm were predated by YOY yellow perch. Coexisting Daphnia exhibited phenotypic plasticity in their antipredator defenses based on their vulnerability to seasonal changes in size-selective predation of YOY perch. Juvenile Daphnia were the targeted prey and they responded by a decreased body length. Behavioural defenses were the dominant strategy used by both adult Daphnia populations to withstand high predation. A decreased size at maturity was not employed by Daphnia, except at the very end of the predation period. Behavioural defenses are short-term strategy adopted to avoid predation. Both antipredator defenses became unnecessary expenses and were no longer sustained after the predation period.

Disruption of the hypothalamo-pituitary-interrenal axis in 1+ yellow perch (Perca flavescens) chronically exposed to metals in the environment

Although it has been reported that adult yellow perch (Perca flavescens) chronically exposed to metals in the environment exhibit endocrine impairment characterized by blunted cortisol secretion, little is known about the vulnerability of early life stages. Young-of-the-year (YOY) and 1+ yellow perch were captured, subjected to a standardized stress test or adrenocorticotropic-hormone stimulation in lakes situated along a contamination gradient of Cd, Cu, and Zn in the mining region of Abitibi, Quebec. For the first time, whole-body cortisol concentrations were measured. The 1+ fish with elevated whole-body Cd, Cu, and Zn concentrations had an impaired capacity to respond to an acute stress challenge. Although YOY perch had similar whole-body Cd concentrations to 1+ perch, no effects on physiological status were detected in relation to body burdens of metals. Metal contamination did not affect whole-body thyroid-hormone concentrations, condition factor, or hepatosomatic index in 1+ or YOY perch. These results indicate that effects of Cd, Cu, and Zn on the functional integrity of the hypothalamo-pituitary-interrenal axis in yellow perch are detectable after only 1 year of environmental exposure.

Individual diet specialization, niche width and population dynamics: implications for trophic polymorphisms

SummaryWe studied a perchPerca fluviatilisL. population that during a 9‐year period switched between a phase of dominance of adult perch and a phase dominated by juvenile perch driven by cannibalism and intercohort competition. We investigated the effects of these population fluctuations on individual diet specialization and the mechanisms behind this specialization.Due to cannibalism, the survival of young‐of‐the‐year (YOY) perch was much lower when adult perch density was high than when adult perch density was low.Both the individual niche breadth (if weighed for resource encounter) and the population niche breadth were highest when adult population density was high and, consequently, individual specialization was highest at high adult perch densities.When adult perch density was low, the abundances of benthic invertebrate and YOY perch were high and dominated the diet of adult perch, whereas the density of zooplankton was low due to predation from YOY perch. At high perch densities, benthic invertebrate abundance was lower and zooplankton level was higher and some perch switched to feed on zooplankton.Our results show that individual specialization may fluctuate with population density through feedback mechanisms via resource levels. Such fluctuations may have profound implications on the evolution of resource polymorphisms.

Simultaneous Sv and TS measurements on Young-of-the-Year (YOY) freshwater fish using three frequencies

Abstract In autumn, the fish population above the thermocline in Lake Annecy mainly comprises young perch (Perca fluviatilis) of the year. The fish are distributed in schools during the day and as scattered individual fish targets at night. Measurements of volume-backscattering strength and target strengths (TS) were carried out in a synchronous way using three echosounders operating at three frequencies (70, 120, and 129 kHz), with different characteristics (split beam, dual beam, beam shape, pulse length, etc.). Target-strength values show variability from one elementary sampling unit to another and from one device to another, but the mean global TS values are similar, independently of the frequency. The volume-backscattering strengths measured on precise schools by the three acoustic devices give significantly similar results. Acoustic measurements on YOY perch are completely independent of the frequency and the characteristics of the echosounders.

Diel vertical and horizontal distribution of crustacean zooplankton and young of the year fish in a sub-alpine lake: an approach based on high frequency sampling

