Reproduction effort versus the environment; case histories of Windermere perch, Perca fluviatilis L., and pike, Esox lucius L.

The theoretical limits of net reproduction rates for perch, Perca fluviatilis L. and pike, Esox lucius L, have been estimated from the upper and lower limits of fecundity, growth, mortality, age of maturity and biomass of parental stock, observed in Windermere over 40 years. Differences in egg numbers due to changes in fecundity were for perch × 1.5, for pike × 2. Assuming the same mortality, a fast growing cohort would produce more eggs during its lifespan than a slow growing, for perch × 2, for pike × 9. Changes in mortality from high to low resulted in more eggs, for perch × 7, and for pike (where high mortality includes natural and fishing mortality) × 10. Change in age at first maturity from 3 to 2 years was unimportant. Biomass of parental stock varied by × 6 for perch and × 3 for pike, and number of eggs laid varied by x2 for perch and × 5 for pike. The number of recruits at age 2 years varied by × 300 for perch and × 7 for pike. It was concluded that temperature in the first summer of life and predation were of major importance in regulating the number of recruits. Ricker recruitment curves and a simple model showed that perch, but not pike, could produce maximum recruitment from minimum parental stock. For perch, but not pike, compensatory density dependent mortality increased with increased parental stock. It was concluded that responses by the perch and pike populations to a changing environment can not be of sufficient magnitude to prevent wide fluctuations in recruitment.     

Acidification affects the perch,Perca fluviatilis,populations in small lakes,of southern Finland

Synopsis Characteristics of perch were studied in 4 recently acidified lakes in southern Finland. The densities of the populations were 0–250 ha^–1 compared with 1400–3300 ha^–1 in two circumneutral reference lakes. The perch were close to extinction in one acidic lake and dominated by 7 year old fish in two other acidic lakes, suggesting decreased reproduction. Individual fecundity was not reduced by the acidity, but high mortality (close to 100%) of eggs in two acidic lakes indicated recruitment failure. In one of the acidified lakes reproduction had continued resulting in a population dominated by younger fish. However, increased egg mortality, low density, and the resulting high growth rate of perch in this lake were considered to be consequences of the acidity. These findings are the first documentation on the possible decrease of fish populations in Finland due to acid precipitation.     

Population responses of perch (Perca fluviatilis) and roach (Rutilus rutilus) to recovery from acidification in small Finnish lakes

Decreasing trends in atmospheric emissions and acidic deposition during the 1990s have resulted in chemical recovery from acidification in the sensitive surface water systems of southern Finland. Responses of perch and roach populations to the improved water quality were studied in 30 small lakes with the aid of water chemistry monitoring data gathered in 1987–2002 and the data collected from two consecutive periods of gillnet test fishing, 1985–1988 and 2001–2002. In the most acidified lakes, alkalinity and ANC have increased and sulphate and labile aluminium concentrations decreasæed markedly. The response of perch populations to the improved water quality is seen in improved reproduction success, indicated by a higher CPUE in numbers and a lower mean weight. The growth rate of perch has declined as the population density has increased. Roach populations have not recovered in the same way as perch, there being no major changes in NPUE or mean weight. Lower growth rates were, however, observed in the roach populations of all study lakes. The increased perch population density as an obstacle to the recovery of roach populations is discussed. Despite the chemical and biological recovery of the study lakes, the buffer capacity of many headwater lakes is low and the lakes will be sensitive to any increases in acidic deposition in the future.     

Effects of temperature on life history variables in perch

Population structure, recruitment, mortality, life expectancy, age at maturity, gonad development, fecundity, net reproductive rate and energy storage were studied in a perch population exposed to thermal discharge. The experiment was conducted during 1978–1990 in an artificial enclosure at a nuclear power plant on the Baltic Sea coast. Abundance increased after the plant started operating, although the proportion of larger perch dropped to a low level. Recruitment improved, but adult mortality increased. This effect was accentuated as the fishes matured very early and at a very small size, reducing their ability to support a growing gonad in high winter temperatures. During the spawning period, condition dropped to very low levels accompanied by increased mortality. Surviving fish delayed the next spawning by one or more years and reduced their fecundity. Body condition thus improved in large perch at the end of the study period. Life-time fecundity was reduced, and reproductive performance shifted to youner ages.     

