Auswahl der wissenschaftlichen Literatur zum Thema „Trout habitat score“

Microhabitat use of instream wood habitat by Trout Cod Maccullochella macquariensis (Cuvier), a critically endangered species with a restricted distribution, was examined in the Murrumbidgee River in New South Wales, Australia. Habitat variables were scored or measured at 100 m intervals along the river or wherever Trout Cod were captured using electrofishing. The occurrence of Trout Cod was significantly dependent on the presence of instream woody habitat and 95% of samples where trout cod were caught were associated with the presence of woody habitat. Trout Cod were more likely to be found on simply-structured woody habitats, away from the river-bank and their abundance showed no relationship with water velocity. The low abundance of other fish species at the sampling sites suggests that the relationships demonstrated are not due to inter-species interactions. The results will assist with specific management actions to restore and protect populations of this endangered species.

This study develops a quantitative model of the combined effects of temperature and ambient dissolved oxygen on metabolic scope-for-activity and power capacity of juvenile lake trout (Salvelinus namaycush). The model provides a framework for evaluating the effects of hypoxia on the capacity of lake trout to perform critical daily life support activities. Maximum power output for sustained swimming of yearling lake trout occurred at 12–20 °C and a dissolved oxygen concentration of >7 mg·L–1. At 4–8 °C, temperatures typical of the hypolimnetic summer habitat of juvenile lake trout, maximum power capacity was reduced by 33%, 67%, and 100% at ambient dissolved oxygen concentrations of 7, 5, and 3 mg·L–1, respectively. Analysis of power outputs, growth impairment, and recruitment success indicated that attainment of 3/4 power capacity would accommodate most daily life support activities of juvenile lake trout. At 4–14 °C, the threshold dissolved oxygen concentration for attainment of 3/4 scope-for-activity varied from 7.5 to 6.6 mg·L–1, respectively, with a mean and standard deviation of 7.04 ± 0.33 mg·L–1. A dissolved oxygen criterion of 7 mg·L–1 is recommended for protection of the hypolimnetic habitat of juvenile lake trout.

Juvenile compensation in survival, quantified as compensation ratio (CR), is critical for fish population persistence. At present, no estimate of this key parameter exists for bull trout (Salvelinus confluentus). This species has a conservation listing and is targeted by recreational angling in portions of its range. Obtaining accurate estimates of CR is crucial to aid recovery efforts and develop sustainable fisheries policies. This investigation develops a hierarchical Bayesian meta-analysis to estimate CR and explore the functional form of stock–recruitment for bull trout. Results show bull trout have high scope for density-dependent compensation evidenced by CR estimates generated herein and by previous research. This demonstrates changes in habitat quality and quantity are likely limiting recovery of many populations. However, owing to lack of data, variance is high. Limitations in available data for this analysis are due to the high cost and operational difficulty of sampling, and high uncertainty in CR estimates. This study highlights the importance of collecting additional paired stock–recruitment data to facilitate future investigations and reduce variance in CR estimates for bull trout.

Rainbow trout (Oncorhynchus mykiss) has become by far the most frequently farmed freshwater fish species in Turkey, whereas very little is known about its establishment and invasiveness potential. We explored this potential through a combination of Maxent habitat suitability model and the Aquatic Species Invasiveness Screening Kit (AS-ISK) on the river basin scale by generating an overall risk score (ORS). The outcome of this approach was also incorporated with the spatial analysis of native salmonid species by generating a relative vulnerability score (RVS) to prioritize susceptibility of native species (or populations) and to propose risk hotspots by identifying their potential geographic overlap and interaction with O. mykiss. Results suggest that the northern basins (Eastern Black Sea, Western Black Sea and Marmara basins) are the most suitable basins for O. mykiss. According to the Basic Risk Assessment (BRA) threshold scores, O. mykiss is classified as “high risk” for 3 (12.0%) of the 25 river basins screened (Western Black Sea, Eastern Black Sea and Maritza-Ergene), and as “medium risk” for the remaining basins. The climate change assessment (CCA) scores negatively contributed the overall invasiveness potential of O. mykiss in 22 (88.0%) of the river basins and resulted in zero contribution for the remaining three, namely Aras-Kura, Çoruh river and Eastern Black Sea. The ORS score of river basins was lowest for Orontes and highest for Western Black Sea, whereas it was lowest for Konya-closed basin and highest for Eastern Black Sea, when CCA was associated. The micro-basins occupied by Salmo rizeensis had the highest mean habitat suitability with O. mykiss. Among the all species, S. abanticus had the highest RVS, followed by S. munzuricus and S. euphrataeus. The overall outcome of the present study also suggests that the establishment and invasiveness potential of O. mykiss may decrease under future (climate warmer) in Turkey, except for the northeast region. This study can provide environmental managers and policy makers an insight into using multiple tools for decision-making. The proposed RVS can also be considered as a complementary tool to improve IUCN red list assessment protocols of species.

