Dissertations / Theses: 'Fish populations'

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Durrant, Christopher. "Effects of metal contamination on fish populations." Thesis, King's College London (University of London), 2010. http://kclpure.kcl.ac.uk/portal/en/theses/effects-of-metal-contamination-on-fish-populations(cd690b4f-265d-48cd-805e-c561e411b370).html.

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Nicol, Elizabeth. "Long-term effects of oestrogenic effluent exposure on wild fish populations." Thesis, Brunel University, 2014. http://bura.brunel.ac.uk/handle/2438/10826.

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Freshwater streams in the developed world are becoming increasingly dominated by treated wastewater. Continually discharged into most surface waters, these effluents contain a suite of bioactive man-made chemicals, including steroid and non-steroid oestrogens, which have been found to feminise male fish, skew sex ratios, and cause reproductive failure. However, the consequences of reproductive disruption remain poorly explored at the population level. This thesis was initiated to evaluate how oestrogenic contaminants might influence the population ecology of a common cyprinid, the roach (Rutilus rutilus). An investigation encompassing population structure, multigenerational exposure and the role of additional drivers of fish population dynamics was undertaken to contextualise the effects of oestrogenic effluents on wild fish populations. Population genetic analysis of UK roach found they exhibit moderately high levels of genetic diversity and significant intra-river genetic structure. Genetically differentiated local subpopulations indicate little interbreeding and limited gene flow, consistent with a typical metapopulation that has not been homogenised by restocking. Similarly, my thesis demonstrates no significant relationship between effluent exposure and Ne (effective population size) or genetic diversity of roach populations, albeit a 65% reduction in Ne is possible at highly polluted sites. River stretches contaminated with high levels of effluent can support breeding populations, which recruit successfully with minimal immigration from less contaminated sites. Multigenerational effects of effluent exposure on roach were also evaluated experimentally using reproductive success from breeding adults over three generations. Lifelong exposure to 100% treated effluent resulted in feminised phenotypes (ovarian cavities and intersex condition) in males but no observable effect on females. Additionally, despite gonadal disruption in males and effluent exposure of their mothers, I found no detrimental effect on their ability to compete with control fish. Instead, reproductive success was primarily determined by body size. A novel approach considering additional fish population drivers suggests that genetic diversity and species diversity decline in parallel with an increasing presence of disturbed land, when combined with geographical isolation. In conclusion, group assemblage and genetic structure of fish populations appears multi-causal and cannot be disaggregated, such that a single environmental characteristic can be shown to drive patterns of population success.

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Taylor, Ryan James. "Applications of fish scale analysis to understand growth dynamics of fish populations." Thesis, University of Hull, 2012. http://hydra.hull.ac.uk/resources/hull:5771.

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The use of hard structures to derive ecological information about fish populations is a fundamental tool in fisheries assessment, specifically the back-calculation of fish lengths. This study highlights the potential errors associated with correction factors (c) because of poor sampling and provides a validation of (c) values. In addition, classical fisheries assumptions about the relationship between scale radius and fish body length were tested. As a result, variability or error of correction factors can be reduced by having a minimum of 30 samples with at least 4 age classes represented. Alternatively the (c) provided can be used as a standard (c) factor for each species, eliminating the variance caused by poor sampling. Finally, the development of standard intercept values (based on observation of juvenile fish) should be promoted to replace or validate mathematically derived (c). The ability to accurately determine the age and growth of fish is an important tool in fishery biology and therefore it is fundamental to this work that all steps should be taken to increase the accuracy of back-calculated length-at-age data and account for size when fish lay down scales. To account for potential error associated with a correction factor, larval fish were routinely sampled to identify patterns of squamation, providing preliminary reference data for correction factors used in back-calculation of fish length-at-age. Determination of the length at squamation for more specimens will allow for the derivation of standard correction factors for each species that can be used across the species’ distribution. Geometric morphometric (GM) analysis of fish scales has been shown to be a good discriminator of genera using a fixed landmark approach. However, freshwater fish scales are often irregular in shape; therefore it is not possible to identify identical locations on all individuals. This study provides evidence that scale morphology can be used to discriminate riverine fish species. The analysis of fish scale morphology is inexpensive, quick, non-destructive, and informative and could easily be added to existing monitoring programmes. This study highlights the potentially important and opportunistic information that can be gained from the GM analysis of fish scales. It is therefore anticipated that this study will be fundamental in shaping future fish population assessments. It is recognised amongst scientists that fish growth rates vary across a catchment, with species typically achieving greater growth rates in their ‘preferred’ habitats. Similarly, previous authors have identified that growth variation exists for different species and populations. This study has found that the geographic location of a river/region influences the growth rates of freshwater fishes commonly found in England. The method of constructing regional growth curves and subsequent statistical analysis discussed in this study should be adopted by fisheries scientists, because current national growth rates may be unachievable in specific regions. Furthermore, current national curves are inappropriate for growth and population analysis because they may be biased by an individual river and/or region. This study is one of the few studies to examine the differences between regional recruitment success, and found similarities and differences at both the regional and national level. With recruitment success a key requirement of monitoring fish populations under the WFD, it is hoped the information provided here will aid fisheries scientists to understand the factors affecting regional and national recruitment success. Studies on the impact of climate change on fish populations have typically focused on suggesting, rather than predicting, the effects on lentic species rather than lotic species. Furthermore, these studies often deal with American rather than European ecosystems. To address this, predicted changes in the climate of the UK were used to model likely influences on fish populations, expressed as the length of young of year (YOY) fish achieved by the end of the first growth period (May-September), juvenile and adult growth (annual growth increment, AGI) and recruitment success (year class strength, YCS), for three cyprinid fish. This study found that climate change is likely to increase the propensity for cyprinid fish to thrive, although the exact mechanism will depend on inter-annual variability in temperature rises and the timing of flow events. Notwithstanding the limitations of this study, it provides ecologists with a greater understanding of climate change and its potential impact on European, lotic fish populations.

