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[The spring presence of two individuals of the Sea lamprey, Petromyzon marinus, in the River Mignone near Tarquinia (Northern Lazio) could highlight a new Italian reproductive site of this rare and endangered species. This exceptional possibility could certainly be favored by the good quality of both the waters of the Mignone, and the environmental context of the record, but would require the urgent equipment of the barrier of Le Mole with a fish ladder in order to allow the sea lamprey’s upstream migration towards the areas of the upper course, even more suitable for their reproduction]. [Article in Italian]

In Lake Nojiri, the Japanese smelt, Hypomesus nipponensis McAllister, 1963, population has been thought to be maintained by artificial spawning, and stocking efforts as natural spawning in in-flowing streams is unlikely due to the lack of inflowing stream habitat. In this study, novel resident Japanese smelt spawning was observed along the lakeshore in shallow areas with clean gravel and flow. Spawning occurred at night during early March to mid-April and eggs, confirmed on gravel substrate, progressed to the eyed state in 5–6 weeks. Although natural spawning was observed, the ratio of eggs that progressed to the eyed stage was minimal, possibly due to thick algae cover in areas with low flow velocity. Therefore, resident Japanese smelt spawning along the lake shoreline is physically possible and potentially contributes to the overall population in Lake Nojiri, but in-lake spawning alone presumably is not a biologically viable method for population sustainability due to low survival rates and egg density at present. Environmental improvements such as construction of fish ladders to suitable in-flowing spawning habitat, introduction of clean gravel to shorelines, and water level management adjusted to the smelt spawning run would contribute to higher recruitment by natural smelt reproduction, and consequently enhance the smelt production in Lake Nojiri.

The development of waterways or dam constructions without doing an environmental impact assessment (EIA) and fish ladder construction, alteration of the aquatic environment, degradation of the quality of environmental variables, habitat modification, and increasing fishing pressure have accelerated the vulnerability of fish in Nepal. To assess the impact of Betani River Dam on fish diversity and environmental parameters two major sampling stations were allocated along the sampling stretch with equal four sub-stations. Four sub-stations at the upstream and four at the downstream. Sampling was conducted monthly from August 2020 to January 2021. A total of 6088 individuals, representing 29 species, were recorded in all catch samples. The species comprised 20 genera, 13 families and four orders. Of 29 fish species, the similarity percentage analysis (SIMPER) indicated that Puntius sophore (22.04%), P. ticto (10.67%), Lepidocephalus guntea (9.27%), Danio devario (8.02%), Puntius terio (7.52%), Barilius barila (6.49%) and Mystus tengera (6.32%) were the major contributing fish species reported from Betani River. Analysis of similarity (ANOSIM) for space and time indicated that there was a significant difference in spatial variation (R = 0.1946, P = 0.0001), but none was recorded in time variation (R = 0.01703, P = 0.3). One way analysis of similarity (ANOSIM) on the non-metric multidimensional scaling (NMDS) pointed a significant difference (R=0.29, P=0.0001) between upstream and downstream of fish community structure in Betani River.

A fish ladder, weir, and raceway at Whitlock Spawning Station are used to capture and retain feral fall Chinook salmon (Oncorhynchus tshawytscha) for spawning from Lake Oahe, South Dakota. Nearly 40% of the salmon ascending the fish ladder have been documented to escape from the holding raceway by descending the ladder. This manuscript describes modifications to the weir that eliminated nearly all escapements, except for an inconsequential number of small non-spawning fish. The modified design using the existing structure incorporated free-swinging, spaced steel bars with a back-stop to create a one-way gate. The modified gate does not require springs, hydraulics, or electrical power. It is relatively simple to construct and requires minimal maintenance.