Understanding the spatial dynamics of predators and their prey is one of the most important goals in aquatic ecology. We studied spatial and temporal onshore-offshore distribution patterns in young of the year (YOY) Eurasian perch (Perca fluviatilis) and crustacean zooplankton (Daphnia hyalina, Cyclops prealpinus) along a transect in Lake Annecy (France). Our study represents a first attempt at coupling hydroacoustic fish survey and high frequency zooplankton recording to assess simultaneously the large-scale distribution patterns of YOY fish and their zooplankton prey over a diel cycle (day, dusk and night sampling). We hypothesized that the spatial distribution of zooplankton could be shaped by both anti-predator behaviour (horizontal and vertical migrations) and predation losses. Fish biomass, size structure and diet were assessed from split-beam echosounding and net trawling samples, whereas crustacean abundances were estimated with a small modified Longhurst-Hardy continuous plankton recorder. We evaluated the diel changes in the spatial distribution patterns of fish and zooplankton and determined the overlap between their distributions. Fish biomass was dominated by YOY perch in upper warmer layers and salmonids (Coregonus lavaretus and Salvelinus alpinus) in the colder and oxygenated deep layers. YOY perch were aggregated in dense schools in the epilimnion during the day and dispersed at night. Fish biomass was distributed along a strong increasing onshore-offshore gradient at night, whereas crustacean prey showed a decreasing gradient. This onshore-offshore negative gradient in crustacean distribution, expressed on a shorter scale during the day, shifted toward the surface waters at night. A distinct kinetic of diel vertical migration (DVM) patterns was exhibited by daphnid and cyclopoid populations and resulted in distinct vulnerability to perch predation. Spatio-temporal distribution of crustaceans in Lake Annecy during the diel cycle study was probably shaped both by predation loss to YOY perch and by anti-predator behaviour (DVM, DHM) by zooplankton. The implications for fine-scale studies of fish-zooplankton interactions are discussed.

Cannibalism and Competition in Eurasian Perch: Population Dynamics of an Ontogenetic Omnivore

In many cannibalistic populations, cannibals share resources with their victims, leading to a size-dependent mixture of cannibalistic and competitive interactions. We analyze the impacts of such interactions on the population dynamics of Eurasian perch (Perca fluviatilis) by considering effects of intercohort competition, habitat heterogeneity, habitat selection, and energy gain made by cannibals. Over a six-year period, we measured mortality and recruitment patterns, individual growth, body condition, resource levels, diets, and habitat use as functions of density for an allopatric perch population in a low-productivity lake. During the course of the study, two major die-offs took place, selectively affecting larger cannibalistic individuals, followed by several years of successful recruitment of young fish. Habitat use of perch ≥2 yr old was density dependent, and these fish used only the inshore region at low densities. The appearance of young fish followed the die-offs of cannibalistic perch and their subsequent absence from the offshore area, both of which decreased cannibalism on pelagic recruits. Whereas die-offs of larger perch could not be related to competition with young-of-the-year (YOY) perch, evidence for a competitive impact of YOY perch on Age-1 perch was present due to substantial food overlap. A strong depression in pelagic zooplankton was observed during summer in years with strong recruitment, which resulted in reduced consumption of zooplankton, slow growth, and reduced body condition in Age-1 perch and suggested high mortality of Age-1 perch in autumn. Age-1 perch did not appear to profit substantially from cannibalism on YOY perch because of the short time period that they could efficiently prey on YOY perch. The few larger perch that survived the die-offs gained substantial energy from cannibalism in years with strong recruitments, which increased both growth rates and per capita fecundity. Size-dependent intercohort competition may have strong impacts on cannibal–victim interactions when victims share resources with cannibals. Furthermore, habitat heterogeneity, combined with habitat selection, may limit the extent to which cannibals have a stabilizing effect on population dynamics. Finally, the energy gained by cannibals may have important consequences on population dynamics as this energy is allocated into new recruits.

CANNIBALISM AND COMPETITION IN EURASIAN PERCH: POPULATION DYNAMICS OF AN ONTOGENETIC OMNIVORE

In many cannibalistic populations, cannibals share resources with their victims, leading to a size-dependent mixture of cannibalistic and competitive interactions. We analyze the impacts of such interactions on the population dynamics of Eurasian perch (Perca fluviatilis) by considering effects of intercohort competition, habitat heterogeneity, habitat selection, and energy gain made by cannibals. Over a six-year period, we measured mortality and recruitment patterns, individual growth, body condition, resource levels, diets, and habitat use as functions of density for an allopatric perch population in a low-productivity lake. During the course of the study, two major die-offs took place, selectively affecting larger cannibalistic individuals, followed by several years of successful recruitment of young fish. Habitat use of perch ≥2 yr old was density dependent, and these fish used only the inshore region at low densities. The appearance of young fish followed the die-offs of cannibalistic perch and their subsequent absence from the offshore area, both of which decreased cannibalism on pelagic recruits. Whereas die-offs of larger perch could not be related to competition with young-of-the-year (YOY) perch, evidence for a competitive impact of YOY perch on Age-1 perch was present due to substantial food overlap. A strong depression in pelagic zooplankton was observed during summer in years with strong recruitment, which resulted in reduced consumption of zooplankton, slow growth, and reduced body condition in Age-1 perch and suggested high mortality of Age-1 perch in autumn. Age-1 perch did not appear to profit substantially from cannibalism on YOY perch because of the short time period that they could efficiently prey on YOY perch. The few larger perch that survived the die-offs gained substantial energy from cannibalism in years with strong recruitments, which increased both growth rates and per capita fecundity. Size-dependent intercohort competition may have strong impacts on cannibal–victim interactions when victims share resources with cannibals. Furthermore, habitat heterogeneity, combined with habitat selection, may limit the extent to which cannibals have a stabilizing effect on population dynamics. Finally, the energy gained by cannibals may have important consequences on population dynamics as this energy is allocated into new recruits.