The physiology and behaviour of fish are strongly affected by ambient water temperature. Physiological traits related to metabolism, such as aerobic scope (AS), can be measured across temperature gradients, and the resulting performance curve reflects the thermal niche that fish can occupy. We measured AS of westslope cutthroat trout (Oncorhynchus clarkii lewisi) at 5, 10, 15, 20, and 22 °C and compared temperature preference (T pref) of the species with non-native brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout (Oncorhynchus mykiss). Intermittent-flow respirometry experiments demonstrated that metabolic performance of westslope cutthroat trout was optimal at ∼15 °C and decreased substantially beyond this temperature, until lethal temperatures at ∼25 °C. Adjusted T pref across species were comparatively high, ranging from 17.8 to 19.9 °C, with the highest T pref observed for westslope cutthroat trout. Results suggest that although westslope cutthroat trout is considered a cold-water species, they do not prefer or perform as well in cold water (≤10 °C) and thus can occupy a warmer thermal niche than previously thought. The metabolic performance curve (AS) can be used to develop species‐specific thermal criteria to delineate important thermal habitats and guide conservation and recovery actions for westslope cutthroat trout.

Vattenkraftens ska förses med moderna miljövillkor i linje med miljöbalken. Ett av underlagen som föreslås vara nödvändigt inför prövningen är kännedom var det finns strömmande vatten och olika typer av habitat, något som inte finns i alla avrinningsområden. Arbetets syfte var därför att testa och utvärdera metoder som med begränsat underlag kan användas för att identifiera lax- och öringshabitat samt utreda sträckornas habitatskvaliteten.  För att genomföra detta genomfördes först en lutningsanalys där vattendragets strömsträckor identifierades genom att utifrån lantmäteriets höjdmodell, bestämma lutningen i vattendraget. Därefter bestämdes beskuggningsgraden vid strömsträckorna genom att studera flygbilder följt av parametrarna vattenhastighet, bredd och djup beräknades med MSB:s hydrauliska modell. På detta applicerades trout habitat score och laxhabitatklass, två bedömningssystem som används för att kvalitetsbestämma habitat utifrån fiskens habitatspreferenser för ovannämnda parametrar. Den predikterade habitatskvaliteten validerades sedan mot redan kända habitat som karterats i fält då vattendraget biotopkarterades.  Med lutningsanalysen identifierades strömsträckor där samtliga kända habitat som karterats som bra eller mycket bra identifierades. Metoden fungerade således bra för att identifiera strömmande vatten. Det finns dock svagheter eftersom metoden inte nödvändigtvis säger något direkt om strömsträckornas habitatskvalitet, men tillsammans med andra metoder så som lokalkännedom kan borde den vara till nytta att på ett enkelt sätt få en bra bild över utbredningen av vattendragets strömsträckor. När habitatskvaliteten beräknades vid strömsträckorna underskattades i de flesta fall. Vad detta beror på går inte att svara på utan vidare undersökning, men det finns mycket som pekar på att det är till följd av att den hydrauliska modellens rumsliga skala samt kalibrering. Det finns således stora osäkerheter med att använda MSB:s hydrauliska modell i habitatkarteringssyfte.
Hydropower is vital for Sweden. Not only does it provide Sweden with around 40% of the annual electricity production and supply the electric grid with system services, but the energy is also to be concerned as renewable with no greenhouse gas emissions. However, the hydropower plants and its dams create environmental problems for the aquatic life in the lake and streams. Moreover, little to no measures have been implemented as most powerplants come from a time where the concern and requirements for environmental mitigation measures were considered. Sweden’s hydropower is therefore to apply for new water permits in line with the Swedish environmental code, likely to result in many powerplants having to implement mitigation measures to lower their impact on the aquatic life. In this work, data on river habitats must compiled, however, the extent to which this data exists varies between different river basins. In river basins where the level of this kind of knowledge is low there is a need for cost-effective ways to investigate this matter.  The aim of the thesis was to test and evaluate methods that can be used to identify in stream habitats for trout and salmon parr and assess the quality of these habitats using data which is highly available for many river basins.  First a slope analysis was conducted in GIS, to identify rapids in the study area. The method is based on calculating the average slope along the river using the national terrain model. Once rapids were identified, aerial footage was studied to determine the rate of shadow cast on the watercourse and a free to use hydraulic model was used to calculate water velocity, depth, and top width at the rapid locations. Later, the above-mentioned parameters were combined using two methods, trout habitat score and salmon habitat class, to rate the rapids’ functionality as habitat for salmon and trout parr. Finally, the habitat location and quality of the identified rapids were validated against already known habitats, mapped with conventional habitat mapping methods.  Using the slope analysis, all known habitats were identified. However, there were a few uncertainties as several river stretches, not mapped as habitat, also were identified. These wrongly identified rapids were for the most part to be regarded as moderately flat and could be excluded using aerial photographs. When it comes to the predicted habitat quality, it can be concluded that it generally was underestimated when compared to the habitat quality from the habitat mapping. The reasons for this were not fully investigated in this thesis, however much points towards weaknesses related to the hydraulic model as it primarily was hydraulic parameters such as depth and top width that was underestimated.  The thesis conclude that the slope analysis is a strong tool when it comes to locating in stream habitats using sparse data and has good potential as a screening tool, but one must be aware of the method’s short comings. The hydraulic model on the other hand, shouldn’t be used in its original form to investigate habitat quality.