The study of correlations between fish diversity, environmental variables and fish habitat aspects at different space and time scales of Nepal’s rivers and streams is scanty. This study investigated spatial and temporal patterns of fish assemblage structure in Nepal’s Andhi Khola. The field survey was conducted from September 2018 to May 2019 and the fishes were sampled from three sites using a medium size cast net of mesh size ranging from 1.5 to 2.5 cm and gill net having 2-3 cm mesh size, 30-35 feet length and 3-4 feet width, with the help of local fisher man. A total of 907 individuals representing 15 species belonged to four orders, six families and 11 genera were recorded during the study time. To detect the feasible relationships between fish community structure and environmental variables, we executed a Canonical Correspondence Analysis (CCA). Based on similarity percentage (SIMPER) analysis, the major contributing species are Barilius barila (26.15%), Barilius vagra (20.48%), Mastacembelus armatus (8.04%), Puntius terio (6.64%), and Barilius bendelisis (5.94%). One-way analysis similarity (ANOSIM) tried out for both time and space variations in fish community structure suggested that there was a significant difference in temporal variation (R = 0.794, P = 0.0037) but no significant difference in spatial variation (R = -0.18, P = 0.923). Results from the Canonical Correspondence Analysis (CCA) vindicated that dissolved oxygen, free carbon-dioxide and total hardness were the principle physio-chemical correlates of fish assemblage structure. One-way analysis of similarity (ANOSIM) on the Non-metric Multidimensional Scaling (NMDS) showed significant difference between spring, autumn and winter season but no significant difference was found in spatial variation. The extraction and transportation of boulders, cobbles, pebbles, sand mining, haphazard ongoing road development and dam construction for the irrigation without fish ladders were found to be existing threats to the fish diversity of Andhi Khola. Keywords: Fish assemblage, multivariate analysis, rivers, spatio-temporal, streams

Made available in DSpace on 2021-06-25T12:22:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-10-10 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) This study was conducted to investigate fish eggs and larvae dispersal in a river stretch influenced by small hydropower plants in Southeast Brazil. The main hypothesis is that the downstream dispersal of free-flowing eggs and larvae is likely to occur given the small size of the studied reservoirs and that passage through the dam may occur, with the fish ladder contributing to it. Eggs and larvae were collected fortnightly, between November 2016 and February 2017, from locations upstream of two dams, including lotic, transition and lentic zones. Additional samples were collected inside the fish ladders at each dam. Downstream dispersal of eggs and larvae was influenced by a combination of rainfall/flow variation and stage of the reproductive cycle, with the peak of rainfall during the summer coinciding with higher abundances. Under these conditions, eggs and larvae drifted downstream through the reservoirs and reached the dams. Once in the dam, they could pass through the fish ladder. This passage was correlated with larval density in the reservoir immediately upstream, although at very low densities compared with the other sampling sites located upstream of the fish ladders. Univ Estadual Paulista, Inst Biociencias, Dept Zool, Programa Posgrad Ciencias Biol Zool, Botucatu, SP, Brazil Charles Sturt Univ, Inst Land Water & Soc, Albury, NSW, Australia Swiss Fed Inst Technol, Dept Civil Environm & Geomat Engn, Stocker Lab, Inst Environm Engn, Zurich, Switzerland Univ Estadual Maringa, Programa Posgrad Ecol Ambientes Aquat Continentai, Nucleo Pesquisas Limnol Ictiol & Aquicultura, Maringa, Parana, Brazil Univ Estadual Paulista, Inst Biociencias, Dept Zool, Programa Posgrad Ciencias Biol Zool, Botucatu, SP, Brazil

The seasonal pattern and the composition of downstream drift of fish eggs and larvae through the fish ladder of the Porto Primavera dam, located in the Upper Parana River, Brazil, were studied. Add...