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Sapp, Shawn A. "Population trends of major near-shore fish species in Indiana waters of Lake Michigan." Virtual Press, 1999. http://liblink.bsu.edu/uhtbin/catkey/1125023.

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The purpose of this research was to determine population trends of major nearshore fish species in Indiana waters of Lake Michigan from 1984 to 1998 to gain insight into species dynamics. Index trawl samples were collected twice monthly from June through August at three locations. Trends of catch-per-unit-effort (CPUE) were investigated for the most abundant species: yellow perch (Perca flavescens), alewife (Alosa pseudoharengus), spottail shiner (Notropis hudsonius), rainbow smelt (Osmerus mord iz), and bloater (Coregonus hoyi). Trawl catch of yellow perch, alewife, and spottail shiners at sites M, K, and G were strongly correlated suggesting similar fluctuations. Young-of-the-year trawl catch revealed that insight to population dynamics of species was not always reliable. Trawl CPUE of > age 1 fish provided insight to dynamics of the major species at all sample locations with strong trend similarities between sites. No strong major species interactions were found using simple linear correlations.
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Lebepe, Jeffrey. "Assessment of the effects of environmental contaminants on feral fish populations in the Olifants river system." Thesis, University of Limpopo, 2018. http://hdl.handle.net/10386/2450.

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Thesis (Ph.D (Zoology)) --University of Limpopo, 2018
Freshwater ecosystems are the most threatened systems globally, suffering from channel modification, over extraction of water and, of particular concern, pollution. In South Africa, Olifants River is categorised as the third most polluted river system. Acid mine drainage seeping from derelict and abandoned mines has been described as the primary stressor in the upper Olifants catchment. The increase of metal concentration in the water, sediment and fish tissues has been evident over the past few decades. As a result, there has been an increasing concern regarding the effects of increased metal concentrations on the health of fish and the safety of communities consuming fish from the polluted Olifants River system. This study used enzymatic and histopathologic biomarkers to assess the physiological response of Oreochromis mossambicus and Labeo rosae to environmental contaminants. The study further investigated the metal accumulation trend of across different fish tissues and assessed the edibility of O. mossambicus and L. rosae from Loskop and Flag Boshielo dams. Water, sediment and fish samplings were carried out concurrently during low flow and high flow seasons in 2014. Water and sediment sampling were done at the inflow, middle and dam wall. A minimum of 10 fish specimens for each species were collected from Loskop and Flag Boshielo dams during each sampling. For bioaccumulation analysis, liver, gill and muscle tissues were dissected out, wrapped with aluminium foil and frozen. Frozen samples were sent to SANAS accredited laboratory for metal analysis. For Histopathology, tissues were fixed in 10% neutral buffered formalin prior processing. Tissue processing was done at the Pathology laboratory of the University of Pretoria, Onderstepoort campus. For biomarker analysis, liver and brain tissues were fixed in liquid nitrogen in the field and transferred to the -80°C biofreezer at the University of Limpopo, Biotechnology Unit laboratory. Metal concentrations in the muscle tissue were used to calculate hazard quotient for human health risk assessment which was based on the assumptions that an adult weighting 70 kg consume 150 g portion once per week. Alkaline pH was observed in the water throughout the study. Most water constituents were within the guidelines at both dams. The water at Flag Boshielo Dam was oligotrophic with Loskop Dam showing mesotrophic conditions. Concentrations were below detection level for most metals; however, significant concentrations were recorded in the bottom sediment. Although Loskop Dam is being described as a repository for pollutants from the upper Olifants catchment, no significant differences (p>0.05) were observed for metal concentrations in sediment between the two dams. Coinciding with sediment metal concentrations, liver, gills and muscle have shown notable concentrations for both species at Loskop and Flag Boshielo dams. The common trend of liver accumulating higher metal concentration followed by gill and muscle (liver>gills>muscle) was observed for most metals on O. mossambicus and L. rosae at both dams. In contrast, lead, strontium and manganese showed higher concentrations in the gills. Muscle exhibited lowest concentrations for most metals. Remarkable trends on the activities of biomarkers, lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G6PDH), glutathione-S-transferase (GST) and acetylcholinesterase (AChE) were detected for both species at Loskop and Flag Boshielo dams. Labeo rosae population have shown a significantly high (p<0.05) LDH activities at Loskop Dam and no significant difference (p>0.05) was observed for Oreochromis mossambicus. Glucose-6-phosphate dehydrogenase activities exhibited no significant difference (p>0.05) for both species between the two dams. Labeo rosae have shown a significantly high (p<0.05) GST activities at Loskop Dam whereas Oreochromis mossambicus exhibited no significant difference (p>0.05) between the two dams. Acetylcholinesterase (AChE) has shown no significant difference (p>0.05) for both species between the Loskop and Flag Boshielo dams. LDH, G6PDH and GST activities have shown relationship with metal concentrations, which makes them good biomarkers of metal exposure.The condition factor indicated that overall conditions of O. mossambicus and L. rosae from Loskop and Flag Boshielo dams were good. Hepatosomatic index results were not conclusive. Most histopathological alterations were recorded on both species at both dams, but with different magnitude of severity. Regressive changes were more prominent in the liver and gills of both species at Loskop and Flag Boshielo dams followed by progressive change. Gills of Oreochromis mossambicus exhibited moderate modifications (score >20) at Loskop Dam and slight modification (score <20) at Flag Boshielo Dam. Labeo rosae populations have shown slight modifications (score <20) in the gills at both dams. Both species have shown significant difference (p<0.05) on the gill index between the two dams. Liver index has also exhibited significant difference (p<0.05) for each species between Loskop and Flag Boshielo dams. Slight modifications (score <20) were observed in the liver for both species at Loskop and Flag Boshielo dams. Both species have shown to accumulate metals within their tissues with liver accumulating higher concentration for most metals, followed by gills and muscle, respectively. Although muscle showed to accumulate lesser metal concentrations, it still raise a serious concern as it is the tissue consumed by human. Lead, chromium, cobalt and antimony concentrations have been the only metals of concern in this river system over the past few years; nevertheless, the present study has shown that other metals viz. arsenic, silver and selenium have exceeded international levels for safe consumption. Given the metal concentration trend reported over the past two decade in fish tissues, there is a need for urgent intervention to address the acid mine drainage problem to ensure sustainable development of the Olifants River and safety of communities depending on it for their livelihood.
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Franckowiak, Ryan Patrick. "Temporal dynamics of genetic variation within the Escanaba Lake walleye population : implications for managing the genetic resources of naturally recruiting walleye populations /." Link to Full-text, 2005. http://epapers.uwsp.edu/thesis/2006/Franckowiak.pdf.

