Dissertationen zum Thema „Gudgeon“

Introduced species are a major threat to native biodiversity and, whilst there are socio-economic benefits often gained from introductions, there are also inherent risks to receiving ecosystems, particularly from those species that develop invasions. This is problematic, as once in the wild, their management is inherently difficult. The most effective method to avoid an invasion is preventing the initial introduction; if this is unsuccessful, then methods should aim to minimise the dispersal opportunities of the species into the wider environment. This research used the Asian fish of the Cyprinidae family, topmouth gudgeon Pseudorasbora parva, as the model species, a highly invasive fish in mainland Europe. England and Wales was the model area, where 26 P. parva populations have been recorded but the species is not yet invasive. The research identified how aspects of P. parva ecology can underpin the application of methods to prevent their wider dispersal into the environment to prevent their invasion. It covered work on: (i) the expression of their life history traits; (ii) preventing their introduction into inland waters via fish movement audits; (iii) identifying the risk of their dispersal into river catchments from aquaculture sites; and (iv) assessing how their populations can be controlled to minimise dispersal opportunities. Assessments of their somatic growth rates in relation to temperature and latitude revealed that whilst temperature was a strong regulator of growth in controlled conditions, in the wild, population density was important, with this having a stronger influence on growth rates than latitude (temperature). Individuals in recently founded populations and at low densities had very fast growth rates, with this advantageous in facilitating their establishment, with these growth rates slowing as population abundance increased. Assessments of their reproductive traits revealed that, contrary to European and Asian populations, they did not show an extended reproductive period involving fractional spawning, but instead had a discrete reproductive season that lasted no longer than three weeks in the early summer period. Approximately 8000 fish movements (i.e. removals from fisheries, stocking into fisheries) are legally consented by the Environment Agency in England each year. On each of these stockings, there is a concomitant risk of also accidentally introducing a ‘hitch-hiking’ species that has not been detected in the batch of fish. To test whether a ‘fish movement audit’ scheme could reduce this risk, an experiment was completed on batches of native fish containing known proportions of P. parva and using auditors of varying non-native fish knowledge and pre-defined searching effort levels. Outputs revealed that although the scheme could be successful at preventing 95 % of accidental introductions, this required highly experienced auditors using high searching efforts. The presence of P. parva on an aquaculture site in Southern England enabled completion of field studies on assessing their drifting rates from the farm and into an adjacent stream. Drift rates were negligible during normal summer operations. However, when aquaculture ponds on the site were drained down for husbandry purposes, the elevated flow of water displaced high numbers of mature P. parva, resulting in high dispersal rates. Whilst no P. parva were recorded in the three hours prior to ponds being drained down, over 200 were captured in drift nets in the 21 hours after draining commenced. Thus, whilst the overall risk of their dispersal was low, this was elevated considerably during specific on-site activities, and would require pro-active management to prevent accidental dispersal during these activities. A long-term field experiment, allied with a field study, revealed that in small fishing and aquaculture ponds, P. parva population densities can be maintained at very low abundances over long time periods, but required a combination of biocontrol (via manipulating of numbers of native piscivorous fish) and targeted fish removals (by trapping in spring and autumn). Fish removals alone were unable to reduce population sizes due to the compensatory responses of the remaining fish. These responses were not, however, detected when native piscivorous fish were present, probably through their predation of nest-guarding male P. parva that then inhibited large numbers of in young-of-the-year being produced. In summary, the research revealed utility of non-native fish management methods being applied to populations following their testing in more controlled conditions. It revealed that introductions into fisheries of fast growing, small-bodied, non-native fishes can be prevented by auditing, and where this is unsuccessful then their dispersal into the wider environment can be minimised, if not eliminated, by a variety of method that should reduce their invasion risk.