Bergan, M.A. & Kjøsnes, A. J. 2022. Ungfisktellinger som kvalitetssikring av tiltak knyttet til vandringsveiene for sjøørret i Florbekken i Stjørdalselva. NINA Rapport 2150. Norsk institutt for naturforskning. Det er gjennomført ungfisktellinger av laks og ørret i Florbekken høsten 2021. Undersøkelsene er gjennomført for å kvalitetssikre om en nybygd fisketrapp nedstrøms E14 fungerer etter hensikten. Hensikten med fisketrappa er å gi fri vandringsvei for gytefisk av fortrinnsvis sjøørret forbi E14 og opp til viktige gyteområder i bekken. Florbekken er en liten sidebekk til Stjørdalselva, Trøndelag. Bekken har svært god vann- og habitatkvalitet, og har tidligere vært en viktig gytebekk for hovedsakelig sjøørret i Stjørdalselva. Likevel har Florbekken vært fisketom i lang tid, som følge av sumbelastninger av elveforbygning i Stjørdalselva og en høy veifylling med vandringstoppende kulvert under E14. Disse inngrepene har stengt anadrom laksefisk ute fra bekken, og medført at gode gyte- og oppvekstområder har vært tapt for sjøørret. Det ble derfor byttet kulverter under E14 og Melmyrvegen i 2017/2018, og bygd fisketrapp i løpet av året 2019. Dermed ble det lagt til rette for fiskevandringer i nedre del av bekken, på strekningen fra samløpet med Stjørdalselva og opp forbi veianlegget E14/Melmyrvegen. Undersøkelsene i 2021 er entydige i resultatene, og viser at gytefisk av sjøørret har passert E14 året før. Årsyngel av ørret, som er en nøkkelindikator på at tiltaket er vellykket, dominerer ungfiskbestanden ovenfor E14. Videre øker tettheten oppover i bekken ovenfor hhv. E14 og Melmyrvegen, jo nærmere man kommer lite berørte bekkepartier med gode gyteområder og naturlig grense for anadrom strekning. Det ble også registrert nyanlagte gytegroper fra stor fisk ovenfor fisketrappa i 2021, som viser at gytefisk dermed også hadde tilgang til bekken ovenfor trappa denne høsten. Ved bruk av forventningsverdier for samlet tetthet av ungfisk som kvalitetselement på økologisk tilstand i Florbekken, så har tiltaket ved vandringsveiene gjort at bekken oppnår miljømålet etter vannforskriften i 2021. Fra å være fisketom og klassifisert til «Svært dårlig» økologisk tilstand som følge av menneskeskapte inngrep før tiltak, har Florbekken nå oppnådd miljømålet minimum «God» økologisk tilstand i 2021. Dersom vandringsveien forblir intakt i årene som kommer, kan bekken stabilisere seg på en økologisk tilstand mellom «God» og «Svært god». Tiltaket har gitt frie vandringsveier for sjøvandrende laksefisk, men har også gjort det mulig for ål å passere tiltaksområdet. Utforming av tidligere kulvert, med utstikkende åpning og høyt sprang, gjorde at ål mest sannsynlig måtte passere over selve veianlegget (E14 og Melmyrvegen) før tiltaket, noe som trolig ikke lot seg gjøre. Ål vurderes derfor nå å ha tilgang til Florbekken ovenfor E14, samt Flortjønna og eventuelt andre tilknyttede tjern i nedbørfeltet. I forbindelse med undesøkelsene avdekkes det fare for vandringsproblemer lengre opp i Florbekken for både gytefisk og ungfisk knyttet til en eldre avlingsvei like ovenfor E14 og Melmyrvegen. Kulverten under denne veien er underdimensjonert, og er i ferd med å gå tett. Kulverten og avlingsveien er etterlatenskaper fra en nedlagt virksomhet, og har ingen hensikt lenger. Inngrepet bør fjernes fra bekkeløpet.

Artificial water bodies like ditches, fish ponds, weirs, reservoirs, fish ladders, and irrigation channels are usually constructed and managed to optimize their intended purposes. However, human-made aquatic systems also have unintended consequences on ecosystem services and biogeochemical cycles. Knowledge about their functioning and possible additional ecosystem services is poor, especially compared to natural ecosystems. A GIS analysis indicates that currently only ~ 10% of European surface waters are covered by the European Water Framework directive, and that a considerable fraction of the excluded systems are likely human-made aquatic systems. There is a clear mismatch between the high possible significance of human-made water bodies and their low representation in scientific research and policy. We propose a research agenda to build an inventory of human-made aquatic ecosystems, support and advance research to further our understanding of the role of these systems in local and global biogeochemical cycles as well as to identify other benefits for society. We stress the need for studies that aim to optimize management of human-made aquatic systems considering all their functions and to support programs designed to overcome barriers of the adoption of optimized management strategies. MK and PSK were financially supported by the German Research Foundation (DFG) (project TregaTa, KO 1911/6- 1). JH was financially supported by the Grant Agency of the Czech Republic, project no. 17-09310S. RM was supported by project C-HydroChange funded by the Spanish Ministry of Economy, Industry and Competitiveness (CGL2017-86788-C3-2-P). AL was supported by Estonian Research Council Grants PSG 32 and IUT 21-2 of the Estonian Ministry of Education and Research. This study benefitted from the collaborative environment of the GLEON network. MK and PSK were financially supported by the German Research Foundation (DFG) (project TregaTa, KO 1911/6- 1). JH was financially supported by the Grant Agency of the Czech Republic, project no. 17-09310S. RM was supported by project C-HydroChange funded by the Spanish Ministry of Economy, Industry and Competitiveness (CGL2017-86788-C3-2-P). AL was supported by Estonian Research Council Grants PSG 32 and IUT 21-2 of the Estonian Ministry of Education and Research. This study benefitted from the collaborative environment of the GLEON network.