Resource limitation during early ontogeny: constraints induced by growth capacity in larval and juvenile fish.

The presence of and mechanisms behind density-dependent growth and resource limitation in larval and juvenile stages of organisms with high mortality such as fish are much debated. We compare observed consumption and growth rates with maximum consumption and growth rates to study the extent of resource limitation in young-of-the-year (YOY) roach (Rutilus rutilus) and perch (Perca fluviatilis). Diet, habitat use, consumption rate and growth rate were measured under varying YOY fish densities over 2 years in four lakes. In the first year, YOY roach and perch were studied under allopatric conditions. Experimental addition of perch roe in the second year also allowed study of YOY of the two species under sympatric conditions in two of the lakes. The diet of YOY roach was dominated by cladoceran zooplankton and YOY roach habitat use was restricted to the shore region in both years. This restricted habitat use did not involve any cost in foraging gain in the first year as consumption and growth rates were very close to maximum rates. During the second year, when the two species coexisted, resources were limited in late season, more so in the littoral than in the pelagic habitat in one lake while the reverse was the case in the other lake. The diet of YOY perch was also dominated by zooplankton, and with increasing perch size the proportion of macroinvertebrate prey in the diet increased. After hatching, YOY perch first utilized the pelagic habitat restricting their habitat use to the shore after 1 to several weeks in the pelagic zone. During the larval period, perch were not resource limited whereas juvenile perch were resource limited in both years. The fact that YOY perch were more resource limited than YOY roach was related to the higher handling capacity and lower attack rate of perch relative to roach, rendering perch more prone to resource limitation. Estimates of resource limitation based on consumption rates and growth rates yielded similar results. This supports the adequacy of our approach to measure resource limitation and suggests that this method is useful for studying resource limitation in organisms with indeterminate growth. Our results support the view that density-dependent growth is rare in larval stages. We suggest that density-dependent growth was absent because larval perch and roach were feeding at maximum levels over a wide range of larvae densities.

Interactions among Size-Structured Populations in a Whole-Lake Experiment: Size- and Scale-Dependent Processes

Interactions in size-structured populations are characterized by a mixture of predatory and competitive interactions dependent on the size of the individual organism. We analyzed this mixture of size-structured interactions for a species constellation consisting of perch (Perca fluviatilis) and roach (Rutilus rutilus) in a replicated whole lake experiment over 4 yr. Roach are preyed upon by large perch, but at the same time compete with small perch for zooplankton. Predictions regarding the effects of roach on perch performance and resource dynamics in the whole-lake experiment were based on results from previous pond and enclosure experiments carried out over short (months) time periods. Variables measured in the whole-lake experiment included both individual level parameters (diet and growth of perch) as well as population level parameters (mortality, population numbers and size structures of perch, abundance and biomass of zooplankton and benthic macroinvertebrates). The population size of perch ≥ 2 yr old decreased to less than 10% of the pre-treatment levels in treatment lakes after the introduction of roach and remained low over the whole study period. The mortality in perch one-year-old and older increased with size. Larger perch had a higher growth decrease than smaller perch, but also the individual growth rate of young-of-the-year (YOY) perch was lower in treatment lakes than in control lakes. YOY perch were almost excluded during the winter and spring following the roach introduction. The few perch of this year class that survived had the following years a higher growth than the corresponding year class in control lakes. This could be related to an increased availability of predator-sensitive macroinvertebrates in treatment lakes. Perch in treatment lakes fed to a larger extent on macroinvertebrates and less on pelagic zooplankton than perch in control lakes. As expected, zooplankton abundances decreased in treatment lakes the year following the roach introduction, but thereafter zooplankton abundances were higher in treatment lakes due to the absence of perch recruitment in these lakes. No incidence of perch predation on roach was recorded during the study period. We attribute this to the spatial scale dependent escape ability and habitat use of vulnerable size classes of roach. YOY perch had a stronger impact on between-year variation in zooplankton than YOY roach and this can be related to the higher foraging (handling) capacity of the former and the restricted habitat use of the latter. Individual level parameters (diet, growth) had a higher statistical power than population level parameters (abundance, biomass, mortality), and small-scale experiments successfully predicted a higher proportion (81%) of the individual level parameters. However, the lower success in predicting population level responses (38%) was directly connected to a failure to predict individual level parameters (large perch diet and growth). Our results suggest that the small spatial scale was the major limitation on the predictive ability of the small-scale experiments.