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Dux, Andrew Martin. "Distribution and population characteristics of lake trout in Lake McDonald, Glacier National Park implications for suppression /." Thesis, Connect to this title online, 2005. http://etd.lib.montana.edu/etd/2005/dux/DuxA1205.pdf.

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Thesis (M.S.)--Montana State University--Bozeman, 2005.
Title from PDF t.p. (viewed on Mar. 30, 2008). Chairperson, Graduate Committee: Christopher S. Guy. Includes bibliographical references (p. 67-76).

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White, William T. "Aspects of the biology of elasmobranchs in a subtropical embayment in Western Australia and of chondrichthyan fisheries in Indonesia /." Access via Murdoch University Digital Theses Project, 2003. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040510.154948.

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Markovsky, W. Coult. "The role of the Cape Fear River discharge plume in fisheries production : aggregation and trophic enhancement /." Electronic version (Microsoft Word), 2004. http://dl.uncw.edu/etd/2004/markovskyw/wcoultmarkovsky.doc.

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Mohamed, A. R. M. "A study of fish populations in Abberton Reservoir." Thesis, University of Essex, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374718.

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Panikian, Garabet. "Statistical modelling of marine fish populations and communities." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/17063/.

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Sustainable fisheries management require an understanding of the relationship between the adult population and the number of juveniles successfully added to that population each year. The process driving larval survival to enter a given stage of a fish population is highly variable and this pattern of variability reflects the strength of density-dependent mortality. Marine ecosystems are generally threatened by climate change and overfishing; the coupling of these two sources have encouraged scientists to develop end-to-end ecosystem models to study the interactions of organisms at different trophic levels and to understand their behaviours in response to climate change. Our understanding of this important and massively complex system has been constrained historically by the limited amount of data available. Recent technological advances are beginning to address this lack of data, but there is an urgent need for careful statistical methodology to synthesise this information and to make reliable predictions based upon it. In this thesis I developed methodologies specifically designed to interpret the patterns of variability in recruitment by accurately estimating the degree of heteroscedasticity in 90 published stock-recruitment datasets. To better estimate the accuracy of model parameters, I employed a Bayesian hierarchical modelling framework and applied this to multiple sets of fish populations with different model structures. Finally, I developed an end-to-end ecological model that takes into account biotic and abiotic factors, together with data on the fish communities, to assess the organisation of the marine ecosystem and to investigate the potential effects of weather or climate changes. The work developed within this thesis highlights the importance of statistical methods in estimating the patterns of variability and community structure in fish populations as well as describing the way organisms and environmental factors interact within an ecosystem.

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Burrow, Jennifer. "Mechanistic models of recruitment variability in fish populations." Thesis, University of York, 2011. http://etheses.whiterose.ac.uk/1611/.

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There are serious concerns worldwide about the decline of exploited fish stocks. The number of fish larvae surviving to be recruited into the adult population each year is fundamental to the long-term stability of a fish stock. Monitoring and predicting recruitment is a crucial component of managing economically important fisheries worldwide. Fish recruitment can vary by an order of magnitude, or more, between years, and the larval stage is a key determining factor. Fish larvae are born into an extremely variable environment, with high mortality rates, and so it is not surprising that the number surviving to join the adult population is highly variable. This thesis presents simple stochastic, mechanistic larval growth models, developed and utilised to investigate recruitment probabilities and variability. The models are mechanistic in that they are based on consideration of the key ecological processes at work, and not on statistical regression analyses or similar techniques. At the heart of the thesis lies a stochastic drift-diffusion model for the growth of an individual larva. Further mathematical and ecological complexity is built up through consideration of both the temporal and spatial heterogeneity of larval food sources, primarily zooplankton. Results illustrate the impact of stochasticity in the timing of peak food abundance, and the patchiness of the prey, on recruitment variability. The idea of non-constant variance in recruitment is also investigated, with the aim of testing its practical relevance to fisheries management. It is demonstrated that the currently available stock-recruitment time series are at least one order of magnitude too short to reliably fit such models. Management implications are illustrated using simple models and published recruitment data for two exploited stocks. The work developed within this thesis highlights the importance of stochasticity in fish larval growth and recruitment, and the power of simple mechanistic models in examining these ideas.

