<p>I studied the effects of temperature, pH, competition and predation on Eurasian perch (<i>Perca fluviatilis</i>) in 30 lakes in Norway during 1981-2001. The study lakes were situated in two different areas in southern Norway; four lakes in Aust-Agder county in southernmost Norway were explored during 1981-1984 and 26 lakes in Hedmark county in south-eastern Norway were investigated during 1992-2001. The study lakes varied considerably in pH, temperature, fish species composition, and perch abundance and size composition. In addition to field surveys, behavioural studies of perch were conducted at Karlstad University in 2006-2007.</p><p>The field studies revealed that temperature affected recruitment of perch as strong year-classes of perch generally occurred in summers with high temperatures. Temperature also affected perch behaviour as indicated by the low gillnet catches (CPUE) of perch atlow temperature. This effect on CPUE was also supported by results from the aquaria experiments, where swimming and feeding activity of perch was low at low temperature. In a study of four lakes, growth was positively related to temperature in the lake with an allopatric perch population, but not in three lakes where perch occurred sympatrically with roach.</p><p>pH also affected recruitment. In the four lakes in Aust-Agder, one strong year-class of perch occurred in all lakes in a year with especially high pH in spring and early summer. Adult mortality was also affected by pH, as old perch were less abundant in lakes with late spring pH=5.5-5.8 than in lakes with pH<5.5 and pH>5.8. The size and growth of adult perch were negatively affected by low pH, whereas abundance of large, potentially predatory perch was positively related to pH.</p><p>The field studies indicated that roach influence perch populations. When coexisting with roach, perch were mainly littoral. In lakes where roach dominated (by number), there was no growth – temperature correlation, but there was such a correlation in lakes without roach. In lakes with sympatric roach, age-specific weight of perch and the growth of 2+ perch were negatively related to the proportion of roach in the gillnet catches. In the aquaria experiments, swimming and feeding activity of perch were lower than that of roach at all temperatures tested, and the difference was most pronounced at 4 and 8 °C. The aquaria experiments indicated that perch had a lower feeding efficiency and that they generally occupied positions closer to the bottom than roach.</p>

<p>Biological diversity is controlled by an array of factors and processes all active at different spatial and temporal scales. Regional factors control what species are available to occur locally, whereas the local factors determine what species are actually capable of colonizing the locality.</p><p>I have investigated how these local and regional factors affect species richness and diversity, mainly of fish in Swedish lakes and in order to assess the impact of dispersal mode one study on bacteria was also performed. In addition, potential first steps towards speciation were investigated in perch (<i>Perca fluviatilis</i>) from two different habitats. </p><p>Fish species richness and diversity were found to be regulated by history, dispersal limitation and the local environment. In addition, striking similarities were found in the control of community composition for fish and bacteria. Both were regulated by nearly equal parts regional and local factors. The study of morphological and genetical variation in perch (<i>Perca fluviatilis</i>) revealed genetic differentiation at small spatial scales, suggesting that genetic differences can evolve between groups at strikingly small spatial scales, which might have implications for speciation in a long time perspective. </p><p>Based on these findings I conclude that space and time matter. Space has the potential to isolate sites. And both dispersal and local extinctions, it seems, might take a long time, as effects of the last ice-age can still be seen on the contemporary fish community richness and composition.</p>

Recent studies show that populations of the freshwater isopod Asellus aquaticus L. can rapidly become locally differentiated when submerged stonewort (Chara spp.) vegetation expands in lakes. In the novel Chara habitat, isopods become lighter pigmented and smaller than in the ancestral reed stands. In this study, I used laboratory experiments to investigate if selective predation by fish could be a possible explanation for these phenotypic changes. Predation from fish is generally considered to be a strong selective force on macroinvertebrate traits. In the first experiment I measured perch (Perca fluviatilis L.) handling time for three size classes of Asellus to see which size of those that would be the most profitable to feed upon. No difference in handling time was detected between prey sizes, hence the largest size would be the most beneficial to feed upon. In a second experiment I let perch feed on a mixture of Asellus phenotypes in aquaria manipulated to mimic the substrates in either the Chara or the reed habitats. Remaining isopods were significantly smaller and lighter pigmented in the fish aquaria than in the controls, showing that the perch preferred to feed on large and dark individuals. In the Chara habitat, selection on isopod pigmentation was according to what could be expected from background matching, but in the reed habitat selection was quite the opposite. These results support the hypothesis that predation from fish is a strong selective force behind the rapid local adaptation seen in Asellus populations in the novel Chara habitat.