This study investigated the causes of high level of intra-and inter-population variation known to occur in the morphology of fish in the genus Hypseleotris Eleotride in southern Australia, particularly within the Murray-Darling river system. The three major objectives of the study were, identify the number and distribution of species,determine the genetic structure of the populations and analyse relationships between species and consider the process of speciation in this species complex. The investigation of morphological variation in Hypseleotris confirmed the presence of two well known species i.e. H. compressa and H. galli, in the coastal rivers and also of the inland species H. klunzingeri. Populations of Hypseleotris klunzigeri sensu lato in inland river were found to be very highly variable and analysis using discriminant functions and principle component analysis showed the widespread presence of three forms (A, B1 and B2). The analysis was confused by the presence of north/south clines and upstream/downstream variation in characteristic in each form. After these factors were removed, there was still a great deal of variation in each population. The presence of hybrids between each pair of inland species, identified by both morphological and genetic data, further confused the analysis and makes identification of all specimens to species in the field difficult. Examination of type material of H. Klunzingeri showed that this belonged to form B2. The other forms can be related to the undescribed species, Midgley's carp gudgeon and Lake's carp gudgeon. Keys to the species in the complex in southeastern Australia are given. The morphological and genetic data show that H. compressa and H. klunzingeri are sister species, primarily separated by the eastern uplands. Similarly, the coastal species, H. galli is related to form B1 and more distantly, to form A. Possible scenarios for the complex are given.
Doctor of Philosophy (PhD)

Thesis (Ph.D.)--University of Western Sydney, Hawkesbury, 1999.
"A Thesis submitted to the Faculty of Science and Technology in fulfilment of the requirements for the Degree of Doctor of Philosophy". "November 1999". Bibliography : leaves 147-155.