Trophic dynamics in a whole lake experiment: size-structured interactions and recruitment variation

Horizontal and vertical heterogeneity as a result of size‐structured processes are important factors influencing indirect effects in food webs. In a whole‐lake experiment covering 5 years, we added the intermediate consumer roach (Rutilus rutilus) to two out of four lakes previously inhabited by the omnivorous top predator perch (Perca fluviatilis). We focused our study on the direct consumption effect of roach presence on zooplankton (and indirectly phytoplankton) versus the indirect effect of roach on zooplankton (and phytoplankton) mediated via effects on perch reproductive performance. The patterns in zooplankton and phytoplankton abundances were examined in relation to population density of roach and perch including young‐of‐the‐year (YOY) perch in the light of non‐equilibrium dynamics. The presence of roach resulted in changed seasonal dynamics of zooplankton with generally lower biomasses in May–June and higher biomasses in July–August in roach lakes compared to control lakes. Roach presence affected perch recruitment negatively and densities of YOY perch were on average higher in control lakes than in treatment lakes. In years when perch recruitment did not differ between lakes as a result of experimental addition of perch eggs, total zooplankton biomass was lower in treatment lakes than in control lakes. Phytoplankton biomass showed a tendency to increase in roach lakes compared to control lakes. Within treatment variation in response variables was related to differences in lake morphometry in treatment lakes. Analyses of the trophic dynamics of each lake separately showed strong cascading effects of both roach and YOY perch abundance on zooplankton and phytoplankton dynamics. Consideration of the long transients in the dynamics of top predators (fish) in aquatic systems that are related to their long life span involving ontogenetic niche shifts is essential for making relevant interpretations of experimental perturbations. This conclusion is further reinforced by the circumstance that the intrinsic dynamics of fish populations may in many cases involve high amplitude dynamics with long time lags.     

Effects of liming on the occurrence and abundance of fish populations in acidified Swedish lakes

Test fishing with multimesh gillnets was performed in 103 acidified Swedish lakes before and 2–4 years after liming. In a subset of 39 lakes additional test fishing was carried out 5–9 years after liming. Taking into account the sampling biases due to differences between water temperature and number of nets used on different sampling occasions, an increase of the total CPUE, the number of species caught and recruitment of dominating species was evident after liming. Decreased recruitment was found for perch (Perca fluviatilis) at a pH below 5.2 and for roach (Rutilus rutilus) at a pH below 6.1. During the acidification phase and 2–4 years after liming acid-tolerant perch dominated the lakes, but when a longer time had elapsed after liming species dominance shifted and acid-sensitive planktivorous species increased in CPUE while perch decreased.     

The potential for biomanipulation using fry communities in a lowland reservoir: concordance between water quality and optimal recruitment

The fry community in a temperate lowland reservoir was monitored for seven years. The variation in reproductive success of the dominant perch and cyprinids was correlated with the variation of the water level. During summer the main food of perch wasDaphnia. In the year with the highest density of perch, a decline in the density of cladocerans and in the percentage ofDaphnia eaten was observed. This resulted in low stomach fullness and poor fry growth. Simultaneously, the amount of phytoplankton increased. An optimal recruitment curve was found for maintaining water quality with optimal recruitment of fish stocks, assuming that a high rate of fry growth is essential for high survival during winter. Regulation of fry densities can be achieved by the manipulation of water levels during the reproductive and early ontogeny period.     

Length-dependent changes in egg size and fecundity in females, and brooded embryo size in males, of fork-tailed catfishes (Pisces: Ariidae) from the Sepik River, Papua New Guinea, with some implications for stock assessments

Data suggest that mature egg weight is positively correlated to female parent length in all five species of fork-tailed catfish studied. Embryo weight is positively correlated with the length of the male mouthbrooding parent in the four species where data are available. Non-random mate pairing is probably between fish of equivalent size. Fecundity appears to be linearly related to female fish length in all species. There is no significant correlation between fecundity and female weight, probably because egg size increases with fish size. Low fecundities and breeding behaviour suggest that recruitment is likely to be highly density-dependent and the stocks vulnerable to increased mortality (fishing). Changes in egg size with fish size may account for deviations from a cube relationship between fecundity and fish length in other species. The relevance of this to other fish stock assessments is discussed. Attention is drawn to possible changes in egg size with fish length which could affect recruitment in fished stocks, depending on the specific relationship and the length at which mature fish are caught.     