Habitat fragmentation caused by damming can greatly reduce the population viability of aquatic organisms, with smaller fragmented populations at higher risk of extinction due to increased demographic, genetic, and environmental stochasticity. However, empirical evidence demonstrating that smaller natural populations are more vulnerable to extinction is limited. We studied the vulnerability to extinction of white-spotted charr (Salvelinus leucomaenis) populations in 30 dammed-off streams in Oshima Peninsula, southwestern Hokkaido Island, Japan, by comparing the incidence of charr populations in streams between 1999 and 2014. Using electrofishing and environmental DNA surveys, we identified three localized extinctions, with the probability of extinction increasing with decreasing watershed area (our surrogate for habitat size). We also found a new population in one dammed-off stream in which white-spotted charr were previously unknown, after installation of a fish ladder, indicating the capacity of white-spotted charr to recolonize reconnected habitat in a short period. Our results suggest that localized extinction of white-spotted charr in small dammed-off streams is ongoing, but that appropriate fish migration corridors can reduce localized extinction risk and increase the probability of species persistence.

—Data based on the results of published, unpublished, and questionable materials concerning the occurrence of anadromous sturgeons after damming of the Don River downstream and upstream of the Tsimlyansk hydroengineering complex are presented. Two peaks of approaches of spawners to the dam in the 1950s and 1980s were recorded. The first peak was related to the wild population that existed in these years; the second peak was a result of mass artificial propagation. At the first stage, the Russian sturgeon (Acipenser gueldenstaedtii Brandt et Ratzeburg, 1833) and the beluga sturgeon (Huso huso (Linnaeus, 1758)) prevailed downstream from the dam; at the second stage, only the Russian sturgeon was recorded. Since 1955, only 21 individuals of anadromous sturgeons have made it through the dam by a fish ladder. During the years 1952–1961, 1145 individuals were transported into the reservoir, including 218 ind. of beluga. Some individuals of beluga were transported later as well. There are data indicating the presence of juvenile beluga individuals that originated from natural spawning in the reservoir before the 1970s. The last known spawners of Russian sturgeon and stellate sturgeon (Acipenser stellatus Pallas, 1771) in the reservoir were recorded in the 1980s or 1990s. Solitary beluga individuals may occur nowadays. It is suggested that the youngest of the noted individuals belong to the generations of the early 1990s. It is concluded that the extremely innumerous landlocked form of the Azov beluga may still exist in the reservoir.

Building dams for hydroelectric use causes several negative effects on the aquatic fauna with special attention to fish communities. In fact, among other impacts, dams act as a barrier for migratory fish, causing discontinuities in rivers and not allowing fish to move to the headwaters to breed and back to the lower portions of rivers, to grow. For more than 300 years, fishways have been used to minimize the impact of dams. Here, we assess the worldwide knowledge about fishways, identifying the temporal and spatial pattern and the situation of Brazil in this global pattern. For this, we conducted scientometric research on the Web of Science repository with the following words: weir, fish, facilities, ladder, pass, dam, fish ladder, fish pass, fishway, hydropower, Petromyzon, and salmon between 1985 and 2019. Initially, we obtained 1282 articles. After a selection, 324 articles aimed to describe fishway efficiency and the relationship with the fish fauna remained. Most of the articles on dams, fishways, and fish are from North America and Europe. Among the articles in South America, most are from Brazil. Nonetheless, information on the topic is incipient in Brazil, since the country has one of the biggest hydropower in the world and 42 scientific articles about fishways published in the international scientific database. Ecology is the area of knowledge with most articles, with continuous growth in the last 10 years. Studies in the field of ecology are strategical, as this field can integrate different areas of knowledge to test the efficiency of fishways in fish conservation and may be able to answer the question: "Are fishways an ecological trap?" Research focusing on this question is important to understand the efficiency of fishways to better evaluate solutions to minimize the negative effects of dams on fish and increase the effectiveness of fishways.