Afin de quantifier les risques d’invasion chez le goujon Asiatique Pseudorasbora parva, un petit cyprinidae d’eau douce, j’ai tout d’abord testé une approche corrélative de modélisation de la niche climatique dans laquelle j’ai intégré un proxy relatif à la probabilité d’introduction. Cette approche s’appuie sur des assomptions relatives à l’adaptation des organismes aux conditions environnementales locales ou régionales. J’ai ensuite comparé la niche climatique mesurée de deux lignées génétiques majeures à la fois dans les aires natives et envahies. Puis dans un second temps, par une approche expérimentale j’ai comparé la réponse aux variations de température, des traits d’histoire de vie de populations vivant dans des zones climatiques contrastées. Finalement, je me suis intéressé à la dispersion des goujons Asiatiques afin de mieux comprendre si les populations situées sur les fronts d’invasions avaient des capacités de colonisation plus importante. J’ai donc quantifié et comparé le long d’un gradient d’invasion, le potentiel de dispersion des individus ainsi que des traits pouvant y être liés (activité et morphologie). L’étude des risques d’invasions a montré que de nombreuses zones – au delà des zones déjà envahies - étaient climatiquement favorables au goujon Asiatique. C’était le cas en particulier pour certaines zones comme l’Australie, l’Amérique du Sud et du Nord, indiquant que l’invasion de cette espèce pourrait encore s’étendre. Après avoir pris en compte les probabilités d’introduction, cette étude a montré que l’Amérique du Nord était la zone la plus à risques. Par contre, la niche climatique entre les différentes lignées dans les zones géographiques envahies est très similaire, ce qui laisse à penser qu’il n’y a pas de patrons d’adaptation locale chez cette espèce. Pour autant, la niche climatique observée dans la zone envahie est très différente de celle observée dans la zone native, ce qui suggère un shift climatique important au cours de l’invasion. Les réponses thermiques des traits d’histoire de vie du goujon Asiatique testés expérimentalement n’ont pas varié significativement entre les populations originaires de conditions climatiques continentales et maritime-tempérées. Par exemple, l’effort reproductif global des femelles n’a pas varié entre les températures testées (15-25°C) mais la stratégie temporelle de reproduction a beaucoup varié. L’effort reproductif était plus cours et plus intense à forte température, alors qu’il était plus étalé et avec des pics reproductifs moins forts à faible température. Pour ailleurs, il semble qu’il existe un gradient morphologique fort entre les populations situées à différentes distances du front d’invasion ce qui suggère une forte plasticité morphologique mais qui ne serait pas liée à la capacité de dispersion de ces populations. En effet, cette dernière ne variant pas significativement le long du gradient d’invasion. La capacité de dispersion serait principalement liée à la taille du corps de goujon Asiatique, les individus les plus grands ayant une probabilité plus élevée de disperser.Bien que les prédictions générales du modèle de niche puissent être affectées par de potentielles adaptations à l’échelle de la population ou de la lignée évolutive, les résultats suggèrent qu’une certaine incertitude liée à ces prédictions persiste puisque la distribution native ne prédisait que très mal la distribution actuelle dans les zones envahies. Par ailleurs, mes travaux expérimentaux à plus fine échelle suggèrent que cette espèce est extrêmement adaptable et tolère une large gamme environnementale, ce qui pourrait expliquer son caractère invasif. Les connaissances produites au cours de cette thèse constituent donc des ressources extrêmement pertinentes pour développer des stratégies de gestion visant à contrôler les invasions futures du goujon Asiatique
In this thesis I set out to quantify the risk of invasion from the invasive freshwater fish, Pseudorasbora parva, at a global extent, using traditional correlative ecological niche modelling approaches with the integration of surrogate data representing introduction likelihood (Chapter I). These correlative approaches rely upon key assumptions relating to the presence or absence of local or regional adaptations, and so I subsequently tested for evidence of such adaptations in genetic lineages and in individual populations. This was achieved through analyzing climatic niche differentiation of key genetic lineages in the native and invasive ranges (Chapter II) and by conducting lab experiments comparing thermal responses of important life history traits in populations from contrasting climates (Chapter III). The initial risk assessment did not account for a key factor in invasions; namely, natural dispersal. Natural dispersal has been observed to be subject to selection in vanguard populations of invasive species, and adaptation of dispersal traits can infer additional invasive vigor, allowing the species to spread across the landscape quicker. For this reason, I quantified dispersal, activity and morphological differences, often associated with differential dispersal ability, in populations along a distance-gradient from an invasion front, in order to identify if P. parva is capable of such adaptations.The initial risk mapping study showed that large areas, beyond the current distribution of the species, are climatically suitable. These areas are mainly in North and South America, Australia and New Zealand, and constitute significant scope for spread and impact of this species. When introduction likelihood was included, N. America appears most at risk. I found no evidence to suggest that native genetic lineages represented local adaptations to their respective native climates - there was little or no differentiation of the lineages’ climatic niches in the invasive range. It was also apparent, from the niche comparisons, that the climatic niche in the invaded range constituted a significant shift, compared to the native range. The thermal responses of P. parva life history traits did not differ significantly between populations from a strongly seasonal continental climate and a mild temperate maritime climate. The overall reproductive output of females did not vary according to breeding season temperature, however, temporal reproductive strategy showed a strong response, with lower temperatures inducing a protracted breeding season and higher temperatures inducing rapid and intense reproductive output. The dispersal and morphology-related study identified a strong gradient of morphological change, corresponding with distance from invasion front. This demonstrates a high degree of plasticity in P. parva’s morphology in an invasion context, however this was not linked to either dispersal or activity levels, neither of which was significantly linked to distance from invasion front. Dispersal was best explained by body size, with larger fish more likely to disperse further.Whilst I found no evidence to suggest that the model predictions (Chapter I) were hampered by differentiation at either lineage or population levels, the findings of Chapter II do highlight the uncertainties surrounding the degree of conservatism in such predictions, mainly owing to the fact that past, native, distribution did not accurately predict the current invaded distribution. The results of Chapters II-IV show broad tolerances and great plasticity in P. parva, which likely underpin this species success as a pan-continental invader. The knowledge produced in this thesis provides a useful new resource for the development of management strategies for P. parva and could be usefully enhanced by the additional of analogous studies on native populations, which could help elucidate the source of the observed plasticity

The use of reproductive chemical cues is widespread amongst fishes. However, the most understood sex pheromone systems derive from species that employ a scramble spawning reproductive strategy. This thesis investigated for the first time the use of reproductive chemical communication in topmouth gudgeon Pseudorasbora parva (Temminck & Schlegel) and sunbleak Leucaspius delineates (Heckel) that use two different forms of a male nest guarding reproductive strategy. In topmouth gudgeon, approximately a third of reproductive females adopted a body posture in response to reproductive male conditioned water advertising high receptivity to potential mates. Electro-Olfactory Gram recordings of reproductive male and female topmouth gudgeon revealed a high magnitude response to reproductive male and female odours. In addition, both topmouth gudgeon and sunbleak reproductive females responded to chemicals cues derived from conspecific reproductive males by an increase in swimming behaviour. In contrast to male topmouth gudgeon, reproductive male sunbleak responded to chemical cues from reproductive conspecific males and females. Active compounds were isolated from reproductive male topmouth gudgeon conditioned water by two different methods solid phase extraction (C-18 cartridges) and using a freeze drier. The eluate was subsequently separated using High Performance Liquid Chromatography into retention time fractions. An active fraction was identified using a bioassay guided separation. Nuclear Magnetic Resonance analysis showed that compounds were present in the active fraction. Chemical interaction between topmouth gudgeon (invasive to Europe) and sunbleak (native to Europe) was also investigated. Behaviour responses in the two species were asymmetrical topmouth gudgeon did not respond to sunbleak chemical cues. In contrast, both reproductive female and male sunbleak responded to topmouth gudgeon chemical cues. The results show that reproductive chemical communication is in operation in both test species. The cross species interaction indicates that pheromone pollution may represent an additional impact of non-native species introductions.