<i>Abstract.</i>—Fish assemblages in the Willamette River basin (Oregon) were once substantially degraded by water pollution, channelization, dams, nonnative fish, and conversion of natural forest and savanna to agriculture and urbanization. Restoration actions have included basinwide waste treatment, physical habitat rehabilitation, recovery of the Oregon Chub <i>Oregonichthys crameri</i> to stable status, and stocking reductions of nonnative fish to protect native fish. State and federal sewage treatment regulations and funding, federal endangered species regulations and funding, and reduced funding and support for stocking nonnative trout led to those rehabilitated fish assemblages. Periodic fish and habitat monitoring has documented the following improvements in fish assemblages: (1) decreased occurrences of pollution-tolerant species and increased occurrences of pollution-sensitive species and native main-stem species, (2) increased number of abundant Oregon Chub populations, and (3) persistence of resident native Rainbow Trout <i>Oncorhynchus mykiss</i>. Notably, no known extinctions of native fish species have occurred in the Willamette River, water quality index scores in the lower river have improved from poor to fair, and water quality in the upper river remains good to excellent. In conclusion, enactment of laws and regulations for environmental protection and the collective actions of state and federal agencies, tribes, municipal governments, universities, land trusts and conservation groups, watershed councils, and private landowners have led to a substantially rehabilitated river. However, population and economic growth, climate change, nonnative fish, winter steelhead (anadromous Rainbow Trout) and spring Chinook Salmon <i>O. tshawytscha</i> listings, a superfund site, channel alterations, toxic substances, poor fish passage at dams, and altered flow regimes remain challenges. Four lessons learned are that (1) pollution control and improved water quality and flows are essential to the recovery and persistence of native fish populations, (2) recovery of endangered species is achievable but requires knowledge of their life history needs, (3) the greater ecological fitness of native stocks facilitates their persistence, and (4) research and monitoring, combined with public communication and collaboration, are essential for habitat and native fish assemblage rehabilitation.

<i>Abstract</i>.—The Vindel River (Vindelälven), Sweden, is 450 km long with a mean annual discharge of 190 m³/s and runs through sparsely populated areas in northern Sweden, joining the Ume River near the Baltic Sea. A severe decline in Atlantic Salmon <i>Salmo salar</i> and Brown Trout <i>S. trutta</i> during the past century was caused by (1) intense timber-floating activities starting in the mid-1800s, which degraded stream habitat; (2) hydropower development in the early 1900s, which limited or blocked upstream migration; and (3) an expanded coastal/ocean fishery after 1950, which overharvested anadromous populations. Restoration efforts during the 1970s and 1980s failed due to low efficacy of stocking programs and insufficient habitat restoration. A legislative reform to unify the fishery right owners (FROs) along the river helped initiate restoration efforts in the late 1990s, focusing on improving fish migration past a hydropower station and restoring degraded habitat. Sweden’s membership in the European Union made large funding for restoration projects possible. The number of returning Atlantic Salmon increased significantly after migration conditions improved around the hydropower station and with stricter regulations on the offshore fishery. Successful habitat restoration was based upon gaining trust from landowners and FROs via extensive communication to gain access to their land. Restoration work was adaptive and experiences gained were incorporated into restoration guidelines. Involvement of universities, as a provider of expertise and as an unbiased interpreter of data, provided support to legal processes and when evaluating restoration measures. During the course of the restoration work, managers learned that stocking often did not produce satisfactory results. By studying historical documents from the timber-floating era, managers learned that the scope of modifications of the tributaries had been much greater than previously thought and that habitat restoration needed to be extensive. In many tributaries, the number of juvenile Brown Trout increased significantly after habitat restoration, sometimes dramatically exceeding expectations, which made the managers question the validity of established production estimates for northern boreal streams. The experience and knowledge gained from the Vindel River restoration served as the catalyst for many other major restoration projects in rivers emptying into the Baltic Sea.