Interactions between year classes in the benthic amphipod Monoporeia affinis: effects on juvenile survival and growth

Summary The effect of 1-year-old Monoporeia (=Pontoporeia) affinis on the survival and growth of young of the year was studied in laboratory experiments. Amphipods were kept in jars with sediment and a continuous supply of cooled water for 3 months. Adults or juveniles were added to a control density of juveniles. Juvenile mortality increased at higher total densities, and was greater when adults were present. The mean length and dry weight of juveniles decreased at higher densities, but adults did not have a greater effect than juveniles. These density-dependent effects are probably caused by competition for food within and between year classes. Thus, a high abundance of juveniles or adults could reduce the recruitment of juveniles into the adult year-class the following year, and the suppression of juvenile growth could lower fecundity. The results of this experiment support the hypothesis, inferred from field data from the Baltic Sea and Swedish lakes, that intraspecific interactions contribute to fluctuations in the abundance of populations of M. affinis.     

Perch,Perca fluviatilis L., in Small Lakes: Relations between Population Characteristics and Lake Acidity

Perch population characteristics of small lakes were examined with a special reference to lakes which have acidified recently due to atmospheric deposition of air pollutants. The population density and biomass of perch were higher in an acid (pH 4.5) clear water lake with low aluminium concentration than in recently acidified (pH 4.3–4.7) clear water lakes with higher aluminium levels. The structure of perch population in an acid (pH 4.4) humic lake was similar to recently acidified clear water lakes. The population density and the biomass of perch were significantly higher in 6 lakes with pH>5.0 than in 6 lakes of pH<5.0 whereas the mean age and length at a given age were higher in the more acid lakes.     

Development of fish communities in lakes after biomanipulation

Biomanipulation measures in the Netherlands are usually a combination of a drastic fish stock reduction and an introduction of pike fingerlings. In three small shallow lakes (Noorddiep, Bleiswijkse Zoom and Zwemlust) these measures resulted in a clear water state and the development of macrophytes. After the measures the fish community developed differently because of the new physical and biological conditions. Results of lake Noorddiep and lake Bleiswijkse Zoom showed that the fish community became more divers. Bream and carp became less dominant and were partly replaced by roach and perch. The importance of the main predator pike-perch was strongly reduced and replaced by pike and perch. The share of piscivorous fish in the total fish stock increased at all sites. The recruitment of young-of-the-year was similar or even higher in the clear overgrown areas than in the turbid water before the measures, but the recruitment of young-of-the-year to older fish differed between the species. Predation by pike and perch could not control the young-of-the-year cyprinids, but their predation may have contributed to the shift from bream to roach, because of selective predation on bream in the open water, while roach was hiding in the vegetation. The macrophytes provide new refugia and feeding conditions that favour roach and perch, but offer relatively poor survival conditions for bream and carp.     

The population dynamics of pike,Esox lucius,and perch,Perca fluviatilis,in a simple predator-prey system

Synopsis The population dynamics and predator-prey relationship of pike, Esox lucius, and perch, Perca fluviatilis, were examined in simple fish communities in two adjacent shallow lakes, Lochs Kinord and Davan, Deeside, Scotland. Few perch survive to age 3 but Z is low for fish > 3 years and perch live up to 17 years. Population fecundity remained relatively high and constant in perch because of the multi-age spawning stock and the presence of older more fecund perch. Growth rates of perch in both lochs are relatively high as a consequence of low stock abundance. The N, B, and P of adult perch were unusually low. The age range of pike, and N, B, P, and growth were in the range of values reported elsewhere. There was little variation in the strength of pike year classes and the importance of cannibalism and low occurrence of alternative prey in the lochs suggest that the populations were self-regulating. Cannibalism by adults was responsible for most of mortality in perch larvae, and predation by pike and adult perch was responsible for the majority of juvenile losses. This conclusion is supported by the high biomass ratios of pike:juvenile perch of 1.0–30.8. While the number of adult fish was almost equal, the biomass of adult pike was 2–3 × that of perch in Kinord and 6 × in Davan. In L. Kinord, where year class strength was stable, high predation pressure from perch and pike reduced perch abundance rather than eliminated year classes. Perch year classes fluctuated in abundance in L. Davan and were eliminated in the first summer in two sampling years. The pike, and particularly the perch populations, have features characteristic of fish communities in unperturbed ecosystems: namely, a wide range of age classes, stability in biomass with variation dampened by longevity, and low production.     

Overwinter changes in mass and lipid content of Perca fluviatilis and Gymnocephalus cernuus

The body condition, lipid reserves and mortality of 0 and 1 year‐old perch Perca fluviatilis and ruffe Gymnocephalus cernuus , sampled during the winter in Lake Constance, Germany, were compared. Length‐frequency analyses did not provide evidence for overwinter mortality in either species. The fresh and dry mass of perch as well as their lipid contents decreased during winter, while ruffe were heavier and contained more lipid at the end of the winter. The superior performance of ruffe was mainly attributed to its sensory capabilities, which allowed it to ingest zoobenthos throughout the winter, while the zooplankton feeding of perch was constrained by low light levels. In lakes that undergo a process of re‐oligotrophication, this advantage of ruffe over perch may be even more pronounced, since lower food supply during the growth season and thus lower fish lipid content at the start of winter is probably better tolerated by ruffe than by perch.     