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Schueller, Amy M. "Modeling the sustainability of walleye populations in northern Wisconsin lakes /." Link to abstract, 2005. http://epapers.uwsp.edu/abstracts/2005/Schueller.pdf.

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Bellgraph, Brian Joseph. "Competition potential between sauger and walleye in non-native sympatry historical trends and resource overlap in the middle Missouri River, Montana /." Thesis, Montana State University, 2006. http://etd.lib.montana.edu/etd/2006/bellgraph/BellgraphB0506.pdf.

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Thesis (M.S.)--Montana State University--Bozeman, 2006.
Title from PDF t.p. (viewed on Mar. 30, 2008). Chairperson, Graduate Committee: Christopher S. Guy. Includes bibliographical references (p. 65-72).

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Weeks, Jordan. "Walleye and muskellunge movement in the Manitowish Chain of Lakes, Vilas County, Wisconsin /." Link to full-text, 2006. http://epapers.uwsp.edu/thesis/2006/weeks.pdf.

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Ernst, Billy. "An investigation on length-based models used in quantitative population modeling /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/5281.

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Hancock, Andrew. "The biology and fishery of Roe's abalone Haliotis roei Gray in south-western Australia, with emphasis on the Perth fishery /." Connect to this title, 2004. http://theses.library.uwa.edu.au/adt-WU2004.0068.

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Haughey, Joanne Lee. "Culverts as potential barriers to fish movement." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 65 p, 2007. http://proquest.umi.com/pqdweb?did=1251899181&sid=1&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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Milligan, Rosanna J. "Natural and anthropogenic drivers of deep-sea fish populations." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/5981/.

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Deep-sea demersal fish are likely to be highly important in structuring deep-sea ecosystems, but a paucity of data means that relatively little is known about the spatial and temporal processes that influence their distributions or how these may change at different scales of observation. As human activities continue to expand into deeper waters, the importance of understanding these processes is becoming increasingly urgent. The oil and gas industry are expanding into deeper waters as coastal oil reserves diminish, but potential long-term effects on the benthos are unknown. Time-lapse photographic data collected from within an active oil field on the Angolan continental slope (tropical eastern Atlantic) detected no significant differences in the community composition of fish compared to a reference site. Significant seasonal changes in the total abundance of demersal fish were detected however, with >20-fold increases in abundance recorded from the oil-field observatory. These results suggest that the deep-sea environment in this region is likely to be highly dynamic over seasonal and decadal timescales, and some possible drivers are discussed. Understanding the spatial distributions of fish is important in understanding their potential ecological roles within an ecosystem and how they may benefit from spatially-explicit management measures. In the bathyal NE Atlantic, the demersal fish communities associated with cold-water corals (CWC) appeared to be influenced by processes operating at multiple spatial scales. At the broadest scales (100s km), depth was a significant predictor of community composition, while habitat type was significant at the finest scales (m). These results highlight the need to account for the effects of scale in observational research and may explain why no consensus has thus far been reached regarding the role of CWC habitats for deep-water fish in the NE Atlantic and provide a possible framework for approaching future deep-water community studies. In abyssal depths, the importance of habitat heterogeneity in structuring fish communities has never been previously studied. Investigations of the spatial distributions of demersal abyssal fish around a small (c. 250 m high) abyssal hill showed that the distribution pattern of the total fish fauna and the two dominant taxa were not significantly different from random. Random distributions are unusual in nature and these results suggest that the environment may be essentially homogeneous to abyssal fish at spatial scales between 100 m – 10 km and suggests no influence of the abyssal hill on the fish fauna. The results highlight the great potential value of autonomous vehicles in extending abyssal research over broader spatial scales. Experimental studies investigating the effects of large-scale ecological processes on deep-water ecosystems are often unfeasible. Mathematical models can provide an alternative methodology, but have not been widely applied to the deep sea. In Chapter 5, a simple mathematical model was developed to explore the effects of large, transient resource pulses on the population dynamics of the abyssal holothurian Amperima rosea. Large, apparently transient increases in the biomass of this species have been observed at the Porcupine Abyssal Plain during two “Amperima events”, but the mechanisms leading to the increases remain unclear. The simulations showed that Amperima biomasses within the observed range of the smaller “Amperima event” could be simulated in some circumstances following the addition of a single, large resource pulse (10000 – 20000 g POC ha-1) to the model, which led to a short-term, transient increase in Amperima biomass before a return to previous levels. None of the simulations produced unstable population dynamics. While the scarcity of empirical data from the PAP means that these results must be treated cautiously, they highlight the potential for temporal changes in food supply to rapidly alter the dynamics of abyssal populations.

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Boisclair, Daniel. "Among-population variability in fish growth rates : the influence of food consumption, prey type and fish community." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75957.