Diese Arbeit beschäftigt sich mit einer Neuinterpretation von Organismenaufstiegshilfen neben/in Querbauwerken in Flüssen oder Bächen aus Sicht einer nachhaltigen, kommerziellen Nutzung. Hauptaugenmerk wird dabei auf die Umsetzung bei beengten Platzverhältnissen ebenso gelegt, wie auf die Möglichkeit einer Dreifachnutzung zur Stromerzeugung und der touristischen Nutzung. Die Untersuchung vergleicht Vor- und Nachteile von etablierten Systemen, analysiert deren Stärken und Schwächen und extrahiert daraus eine sinnvolle Nische für diese Neuinterpretation. Um die Wirtschaftlichkeit des neuen Systems in einen realen Rahmen zu setzen, wird dieses als hypothetische Anlage in einen realen Bachverlauf in Oberösterreich gesetzt und anhand einer hydraulischen Berechnung die Auswirkung auf den Bachlauf beurteilt, der mögliche Gewinn aus dem Verkauf der gewonnenen Energie reflektiert und grundsätzliche Überlegungen zu ausschreibungsrelevanten Punkten ausgeführt. Die Arbeit dient als Vorstudie zu einem, von anderer Stelle auszuführenden, Feldversuch der in dieser Arbeit neu entwickelten Aufstiegshilfe. This thesis deals with a reinterpretation of organism ascent aids next to / in transverse structures in rivers or streams from the perspective of sustainable, commercial use. The main focus is placed on the implementation in tight spaces as well as on the possibility of triple use for power generation and tourist use. The study compares the advantages and disadvantages of established systems, analyzes their strengths and weaknesses and extracts a meaningful niche for this reinterpretation. To eveluate the economic efficiency of the new system in reference to existing ones, it is set as a hypothetical system in a real stream course in Upper Austria. To see the effects on the stream a hydraulic calculation is assessed, the possible profit from the sale of the energy obtained and reflected and basic considerations carried out on points relevant to the tender. The work serves as a preliminary study for a field test of the ascent aid newly developed in this work to be carried out elsewhere. vorgelegt von: Martin Mejstrik Auch als Printexemplar in der Bibliothek verfügbar Masterarbeit Wien, FH Campus Wien 2021

Determining the number of fish that use a fishway is essential to fisheries management but counting all fish can be impracticable due to labor and cost. We present the daily run-size estimation (DARSE) method, which uses systematic sampling to estimate the number of fish per species that pass through a fishway daily (daily run size, D). The DARSE method makes it possible to determine the minimum fraction of each hour (or hourly samples) of the day necessary to estimate D with known accuracy. We apply DARSE to each of the seven most abundant fish species (other species grouped under ‘Others’) recorded in video images taken during 46 days of one year at the Igarapava Fish Ladder, Brazil. Accuracy in estimating D was influenced by the fraction of the hour sampled and the temporal pattern of fish passage through the fishway. For species with a more uniform temporal pattern of passage, the DARSE method reduced the time spent on sampling by up to 96%, depending on the accuracy used to estimate D. Some of these species required counts of fish that pass in a fraction of an hour for all hours of the day while counts for other species can be done every 2 hours or, more rarely, every 3 hours. For species with a more aggregated temporal pattern of passage, it was possible to estimate D by sampling a fraction of an hour but with reduced accuracy in the estimation of D and little reduction in sampling time.