State-dependent invasion windows for prey in size-structured predator-prey systems: whole lake experiments

1. In size-structured communities where individuals grow in size over their life cycle, interactions between species will shift between competitive and predatory interactions depending on size relationships. The outcome of interactions will subsequently depend on the strength of competitive and predatory interactions, respectively. 2. In a whole lake experiment including four experimental lakes, it was tested under which conditions the competing prey, roach Rutilus rutilus, could successfully recruit into systems previously occupied by the predator, perch Perca fluviatilis. Two replicated introduction experiments were carried out 3 years apart. 3. Roach were able to successfully recruit into three of the four experimental lakes of which two were also inhabited by the top predator pike Esox lucius. Resource levels were unrelated to whether roach could successfully recruit into the systems as recruiting roach in all years were feeding close to their maximum rate. 4. High population fecundity of roach and low predation pressure by perch combined were necessary ingredients for successful recruitment and the presence of only one of these conditions did not result in successful recruitment. 5. It is hypothesized that, although roach were able to successfully recruit into one lake with only perch present in addition to the two lakes that also inhabited pike, long-term coexistence of roach and perch depends on the presence of another top predator (e.g. pike) selectively preying on perch. This hypothesis was supported by data on co-occurrence of perch and roach in different lakes. 6. Overall, the results are in accordance with expectation of size-structured life-history omnivory theory suggesting that coexistence between top predator and intermediate consumer is fragile.     

Functional response in habitat selection and the tradeoffs between foraging niche components in a large herbivore

How herbivore behaviour is influenced by changes in resource levels is central for understanding trophic interactions. We examined whether foraging tradeoffs change with food levels by comparing habitat selection and space use within and between two neighbouring, predator‐free Svalbard reindeer populations. The populations faced different food levels due to contrasting grazing history. Summer resource selection in radiocollared females was assessed by a multi‐dimensional niche approach based on habitat variables obtained from a satellite image (e.g. the normalised difference vegetation index, NDVI) and a digital terrain model. The population at the overgrazed Brøggerhalvøya faced overall lower plant cover, biomass and primary productivity (i.e. lower NDVI) than the population at Sarsøyra. At Brøggerhalvøya, most reindeer selected for productive habitat when choosing home range and patches within the home range. In contrast, habitat selection at Sarsøyra was more affected by abiotic conditions such as moisture, which may influence plant quality. Here, reindeer used patches with even less biomass than the average reindeer at the poorer Brøggerhalvøya. Such a difference in habitat preference with different habitat availability (a functional response in habitat selection) probably reflected increased selection for high‐quality forage at the expense of high forage quantity at Sarsøyra. Accordingly, a negative relationship between habitat productivity and home range size was only present across individuals within Brøggerhalvøya, where forage quantity was the important foraging niche component. Individuals having poor (and large) home ranges apparently could not compensate for this by higher patch selectivity compared to individuals with richer home ranges. The results indicate changes in foraging tradeoffs at contrasting resource levels and that strong interactions occur between habitat selection, space use and the foraging niche structure in the absence of predation.     

Factors influencing changes in mercury concentrations in lake water and yellow perch (<Emphasis Type="Italic">Perca flavescens</Emphasis>) in Adirondack lakes

Over the past 20+ years, fish with elevated concentrations of mercury (Hg) have been observed in remote lake districts, including the Adirondack region of New York. Across eastern North America studies have also reported a negative correlation between fish Hg concentration and lake pH. Recent controls in emissions of sulfur dioxide (SO₂) have resulted in some improvement in the acid–base status of acid-impacted surface waters including Adirondack lakes. In addition, there has been an apparent decrease in atmospheric Hg deposition. A synoptic survey of 25 lakes in the Adirondacks was conducted in 1992–1993 to analyze spatial patterns of Hg in the water column and yellow perch (Perca flavescens). The same cluster of 25 lakes was resurveyed in 2005–2006 to evaluate if changes in lake concentrations of Hg species or fish Hg have occurred. We observed a varied response of changes in water chemistry and fish Hg concentrations. In twelve of the resurveyed lakes the yellow perch had lower Hg concentrations, six lakes had yellow perch with higher Hg concentrations, and in seven lakes yellow perch Hg concentrations did not change significantly (α = 0.05). Four variables appear to influence the change in yellow perch Hg concentrations in the Adirondacks: watershed area, elevation, change in pH, and change in fish body condition. We hypothesize that as the acidity in lakes is attenuated, the lakes may become more productive and/or water quality conditions less stressful to fish leading to increasing fish body condition. As fish body condition improves, fish exhibit “growth dilution” of tissue contaminants leading to lower fish Hg concentrations.     