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I assessed the relationship between growth of fish in situ, food consumption, prey type and fish community descriptors in 12 perch (Perca flavescens) populations exhibiting a 1.8 to 10-fold range in growth rates.
Perch growth rates consistently decreased as fish numerical density increased (r$ sp2$ = 0.60) and increased as feeding levels increased (r$ sp2$ = 0.30). I found no significant relationship between the quantity of food consumed by perch and fish numerical density. Prey quality explained from 50 to 95% of the observed variability in growth but was related to fish numerical density in only one of the 3 perch age classes studied.
I conclude that non-exploitative interactions (operating through increased activity costs) is a more viable explanation for the among-population variability in fish growth rates than is exploitative competition (yielding decreases in the total quantities of food consumed and/or prey quality).

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Carden, Kerilynn M. "Macrophytes as fish habitat : the role of macrophyte morphology and bed complexity in fish species distributions /." Link to abstract, 2002. http://epapers.uwsp.edu/abstracts/2002/Carden.pdf.

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Locascio, James Vincent. "Passive Acoustic Studies of Estuarine Fish Populations of Southwest Florida." Scholar Commons, 2010. https://scholarcommons.usf.edu/etd/1700.

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Recordings of fish sound production were made in Charlotte Harbor, Florida using Long Term Acoustic Recording Systems (LARS) programmed to record 10 seconds of sound every 10 minutes. Results demonstrated a strong circadian pattern in fish sound production that occurred within a few hours of dusk each evening. Sound production lasted on average 8.7 hrs each evening during the peak spawning season. LARS were deployed when Hurricane Charley crossed Charlotte Harbor in August, 2004. The hurricane did not inhibit nightly chorusing events of spawning fish. Rather, sound levels produced by spawning fish on the night of and 3 days after the hurricane were higher and lasted longer than any of the 9 days recorded prior to the hurricane. Acoustic time series data recorded at multiple sites in Charlotte Harbor during 2005 revealed changes in the spatial distribution of fish sound production in response to increased freshwater inflow and consequent decreased bottom dissolved oxygen concentrations in early June. Fish sound production decreased rapidly over several days at study sites in the northern portion of the harbor most immediately affected by changes in environmental conditions. Meanwhile, fish sound production increased at the study site furthest seaward where normoxic levels were sustained. By August levels of fresh water inflow decreased substantially, bottom dissolved oxygen levels increased and sound production resumed at sites previously affected by these conditions. Fish sound production began intermittently in February and ended in November. Peak levels were reached by mid-late April / early May and continued throughout the summer time. Seasonal patterns of sound production match the reported spawning periods of estuarine sciaenid species recorded. Black drum sound production was measured in the canal systems of Cape Coral and Punta Gorda, Florida during the 2004-2006 spawning seasons. The circadian pattern of sound production was similar to other sciaenids documented in Charlotte Harbor. Seasonal patterns of black drum sound production occurred during October through April and peaked in February. This seasonal period of sound production also matched patterns of black drum reproductive readiness and spawning reported in the literature for the Gulf of Mexico. A hydrophone array was used in the Cape Coral canal system to localize calling black drum and measure source levels and propagation of calls. Source level estimates averaged 165 dBRMS re: 1muPa SPL (SD=1.0) (n = 1,025). Call energy was concentrated in the fundamental frequency (94 Hz) and first two harmonics (188 Hz and 282 Hz). A square root model best described propagation of the fundamental frequency and first harmonic and a log 10 model best described the second harmonic. Based on the mean RMS source level, signal propagation, background levels, and hearing sensitivity, the communication range of black drum at the study site was estimated at between 33 and 108 meters and was limited by background levels, not auditory sensitivity. The timing and levels of sound production and egg production were compared in black drum. Eggs were collected hourly from 1800 - 0400 by surface plankton tows on two consecutive evenings while black drum sound production was continuously recorded. This sampling effort was conducted five separate times from January through April, 2006. Evidence of the time of spawning was indicated by the collection of blastodiscs (fertilized single cell eggs) or back calculated early cleavage stage eggs. Neither the timing nor the quantity of sound production was positively correlated with egg production on a nightly basis and the greatest densities of eggs were collected on evenings which had the lowest levels of sound production. This may have been due to differences in the fecundity of individual females spawning on the evenings when sampling was conducted.

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Spencer, Erin Elizabeth. "Factors Controlling Alewife (Alosa psuedoharengus) Population Abundance among Four Rivers in Mid-Coast Maine." Fogler Library, University of Maine, 2009. http://www.library.umaine.edu/theses/pdf/SpencerEE2009.pdf.

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Xu, Yi. "Modeling the Seasonal and Interannual Variability of Peruvian Anchovy (Engraulis ringens) Population Dynamics: Linking Environmental Conditions with Fish." Fogler Library, University of Maine, 2009. http://www.library.umaine.edu/theses/pdf/XuY2009.pdf.

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Abrahamse, Matthew S. "Abundance and structure of burbot Lota lota populations in lakes and reservoirs of the Wind River drainage, Wyoming." Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1797714301&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.

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Hosack, Michael A. "Population dynamics of lake whitefish in Lake Pend Oreille, Idaho /." Link to full text, 2007. http://epapers.uwsp.edu/thesis/2007/Hosack.pdf.

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Thesis (M.S.)--University of Wisconsin--Stevens Point, 2007.
Submitted in partial fulfillment of the requirements for the degree Master of Science in Natural Resources (Fisheries), College of Natural Resources. Includes bibliographical references (leaves 156-174).