Hydropower plants create blockages in fish migration routes. Fish ladders can serve as alternative routes but are complex to install and follow up to help adapt and develop them further. In this study, computer vision tools are considered in this regard. More specifically, object detection is applied to images collected in a hydropower plant fish ladder to localise and classify wild, farmed and unknown fish labelled according to the presence, absence or uncertainty of an adipose fin. Fish migration patterns are not deterministic, making it a challenge to collect representative and balanced data to train a model that is resilient to changing conditions. In this study, two data imbalances are addressed by modifying a YOLOv3 baseline model: foreground-foreground class imbalance is targeted using hard and soft resampling and positional imbalance using translation augmentation. YOLOv3 is a convolutional neural network predicting bounding box coordinates, class probabilities and confidence scores simultaneously. It divides images into grids and makes predictions based on grid cell locations and anchor box offsets. Performance is estimated across 10 random data splits and different bounding box overlap thresholds, using (mean) average precision as well as recall, precision and F1 score estimated at optimal validation set confidence thresholds. The Wilcoxon signed-ranks test is used for determining statistical significance. In experiments, the best performance was observed on wild and farmed fish, with F1 scores reaching 94.8 and 89.0 percent respectively. The inconsistent appearance of unknown fish appears harder to generalise to, with a corresponding F1 score of 65.7 percent. Soft sampling but especially translation augmentation contributed to enhanced performance and reduced variance, implying that the baseline model is particularly sensitive to positional imbalance. Spatial dependencies introduced by YOLOv3’s grid cell strategy likely produce local bias or overfitting. An experimental evaluation highlight the importance of not relying on a single data split when evaluating performance on a moderately large or custom dataset. A key challenge observed in experiments is the choice of a suitable confidence threshold, influencing the dynamics of the results. Vattenkraftverk blockerar fiskars vandringsvägar. Fisktrappor kan skapa alternativa vägar men är komplexa att installera och följa upp för vidare anpassning och utveckling. I denna studie betraktas datorseende i detta avseende. Mer specifikt appliceras objektdetektering på bilder samlade i en fisktrappa i anslutning till ett vattenkraftverk, med målet att lokalisera och klassificera vilda, odlade och okända fiskar baserat på förekomsten, avsaknaden eller osäkerheten av en fett-fena. Fiskars migrationsmönster är inte deterministiska vilket gör det svårt att samla representativ och balanserad data för att trana en modell som kan hantera förändrade förutsättningar. I denna studie addresseras två obalanser i datan genom modifikation av en YOLOv3 baslinjemodell: klass-obalans genom hård och mjuk återanvändning av data och positionell obalans genom translation av bilder innan träning. YOLOv3 är ett convolutional neural network som simultant förutsäger avgränsnings-lådor, klass-sannolikheter och prediktions-säkerhet. Bilder delas upp i rutnätceller och prediktioner görs baserat på cellers position samt modifikation av fördefinierade avgränsningslådor. Resultat beräknas på 10 slumpmässiga uppdelningar av datan och för olika tröskelvärden för avgränsningslådors överlappning. På detta beräknas (mean) average precision, liksom recall, precision och F1 score med tröskelvärden för prediktions-säkerhet beräknat på valideringsdata. Wilcoxon signed-ranks test används för att avgöra statistisk signifikans. Bäst resultat observeras på vilda och odlade fiskar, med F1 scores som når 94.8 respektive 89.0 procent. Okända fiskars inkonsekventa utseenden verkar svårare att generalisera till, med en motsvarande F1 score på 65.7 procent. Mjuk återanvändning av data men speciellt translation bidrar till förbättrad prestanda och minskad varians, vilket pekar på att baslinjemodellen är särskilt känslig för positionell obalans. Spatiala beroenden skapade av YOLOv3s rutnäts-strategi producerar troligen lokal partiskhet eller överträning. I en experimentell utvärdering understryks vikten av multipel uppdelning av datan vid evaluering på ett måttligt stort eller egenskapat dataset. Att välja tröskelvärdet för prediktions-säkerhet anses utmanande och påverkar resultatens dynamik.