Gudgeon (Hypseleotris spp.) are the most widespread and abundant native Australian freshwater fish and the dominant zooplanktivore in Maroon Dam, the site of Australia's first whole-lake biomanipulation experiment. The spatial (littoral and pelagic) and temporal (diurnal and seasonal) distribution and diet of Hypseleotris was examined following the addition of 100,000 piscivorous Australian Bass (Macquaria novemaculeata) to Maroon Dam in the summer of 1998/99. A strong spatial and temporal ontogeny was observed, with smaller (<16 mm SL) Hypseleotris dominating the pelagic, an intermediate (12-20 mm SL) size class diurnally migrating between littoral and pelagic, and larger fish (>20 mm SL) remaining in the littoral throughout the day and night. Spatial ontogeny affected diet also, with fish consuming a decreasing proportion of zooplankton and an increasing proportion of macro-invertebrates as fish length increased and habitat use changed. A bioenergetics model was constructed to examine these distribution and diet patterns. Laboratory derived consumption and respiration parameters were combined with caloric densities and commonly accepted excretion and activity scalars to produce modeled growth estimates that were validated against Hypseleotris age-at-growth data collected from a diversity of habitats. Using this model, it was concluded that the spatial and temporal ontogeny and diet of Hypseleotris in Maroon Dam described the most energetically advantageous life history. Unlike many zooplanktivores in northern hemisphere lakes, Hypseleotris did not appear to engage in migratory predator avoidance behaviour. This is discussed in a context of Australia's paucity of pelagic piscivores. It is concluded that top-down biomanipulation by stocking of native piscivores has only a limited application in Australia, and that other biomanipulation techniques may prove more successful.

Gudgeon (Hypseleotris spp.) are the most widespread and abundant native Australian freshwater fish and the dominant zooplanktivore in Maroon Dam, the site of Australia's first whole-lake biomanipulation experiment. The spatial (littoral and pelagic) and temporal (diurnal and seasonal) distribution and diet of Hypseleotris was examined following the addition of 100,000 piscivorous Australian Bass (Macquaria novemaculeata) to Maroon Dam in the summer of 1998/99. A strong spatial and temporal ontogeny was observed, with smaller (<16 mm SL) Hypseleotris dominating the pelagic, an intermediate (12-20 mm SL) size class diurnally migrating between littoral and pelagic, and larger fish (>20 mm SL) remaining in the littoral throughout the day and night. Spatial ontogeny affected diet also, with fish consuming a decreasing proportion of zooplankton and an increasing proportion of macro-invertebrates as fish length increased and habitat use changed. A bioenergetics model was constructed to examine these distribution and diet patterns. Laboratory derived consumption and respiration parameters were combined with caloric densities and commonly accepted excretion and activity scalars to produce modeled growth estimates that were validated against Hypseleotris age-at-growth data collected from a diversity of habitats. Using this model, it was concluded that the spatial and temporal ontogeny and diet of Hypseleotris in Maroon Dam described the most energetically advantageous life history. Unlike many zooplanktivores in northern hemisphere lakes, Hypseleotris did not appear to engage in migratory predator avoidance behaviour. This is discussed in a context of Australia's paucity of pelagic piscivores. It is concluded that top-down biomanipulation by stocking of native piscivores has only a limited application in Australia, and that other biomanipulation techniques may prove more successful.