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Bridson, Jessica. "The effect of fishing on the evolution of North Sea Cod." Thesis, University of Strathclyde, 2001. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=9352.

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Zipfel, Katherine J. "The distribution and status of native walleye (Sander vitreus) stocks in West Virginia." Ohio : Ohio University, 2006. http://www.ohiolink.edu/etd/view.cgi?ohiou1164229538.

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Jacklin, Timothy. "Aspects of fishery management on the River Trent : a large, lowland river." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324124.

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Kitterman, Christy L. "An assessment of barotrauma and the stock characteristics of Tennessee River sauger populations a thesis presented to the faculty of the Graduate School, Tennessee Technological University /." Click to access online, 2009. http://proquest.umi.com/pqdweb?index=4&did=1908035871&SrchMode=1&sid=1&Fmt=6&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1265309878&clientId=28564.

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Deroba, Jonathan J. "Evaluating methods of estimating walleye angling exploitation in northern Wisconsin lakes /." Link to abstracts, 2004. http://epapers.uwsp.edu/abstracts/2004/Deroba.pdf.

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Linton, Brian C. "Population dynamics of a recovering lake trout population in Wisconsin waters of Lake Superior, 1980-2001 /." View abstract (PDF format), 2002. http://epapers.uwsp.edu/abstracts/2002/linton.pdf.

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Scoulding, Ben. "In situ target strength of pelagic fish." Thesis, University of Aberdeen, 2016. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=230706.

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Longval, Brooke A. "Biomass spectra in Narragansett Bay from phytoplankton to fish /." View online ; access limited to URI, 2009. http://digitalcommons.uri.edu/dissertations/AAI3401124.

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Gibbons, Wade N. "Suitability of small fish species for monitoring the effects of pulp mill effluent on fish populations." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq21350.pdf.

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Hense, Zina. "Stream fish populations in a watershed scale context for fish community dynamics in central Appalachian watersheds." Morgantown, W. Va. : [West Virginia University Libraries], 2007. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5259.

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Thesis (M.S.)--West Virginia University, 2007.
Title from document title page. Document formatted into pages; contains vi, 97 p. : ill., maps. Includes abstract. Includes bibliographical references.

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Calles, Olle. "Re-establishment of connectivity for fish populations in regulated rivers." Doctoral thesis, Karlstad University, Faculty of Social and Life Sciences, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-1400.

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The hydropower industry has altered connectivity in many rivers during the last century. Many fish species depend on both an intact longitudinal connectivity to be able to migrate between spawning, feeding and winter habitats, and vertical connectivity for development and survival of incubating embryos and larvae in the gravel. The objective of this thesis was to examine problems and remedial measures associated with disrupted longitudinal and vertical connectivity in regulated rivers. The issue of longitudinal connectivity was studied in the River Emån by evaluating the efficiency of two nature-like fishways for anadromous brown trout. Telemetry studies showed that the combined efficiency for the two fishways in 2001-2004 was 60.5%. The passage efficiencies of both fishways were high for trout (89-100%), but also for other species such as chub, perch, tench, burbot and roach (74%). The attraction efficiencies were largely dependent on power plant operation, and generally high for the fishway situated next to the tail-race and low for the fishway situated inside the former channel. More than half of the trout spawners were also observed using the fishways for downstream passage. The densities of brown trout yearlings upstream of the fishways were higher after the fishways were built than during pre-fishway years. Smolts produced upstream of the fishways were observed migrating downstream in 2003-2005. The percentage of smolts that passed both power plants in was 51%, with losses being attributed to predation (15%), turbine-induced mortality (16%) and other reasons (18%). Turbine-induced mortality was higher (40%) at the power plant with four small Francis runners, than at the power plant with one large Kaplan runner (12%). The issue of vertical connectivity was studied in three rivers in Värmland, one unregulated, and two regulated, one of which had no minimum flow requirements. In the unregulated river, temporal patterns in hyporheic water chemistry correlated to variation in surface water chemistry and discharge as expected. In the regulated rivers, the hyporheic water chemistry showed little correlation to discharge or surface water chemistry. The intra-gravel water chemistry conditions for brown trout eggs were more favourable in the unregulated river, characterised by high oxygen levels, than in the two regulated rivers. The regulated river with no minimum flow requirements had critically low oxygen levels at the end of the incubation period.

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Svanbäck, Richard. "Ecology and Evolution of Adaptive Morphological Variation in Fish Populations." Doctoral thesis, Umeå University, Ecology and Environmental Science, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-196.

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The work in this thesis deals with the ecology and evolution of adaptive individual variation. Ecologists have long used niche theory to describe the ecology of a species as a whole, treating conspecific individuals as ecological equivalent. During recent years, research about individual variation in diet and morphology has gained interest in adaptive radiations and ecological speciation. Such variation among individual niche use may have important conservation implications as well as ecological and evolutionary implications. However, up to date we know very little about the extension of this phenomenon in natural populations and the mechanisms behind it.

The results in this thesis show that the extension of individual diet specialization is widely spread throughout the animal kingdom. The variation in diet is mainly correlated to morphological variation but not always. Furthermore, this variation in diet and morphology among individuals could be both genetically determined and environmentally induced and it mainly comes from trade-offs in foraging efficiency between different prey types.