The monitoring of biological effects: the separation of natural changes from those induced by pollution.

An added mortality rate of eggs, larvae and juveniles of fish populations, or impact, is assumed to be density independent. The total mortality from hatching to recruitment is represented by the fecundity, and any increment in density independent mortality implies a decrement in density dependent mortality. At high stock the condequence is an increase in stock towards a position of less resilience: at low stock less resilience is found with a decrease in stock. In general impact generates a shift of K-strategy, the self-stabilizing strategy, to r-strategy, and opportunistic one. In a fish population very little impact should be tolerated at low stock because it would prevent recovery to a management objective such as maximum sustainable yield. At high stock, impact may generate more stock at an unknown risk.     

Rapid and unexpected effects of piscivore introduction on trophic position and diet of perch (Perca flavescens) in lakes recovering from acidification and metal contamination

1. Yellow perch (Perca flavescens) are often the only surviving fish species in acidified lakes. We studied four lakes along a gradient of recovery from acidification and that had different food web complexities. All had abundant yellow perch, two had low piscivore abundance, one had a well‐established piscivore population and one was manipulated by introducing piscivorous smallmouth bass (Micropterus dolomieu). We hypothesised that there would be strong effects on perch abundance, behaviour and diet induced by the presence of piscivores. 2. In the manipulated lake, the bass reduced yellow perch abundance by 75% over a 2‐year period. Concomitantly, perch use of the pelagic habitat fell from 48 to 40%. 3. In contrast to findings from less disturbed systems, yellow perch in the littoral zone of the manipulated lake did not strongly shift from zooplankton to benthic food sources after the arrival of piscivores. Diet analysis using stable carbon isotopes revealed a strong continued reliance on zooplankton in all lakes, independent of the degree of piscivory. The failure to switch to benthos in the refuge area of the littoral zone is most likely related to the depauperate benthos communities in these formerly acidified lakes. 4. Yellow perch in lakes recovering from acidification face a considerable ecological challenge as the necessary switch to benthic diet is hindered by a low abundance of benthos. The arrival of piscivores in these recovering lakes imposes further restrictions on perch access to food items. We infer that future recovery of perch populations (and higher trophic levels) will have to be preceded by the re‐establishment of diverse benthic macroinvertebrate communities in these lakes.     

Reproductive pattern of the freshwater prawn Pseudopalaemon bouvieri (Crustacea,Palaemonidae) from hypo-osmotic shallow lakes of Corrientes (Argentina)

Pseudopalaemon bouvieri undergoes complete abbreviated development. The reproductive cycle (proportion and size of the sexually mature population and juvenile recruitment), fecundity and egg size of this prawn were examined in three subtropical shallow lakes. The reproductive cycle was seasonal; gonadal maturation occurred during the winter, ovigerous females were abundant in the spring and breeding occurred at the end of spring. Females produced small numbers of eggs (9–55) of relatively large sizes (1.0–2.1 mm). The proportion of ovigerous females with respect to the total number of females, the fecundity and egg size differed among the lakes according to the trophic state of the environments. Pseudopalaemon bouvieri has a reproductive strategy similar to other Palaemonidae species that inhabit nutrient-poor inland waters.     

How many fish populations in Finland are affected by acid precipitation?

Synopsis The number of fish populations affected or lost from small lakes in southern and central Finland due to acid precipitation is estimated. Tolerance limits (pH and labile aluminum) of common fish species were obtained from a fish status survey of 80 lakes. These tolerance values were used to estimate the proportion of affected lakes from the water chemistry data of 783 statistically selected lakes. The proportion of anthropogenically acidified lakes was estimated by calculating pre-acidification pH and aluminum concentrations of the lakes, using a steady-state model based on water chemistry. The number of fish populations for which acidification has affected growth or population structure was estimated at between 2200 and 4400. Out of these, the number of fish populations that have disappeared due to acid precipitation would be about 1000–2000. Almost 60% of the affected or lost populations are roach, Rutilus rutilus, the most sensitive of the common fish species in small lakes in southern and central Finland. Less than 15% of the damaged population is European perch, Perca fluviatilis, the most common species. This is due to the substantially higher tolerance of perch to acidified water in comparison with roach.