Trout-perch, Percopsis omiscomaycus, were collected during the sample months June through September, 1973, in southern near-shore waters of Lake Michigan near Michigan City, Indiana. Three transects were sampled at depths of 1, 5 and 15 m using an otter trawl and a nylon bag seine. Fish were collected mainly at midnight because of diurnal migration and feeding demonstrated by trout-perch.Food habit analysis showed Chironomus spp. and Pontoporeia affinis to be the major food items of the trout-perch. Other organisms of lesser importance as food include: Eurycercus lamellatus, Eurytemora affinis, Chironomid pupae and alewife eggs, Alosa pseudoharengus.A combined monthly analysis of trout-perch food habits showed zooplankton and alewife eggs as important food items in, June decreasing.in importance throughout the remaining sample months. Amphipoda, primarily Pontoporeia affinis, was of greatest importance in June decreasing in percent volume in July and August and increasing in volume again during the September sample period. Chironomid larvae, primarily Chironomus spp., was a minor food source in June increasing to major proportions during the remaining sample months.Monthly food habits comparing size groups showed -greatest utilization of zooplankton as a food source by Group 1 (20 - 49 mm) trout-perch during the sample period June; decreasing as trout-perch size increased. There was a marked decrease in zooplankton consumption in the remaining sample months for combined size groups.Monthly food habits comparing size groups showed the greatest utilization of Amphipoda during the June sample month. Size Group III (100 - 139 mm) trout-perch consumed Amphipoda in largest quantities throughout the combined study period.Monthly food habits for Insecta consumption comparing size groups were at lowest volume in June, increasing in volume during the remaining sample months. Chironomus spp. was the major food item consumed by trout-perch.Ball State UniversityMuncie, IN 47306

Yellow perch, Perca flavescens, were collected by trawling and gillnetting at 5m in a study area near Kintzele Ditch in Indiana waters of Lake Michigan. Sampling was conducted during the months of June, July and August in 1976 and 1977.Population characteristics were analyzed and compared to other studies. Growth rate and length-weight tended to be higher than in previous studies dealing with the Great Lakes, however, no specific reasons were identified. Growth differed between sexes, with females showing faster and more prolonged growth in older age fish. Significant overlap in ages I, II and III was apparent in both sexes, with growth differences evident between sexes of the same age. Virtually all (99%) age I male perch were mature, while only 15% age I females were mature. Approximately half of the age II females were mature with most age III females mature. Males were all mature at 150mm while females were all mature at 260mm.Sex ratios varied between samples, but were near unity for the combined sample period. No trends were apparent during the summer season for sex ratios in sex segregated populations.Catch-per-unit effort (CPE) remained relatively high during the entire sampling period. Lower CPE was noted with lower water temperatures. Sample variability was high throughout the sampling period, possibly due to gear selectivity, non-random distribution of individuals and repeated disturbances of the same area. When young-of-the-year were collected, their numbers were less variable than for older perch, a likely consequency of greater vulnerability to sample gear.The trawl tended to select for a wider range of sizes and greater total number of fish. The gill net consistently selected for larger fish. Neither method employed alone appeared capable of sampling the entire size range of fish.Differences in percent age in trawl and gill net samples were apparent with the gill net selecting for older fish. The trawl tended to sample a wide age range of fish.Comparison of data collected in Indiana and Michigan waters suggest fundamental differences in population structures. Indiana populations lacked significant numbers of larger, older fish which were adequately represented in samples from Michigan waters. Commercial harvest of perch in Indiana waters appears to be involved in the population structure differences.Ball State UniversityMuncie, IN 47306