The results from a number of studies of perch also show that individual perch differ in morphology and diet depending on habitat, where littoral perch has a deeper body compared to pelagic perch. This difference in morphology corresponds to functional expectations and is related to foraging efficiency trade-offs between foraging in the littoral and pelagic zone of a lake. The variation in morphology in perch is mainly due to phenotypic plasticity but there are also small genetic differences between the littoral and pelagic perch. Two separate studies show that both predation and competition may be important mechanism for the variation in morphology and diet in perch.

In conclusion, the results in this thesis show that individual variation in diet and habitat choice is a common phenomenon with lots of ecological and evolutionary implications. However, there are many mechanisms involved in this phenomenon on which we are just about to start learning more about, and only further research in this area will give us the full insight.

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Engström, Henri. "Effects of Great Cormorant Predation on Fish Populations and Fishery." Doctoral thesis, Uppsala University, Department of Evolutionary Biology, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1506.

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The strong increase in number of Great cormorants Phalacrocorax carbo in Sweden in recent years has led to conflicts - particularly with fishery. This thesis focuses on the possible effects of cormorant predation on fish populations. In total, data from 15 lakes in South Sweden were included in this study while most studies were carried out in Lake Ymsen. The results suggest that the impact of cormorant predation on natural fish populations was small, and I observed no decline in fish mass after cormorants established. Cormorant predation on eel was difficult to evaluate because of several confounding factors.

Ruffe, roach and perch were the most important prey species to the cormorants and most fish taken were small. Cormorants do not seem to catch species and sizes in proportion to their occurrence in the fish community.

Total fish removal by cormorants varied considerably among lakes (0.2-15.0 kg/ha) and cormorant population sizes at the different lakes were significantly positively correlated with fishery catches, which in turn was significantly positively correlated with total phosphorous levels. Thus, cormorant densities in lakes, and perhaps elsewhere, seem to be governed chiefly by fish densities. The fact that cormorant predation appears not to reduce fish densities suggest cormorants to be regulated by other means than prey depletion. The mechanism behind population regulation could be a behavioural response of fish, making fish more difficult to catch for the cormorants.

In recent years, cormorant populations have been subjected to intensive legal and illegal actions with the aim to reduce cormorant numbers. However, the actions currently carried are well below the efforts needed to limit population sizes. To conclude, cormorants appear to compete little with fishery, with regards to free-living fish. The main problem is that cormorants sometimes damage and take away fish in fishing gears.

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Svanbäck, Richard. "Ecology and evolution of adaptive morphological variation in fish populations /." Umeå : Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-196.

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Engström, Henri. "Effects of great cormorant predation on fish populations and fishery /." Uppsala : Acta Universitatis Upsaliensis : Univ-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-5164-0/.

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42

Hedström, Per. "Climate change impacts on production and dynamics of fish populations." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-128007.

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Ongoing climate change is predicted to increase water temperatures and export of terrestrial dissolved matter (TDOM) to aquatic ecosystems influencing ecosystem productivity, food web dynamics and production of top consumers. Ecosystem productivity is mainly determined by the rates of primary production (GPP) in turn controlled by nutrients, light availability and temperature, while temperature alone affect vital rates like consumption and metabolic rates and maintenance requirements of consumers. Increased level of TDOM causes brownification of water which may cause light limitation in algae and decrease GPP and especially so in the benthic habitat. Temperature increase has a been suggested to increase metabolic rates of consumers to larger extent than the corresponding effect on GPP, which suggest reduced top consumer biomass and production with warming. The aim of this thesis was to experimentally study the effects of increased temperature and TDOM on habitat specific and whole ecosystem GPP and fish densities and production. In a replicated large-scale pond experiment encompassing natural food webs of lotic ecosystems I studied population level responses to warming and brownification in the three- spined stickleback (Gasterosteus aculeatus). Results showed overall that warming had no effect on whole ecosystem GPP, likely due to nutrient limitation, while TDOM input decreased benthic GPP but stimulated pelagic GPP. In fish, results first of all suggested that recruitment in sticklebacks over summer was negatively affected by warming as maintenance requirements in relation to GPP increased and thereby increased starvation mortality of young-of-the-year (YOY) sticklebacks. Secondly, brownification increased mortality over winter in YOY as the negative effect on light conditions likely decreased search efficiency and caused lower consumption rates and starvation over winter in sticklebacks. Third, seasonal production of YOY, older, and total stickleback production was negatively affected by warming, while increased TDOM caused decreased YOY and total fish production. The combined effect of the two was intermediate but still negative. Temperature effects on fish production were likely a result of increased energy requirements of fish in relation to resource production and intake rates whereas the negative effect of TDOM likely was a result of decreased benthic resource production. Finally, effects of warming over a three-year period caused total fish density and biomass and abundance of both mature and old fish to decrease, while proportion of young fish increased. The main cause behind the strong negative effects of warming on fish population biomass and changes in population demographic parameters were likely the temperature driven increased energy requirements relative to resource production and cohort competition. The results from this thesis suggest that predicted climate change impacts on lentic aquatic ecosystems will decrease future densities and biomass of fish and negatively affect fish production and especially so in systems dominated by benthic resource production.

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Frey, Aaron Paul. "Trophic interactions between walleye and smallmouth bass in a north temperate lake /." Link to Abstract, 2003. http://epapers.uwsp.edu/abstracts/2003/frey.pdf.

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Errigo, Michael. "Structured Errors in Modeling Fishery Population Dynamics and in Stock Assessment." Fogler Library, University of Maine, 2008. http://www.library.umaine.edu/theses/pdf/ErrigoM2008.pdf.