The study of biological invasions is a major research topic, both because of the ecological and economical damage caused by invasive species and also as a great natural experiment to study evolutionary responses of non-native populations to their new environment, and the factors influencing invasions. Introduced species often evolve rapidly, despite the assumed loss of genetic variation associated with bottlenecks during the invasion process. In order examine the processes and mechanisms affecting the outcome invasions I studied two non-native fish species, the topmouth gudgeon (Pseudorasbora parva) is an Asian cyprinid that is found in most European countries as a result of accidental introductions. Rainbow trout (Oncorhynchus mykiss) has been introduced from the United States for aquaculture and angling, however, despite numerous introductions, it has only been able to establish in few European waters. I used mitochondrial DNA and microsatellite markers to understand the invasion history of these species and the factors that influence their establishment success/failure. Part of the cytochrome b gene was analysed in European and native Asian P. parva populations and microsatellite markers were used to investigate the source populations of the species. The analyses elucidated the colonisation pattern of P. parva in Europe and supported the hypothesis that the species spread through long-distance and stepping-stone methods and originate from admixed source populations. In O. mykiss, part of the d-loop region of the mitochondrial genome was analysed to compare the phylogeographic structure of native US and introduced European populations to examine the spread of the species outside its native range, as well as to find out whether the resistant Hofer strain is the source population of the European rainbow trout populations. I found that European populations are likely to originate from various sources, mainly from California. The Hofer strain is likely to have contributed to some of the wild European populations. Assessing the role of these processes is fundamental in understanding invasive species and finding suitable management practices to control them. From an evolutionary point of view, I was able to detect some of the processes that are important during invasions, in these studies particularly the role of multiple introductions and introduction from genetically admixed source populations.

Six rivers within the upper Mumbidgee catchment were sampled for larval and juvenile fish. The rivers represented both regulated and unregulated flow regimes and varied widely in size. There was wide variation in the larval fish communities supported by each river, both in terms of the species diversity and total abundance of fish sampled. The highly regulated reach of the Mumbidgee River sampled during this study had the highest numbers of native species and native individuals of any river sampled. In the two rivers selected for further study, the Murmmbidgee and Goodradigbee, there was a high level of inter-annual consistency in the species composition within the reaches sampled, despite considerable change in the temperature and flow regimes of both rivers. This indicates that at least some spawning of those species sampled may occur each year, regardless of environmental conditions. Estimates of the relative abundance of each species sampled changed markedly between years, and it is argued, on the basis of growth information contained in the otoliths, that differential survival of larvae and juveniles was largely responsible for this shift in relative abundance. Otolith microstructure provided information on the date of spawning and early growth patterns of all species sampled in the upper Mumumbidgee catchment. In addition to determining the age and thus 'birth-date' of an individual, the effect of a particular event or series of events has on growth, and subsequent survival, is permanently recorded in the otolith microstructure. This enables accurate back-calculation and correlation to management actions or natural events. No other research tool has this ability to retrospectively assess, on a daily basis, the impacts of management actions on condition and subsequent survival of fish larvae. Species sampled could be separated into three groups based on spawning requirements; those linked with flow, those linked with temperature and generalist species that appear to have river independent cues, such as photoperiod or moon phase. Patterns in growth rate during the early life history stages enabled quantification of the consequences of variation in environmental conditions on the survival and recruitment of various species. Growth was not always highly correlated with water temperature, in fact, for mountain galaxias, high temperatures appear to negatively affect larval condition and subsequent survival. Conversely, carp exhibited a strategy more consistent with common perceptions, with growth and survival increasing with increasing temperature. The study uncovered spawning and growth patterns that were unexpected. Age analysis of western carp gudgeon demonstrated that they had undertaken a mid-winter spawning, when the water temperature in the main channel was far lower than that at which spawning was previously recorded for this species. Redfin perch from the unregulated Goodradigbee River exhibited growth rates exceeding the published upper limits for this and other closely related species. This growth could not be correlated with either temperature or flow, indicating that there are additional factors that dominate growth rates of redfin perch in the Goodradigbee River. The proportion and abundance of native species alone is not necessarily indicative of a 'healthy' or pristine system; some native species may be positively affected by river regulation, at least as juveniles. Comparison of the current larval fish community with likely pre-European fish communities does provide an indication of change to the system. The results of this study suggest that larval fish growth rates can be strongly influenced by environmental conditions, thus providing a powerful tool for monitoring future change and the factors which cause it. This study has demonstrated the value of larval and juvenile fish age and growth information, derived from otolith microstructure techniques, for many aspects of river management. Current river management priorities for which these techniques provide unique information include the determination of environmental flow regimes and the control of undesirable exotic species such as carp.