Yellow perch, Perca flavescens (Mitchill), were collected by trawling and gillnetting in Indiana waters of Lake Michigan near Michigan City, Indiana. Sampling was conducted during the months of June, July and August from 1984 through 1986.Growth rates and length-weight relationships were found to be considerably lower than those reported previously. Males declined 38 mm at age I, 55 mm at age II, 56 mm at age III and 35 mm at age IV comparing 1986 to 1976. Females showed similar declines for the same period at 40 mm for age I, 58 mm at age II, 66 mm at age III and 53 mm at age IV. The primary reason for the decrease in growth appears to be due to the current high population density of yellow perch in Indiana waters of Lake Michigan.Maturation of males for 1986 appears to be slower than that of 1984. All male perch were mature by age III in 1984. However, only 68x of the males were mature at the same age in 1986. In 1984, 94% of the females were mature by age IV while 86% were mature at the same age in 1986.Differences in maturation rate may be a reflection of the reduced growth rates. Size at maturity was found to be similar for both sexes in 1984 and 1986. All females were mature by 230-239 mm in 1984 and 220-229 mm in 1986. All male perch were mature at 180-189 mm in 1984 and 220-229 mm in 1986.Total estimated average annual percent mortalities of 79, 58, 66 and 55 were calculated for combined sexes from age composition analyses end trawl catch data for 1976 and 1984-86. Yellow perch production for 100 fish was estimated for June through August using the Allen curve method. Biomass of substock ( <130 mm), stock ( >129 mm) and quality fish (200 mm or larger) were estimated using Proportional Stock Density to investigate population structure. The Allen curve biomass models were modified to more accurately reflect the trawl catch density data as an index of population changes in 1976 compared to 1984-86. Theoretical biomass for the substock component increased 23 fold from 1976 to 1986. Biomass of the stock sized fish was estimated as 15 times greater in 1986 compared to 1976. Quality fish biomass varied from year to year with the average for 1984-86 estimated as 14 times greater than 1976. The most apparent factor now influencing deterioration of growth and resultant quality of the population is decreased mortality/increased survival with increase in biomass. If the low mortality rates observed for 1984-86 remain unchanged, the data indicate continued population density increases will result in even lower growth rates, and a population dominated by a higher percentage of small, non-quality fish.Food habit analyses for 1984 were compared to a diet study of yellow perch in 1972 for the study area. Zooplankton increased from 0.4x in 1972 to 9% of the volume in 1984 for 100-175 mm perch. This trend may reflect an increase in zooplankton populations in response to the population decline of the planktivorous alewife. Young-of-the-year yellow perch made up 85% of the stomach volume for 176-225 mm perch in 1984 while none were found in samples for 1972. This clearly shows yellow perch are resorting to cannibalism resulting from excessive intraspecific competition.Diet analyses by month revealed alewife eggs were moat important during peak abundance in June and July. Yellow perch (YOY) and Pontocoreia affinis became important during August. Analysis by size interval showed zooplankton and insects (primarily Chironomidae) were important to the diet of perch in the 30-59 mm (YOY) size interval. Copepoda were important by percent volume until approximately 60 mm when the zooplankton component switched to Cladocera. Data for 60-119 mm (age I+) fish indicates alewife eggs were important during June but insects became increasingly more important during July and August. Diversity in food items consumed diminished with increase in size as diet of 120-159 mm (age II+) yellow perch consisted largely of fish. Increases in percent volume of rainbow smelt in June and July, and Y0Y perch in August for age II+ and older perch compared to younger/smaller fish may be related to increased capture success. Diet of fish larger than 160 mm (age III+ and older) consisted almost entirely of rainbow smelt and Y0Y yellow perch.Ball State UniversityMuncie, IN 47306

Predation is a strong dective force on invertebrate prey. Asellus aquaticus differs in pigmentation reed and submerged vegetation habitats in lakes. Light pigmented individuals al vegetation dominated by Chara sp. while dark pigmented individuals dominate in the reeds. These differences have been hypothesized to result from background matching. Predation pressure from fish is belived to be highest in Chara sp., while invertebrate predators are more common in the reeds. In this study I investigatedif predation from perch and damselfly larvae create different se1ection pressure on pigmentation and size of the Asellus, and if selection is affected by the structure of the habitat. The study vas carried out in aquaria in a loboratory. Regarding predation from perch a tendancy to be selective against dark pigmented individuals in Chara substrate was seen. Mortality increased with body size in Asellus, regardless of pigmentation. In the experiment mortality of Asellus decreased with body length. The results illdicate that it is not as important for Asellus to be cryptic in the reeds since it is not exposed to visual predation on the same level as in the Chara sp. where it is preferable to be small and cryptic. In the reed, large individuals are probably favorued since common predators, such as damselfly larvae, are size-limited in their prey choice.

Diss. (sammanfattning) Arkitektkopia AB, Umeå : Sveriges lantbruksuniv., 2009. / Härtill 4 uppsatser.

As a result of the legacy of industrial contamination over the last century, areas of sediment deposition in the St. Lawrence River at Cornwall, ON, contain high concentrations of mercury (Hg). The popular sport-fish species, yellow perch (Perca flavescens) and walleye (Sander vitreus) have been found to contain mercury concentrations exceeding Ontario Ministry of Environment consumption guidelines. Interestingly, a paradox exists between two contaminated sites – despite elevated sediment Hg concentrations at Zone 2, fish from Zone 1 contain higher Hg concentrations. Further research has indicated that these patterns of Hg were not attributed to growth rate, condition factor, diet composition, or trophic position of yellow perch. Rather, Hg concentrations in yellow perch may be described by the heterogeneity of prey contamination and fish bioenergetics. As a result of the paradox between total Hg (THg) concentrations in sediments and biota between two contaminated sites, it was necessary to examine the benthic invertebrate community and how it may transfer Hg from sediments to yellow perch. This apparent paradox now extends to all prey items, since prey items from the stomach contents of yellow perch caught in Zone 1 were significantly more contaminated than those of Zone 2. Use of δ15N and δ13C, measures of trophic position and energy source, respectively, indicated that prey selection, but not food chain length, may also be an important factor in explaining the variation in Hg burdens in yellow perch. Small-scale patterns of biomagnification, as shown by a comparison of δ15N and logTHg, indicated that the rates of biomagnification were similar among zones, but the amount of THg present at the base of the food web was twice as high at Zone 1 as at other contaminated sites. Overall, the relative importance of vertical and horizontal food web structure changed spatially and temporally, highly influencing THg concentrations of prey items and yellow perch. / Thesis (Master, Biology) -- Queen's University, 2007-08-02 08:02:40.26

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