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Bacher, Kathrin. "Interactions between fish farming, wild fish populations, local fisheries and society: a case study in Catalonia, Spain." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/284844.

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The overarching goal of this doctoral thesis was to advance the understanding of the interactions between marine fish farming, wild fish populations, the local small-scale fishery and the society. This thesis was designed as a multi-disciplinary study and is divided into three different sections: ecology (chapter 1 and 2), fisheries (chapter 3) and social science (chapter 4). In the ecological part we examined the spatial and temporal extent of the attraction effect of wild fish at an Atlantic bluefin tuna and a Gilthead seabream farm. At both farms wild fish aggregated closely to the cage structure, revealing an abrupt decline of fish abundance rather than a gradient. The intensity of the cage effect varied according to farm, season and depth. At the seabream farm, the cage effect persisted year round, whereas at the tuna farm, the effect was restricted to summer and spring. The variability of wild fish aggregations within the Gilthead seabream farm was analyzed because it can be a distorting factor in estimating the farm attraction effect. Our findings showed that at the surface, fish abundance was significantly higher during feeding compared with non-feeding periods. Moreover, the distance from the feeding vessel significantly influenced fish aggregations in the water column. At the bottom, substrate type was the dominant factor explaining aggregation variability. The effect of fish farming on the small-scale fishery was evaluated in order to determine whether farms act as protection zones or as traps for wild fish populations. The findings revealed a relevant amount of commercial and recreational fishing effort in farm vicinity. However, the results showed no benefit or difference of fishing in close proximity to the farm compared to areas away from the farm (in terms of yield, income, and catch composition). Yet, farm-aggregated fish are vulnerable to hidden fishing practices inside the farm. The analysis of the perception of marine fish farming in Catalonia was performed with five key stakeholder-groups (NGOs, local fishermen, fish farming industry, scientists and regional administration). Four perceptions were identified; two represented divergent views and two intermediate positions. Environmental impacts were not perceived as a high risk by the majority of the participants. The major weaknesses were attributed to economic (e.g. price competition with other producer countries) and social issues (e.g. lack of credible information about farmed products). Overall, this thesis provides new information about the complex dynamics of wild fish aggregations at marine fish farms and investigates how this attraction effect influences the local small-scale fishery. Moreover, an understanding of the different perceptions on marine fish farming can help to secure a social, economic and environmental sustainable activity.
Esta tesis persigue avanzar en el conocimiento de las interacciones de la piscicultura marina, de carácter multidisciplinar y estructurada en tres áreas: ecología (capítulos 1 y 2), pesca (capítulo 3) y ciencias sociales (capítulo 4). En el área de ecología, se analizó la extensión espacial y temporal del efecto atractor de peces salvajes sobre dos tipos de granjas: atún rojo (Thunnus thynnus) y dorada (Sparus aurata). En ambas el efecto atractor se restringía al límite de las jaulas, variando estacionalmente y en profundidad. Las diferencias entre granjas, permanente en doradas y estacional en atunes, se deben a diferencias en la composición específica asociadas con la localización y tipo de cultivo. El análisis de la variabilidad interna en la comunidad íctica se analizó ya que podría ser un factor distorsionador en la estimación del efecto atractor. Los resultados mostraron que la abundancia de peces en superficie disminuía significativamente en los períodos de no alimentación y durante la alimentación las concentraciones de peces disminuían en función de la distancia al barco alimentador. Por el contrario, la variabilidad de agregación en el fondo dependía exclusivamente del tipo de sustrato. La interacción con la pesca artesanal se evaluó con el fin de conocer si las granjas actúan como zonas de protección o como trampas para los peces salvajes. Los resultados no mostraron beneficio, detrimento o diferencia de la pesca en las proximidades de la granja respecto a zonas distantes (en términos de producción, ingresos y composición de las capturas). El análisis de la percepción de la acuicultura, indicador del escenario de aceptación y de elementos clave para su desarrollo, se realizó sobre cinco grupos de interés (ONGs, pescadores locales, industria de la piscicultura, científicos y administración regional) en el marco regional de Cataluña. Se identificaron cuatro percepciones; dos claramente divergentes y dos de posturas intermedias. Los impactos ambientales no fueron percibidos como de alto riesgo por la mayoría de los actores. Las principales debilidades fueron atribuidas a aspectos económicos (p. ej. la competencia con otros países productores) y sociales (p. ej. la falta de información acerca de la credibilidad de los productos acuícolas).

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VanDeHey, Justin A. "Genetic structure among Lake Michigan's lake whitefish spawning aggregates /." Link to full text, 2007. http://epapers.uwsp.edu/thesis/2007/vandehey.pdf.

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Muhling, Barbara A. "Larval fish assemblages in coastal, shelf and offshore waters of South-Western Australia /." Access via Murdoch University Digital Theses Project, 2006. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20061129.110448.

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Buch, Tanja B. "Spatial structure of North Sea fishes : theory and application to abundance estimation." Thesis, University of Aberdeen, 2018. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=237000.

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McDermott, Susanne Finckh. "Improving abundance estimation of a patchily distributed fish, Atka mackerel (Pleurogrammus monopterygius) /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/5385.

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Paxton, C. G. M. "Genetics and environmental components of behavioural variation within guppy, Poecilia reticulata, populations in Trinidad." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259896.

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Dissertations / Theses on the topic 'Fish populations'

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