Various impacts of dams on aquatic organisms have been well documented in the recent past. The construction of a dam can make significant changes in the ecosystem of a river and particularly affect fish communities including obstruct the upward migration, reduce the genetic diversity and affect morphology, reproduction and growth indices, etc. After China and Turkey, Iran is the third country in dam construction in the world. Construction of dams is essential for socio-economic development in an arid country like Iran. Dams construction started since 1950s in Iran, which to date there are more than 600 (big and small) constructed dams reported from the country. Despite various benefits, construction of dams has also many assessable negative environmental impacts particularly on fishes. About 300 fish species (≅ 100 endemics) listed from water basins of Iran, which the fauna is mostly affected by the dams. The damming and its effects on fish populations in Iran is reviewed. As a result, almost no environmental considerations (in relation with ichthyofauna) have been observed in the damming, such that these dams normally designed and constructed without any fishways or fish ladders. Therefore, the dams mainly could (1) change aquatic ecosystems, (2) make limitation for downstream dispersal and blocking the upstream migration altogether, (3) periodically dried out downstream, (4) produce morphologically/genetically different populations in up and downstream and (5) affect the growth indices and reproductive characteristics, etc. Also, the introduction of non-native/invasion fishes into the reservoirs is an important threat for native fish communities. The diadromous species within the families Acipenseridae, Cyprinidae, Gobiidae, Petromyzontidae and Salmonidae were negatively affected by dams, whereas some native cyprinids and loaches those threatened by the drought were positively associated with the damming, where they could survive themselves in the reservoirs. It can be concluded that dams in Iran have negatively affected native – especially migratory – fish species by blocking their migration routes, whereas favouring non-native/invasion fish species, or altering existing aquatic habitats. Conservation programmes favouring native/endemic fishes in the constructed dams are strongly recommended, and fishways should be mandatory in the under construction/planned dams.

Made available in DSpace on 2020-12-12T02:17:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-09-01 Companhia Energética de São Paulo In a recent article, we described fitting electronic tags to the fish Prochilodus lineatus to document how a fishway connected aquatic habitats downstream and upstream of a major dam. Moreover, given that tagged fish remained upstream or downstream for periods extending months and years before returning to the fishway, and that observed patterns of passage were consistent with seasonal migratory cycles, and building on existing literature, we speculated that the fishway allows fish access to spawning habitats upstream and feeding habitats downstream. Our interpretation of the movement data resulted in several comments from Pelicice, Pompeu, and Agostinho (2020) and they outline various reasons by which, in their opinion, some of our conclusions may be mistaken. Their critique is threefold. First, they argue that the percentage of fish attracted into the fishway is too low to consider the fishway an effective link between the reservoir and the river downstream. We contend that without estimates of population size it is impossible to judge if 28% passage is “limited”; conceivably, the absolute number of fish passed may still be enough to maintain a viable population. Second, they assert that because receivers were located only in the fishway it is unknown if fish that used the fishway remained near the dam, or if they continued their migration. We counter with a brief literature review that documents P. lineatus migrating through reservoirs and spawning in tributaries. Third, they advocate for a broader conservation perspective and for additional research. We agree and, in the article, had already expressed this view that fishways are only a temporary fix and that we support their use only as an element of a broader environmental management package. We also agree with the need for more research but argue that procrastinating on conservation action may not be wise because we do not know if the research will be done, how long it will take, or what the cost may be of waiting. Sustainability Management Companhia Energética de São Paulo – CESP, SP-613 highway, km 78 Grupo de Pesquisa em Tecnologia em Ecohidráulica e Conservação de Recursos Pesqueiros e Hídricos – GETECH. Programa de Pós-graduação em Recursos Pesqueiros e Engenharia de Pesca Universidade Estadual do Oeste do Paraná – Unioeste Department of Hydraulics and Hydrology University of Valladolid U.S. Geological Survey Mississippi Cooperative Fish and Wildlife Research Unit Engineering College of Ilha Solteira Department of Biology and Zootechny Fish Ecology Laboratory Universidade Estadual Paulista – UNESP Engineering College of Ilha Solteira Department of Biology and Zootechny Fish Ecology Laboratory Universidade Estadual Paulista – UNESP

Managing intraspecific hybridization is crucial for maintaining a balance between inbreeding and outbreeding depression in winter and summer run steelhead (Oncorhynchus mykiss). While spatial distance is a common factor in maintaining reproductive isolation between these two ecotypes, physical barriers may also prevent hybridization, particularly in short river systems. To determine the effect of barriers and their removal on hybridization, we studied winter and summer steelhead populations in the Siletz River of northern coastal Oregon, which were historically separated by a physical barrier that was removed in the 1950s. We observed a large degree of admixture in the summer run population but little in the summer hatchery or wild winter populations, the former of which was established shortly after the removal of the barrier. This suggests that the high level of admixture in the wild summer run may be due to the removal of the barrier. We also found reduced genetic diversity in the wild summer run and in both hatchery populations. This highlights the need to balance inbreeding and outbreeding depression in hybridizing subpopulations.