This study investigated the causes of high level of intra-and inter-population variation known to occur in the morphology of fish in the genus Hypseleotris Eleotride in southern Australia, particularly within the Murray-Darling river system. The three major objectives of the study were, identify the number and distribution of species,determine the genetic structure of the populations and analyse relationships between species and consider the process of speciation in this species complex. The investigation of morphological variation in Hypseleotris confirmed the presence of two well known species i.e. H. compressa and H. galli, in the coastal rivers and also of the inland species H. klunzingeri. Populations of Hypseleotris klunzigeri sensu lato in inland river were found to be very highly variable and analysis using discriminant functions and principle component analysis showed the widespread presence of three forms (A, B1 and B2). The analysis was confused by the presence of north/south clines and upstream/downstream variation in characteristic in each form. After these factors were removed, there was still a great deal of variation in each population. The presence of hybrids between each pair of inland species, identified by both morphological and genetic data, further confused the analysis and makes identification of all specimens to species in the field difficult. Examination of type material of H. Klunzingeri showed that this belonged to form B2. The other forms can be related to the undescribed species, Midgley's carp gudgeon and Lake's carp gudgeon. Keys to the species in the complex in southeastern Australia are given. The morphological and genetic data show that H. compressa and H. klunzingeri are sister species, primarily separated by the eastern uplands. Similarly, the coastal species, H. galli is related to form B1 and more distantly, to form A. Possible scenarios for the complex are given.

Small cyprinid fish, the topmouth gudgeon (Pseudorasbora parva Schlegel, 1842) is considered as an undesirable fish species because it represents an important food competitor for commercial non-predatory fishes. This study was performed under pond conditions (four ponds in South Moravia and two ponds in South Bohemia) during the growing seasons in 2006 {--} 2007. The purpose of my work was to determinate the level of food competition between topmouth gudgeon and common carp (Cyprinus carpio) as a dominating pond fish species. Food selectivity was evaluated using Ivlev´s electivity index (Jacobs, 1974). The level of food competition between common carp and topmouth gudgeon was used to evaluate the index of food similarity according to Shorygin (1952). The diet of topmouth gudgeon consisted mainly of chironomid larvae and zooplankton, mostly cladocerans (Daphnia, Bosmina), detritus and periphyton (Oscillatoria, Scenedesmus, Sphaerotilus). Macrophytes, copepods and Brachionus were also ingested by P.parva but in comparatively low proportions. In contrast, carp diet consisted mainly of bottom items including chironomid larvae, macrophytes and organic debris, mainly detritus and periphyton. The food items of lesser importance were dragon fly (Anisoptera) larvae, cladocerans (Bosmina, Daphnia) and ostracods. Topmouth gudgeon competed with common carp for chironomid larvae, periphyton and detritus, for zooplankton (mainly cladocerans Daphnia, Bosmina). The highest valuation the food competition was registered in fish from the Vracovický pond (South Moravia) and the Podsedek pond (South Bohemia), when it amounted from 24.02 to 34.78 % food similarity.

This study aimed to evaluate otter predation on stocked trout and grayling. The diet composition of piscivorous Eurasian otters (Lutra lutra) was studied on the stream Chotýšanka in central Bohemia using spraint (otter faeces) analysis during one winter period (90 days). Stocking took place mostly in the second half of 2005. Around 5000 hatchery-reared brown trouts (Salmo trutta m. fario) of size about 10 cm, 600 graylings (Thymallus thymallus) of the same size and 480 rainbow trouts (Oncorhynchus mykiss) of size about 30 cm were stocked into the stream. Spraints were collected in December 2005 and January 2006. We found and identified 1531 fish in the spraints. The primary food source of otters was fish (almost 85 % of biomass). The main fish prey was small - sized, below 20 g in weight and 13 cm in length. The bulk of otter's diet consisted of less - valued species, especially the gudgeon (Gobio gobio). Other frequently consumed fish species were the European chub (Squalius cephalus), the common carp (Cyprinus carpio), the European perch (Perca fluviatilis), the brown trout and the rainbow trout. Consumption of stocked brown trout was 1,80 %, while cosumption of stocked rainbow trout was 10,90 % of biomass. Otters in this area consumed about 723 - 1446 brown trouts and 72 - 144 rainbow trouts...