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1.
The aim of this study was to assess escapement success of silver eels, Anguilla anguilla (L.), in a lowland river while passing a reservoir and a hydropower station. It was hypothesized that passage success would be lowest at the hydropower station and that survival and migration speed would be highest in the free‐flowing river section upstream the reservoir. Forty‐five female silver eels 56–86 cm in length were tagged with acoustic transmitters and released in November 2006. Their migration was monitored via automatic listening stations (ALS) in various sections of the river, covering a total migration distance of 64 km. Survival and progression rate of downstream migration was highest in the upstream river section and significantly lower in the reservoir. The eels apparently had trouble finding their way past the turbines and spent between 1.5 and 35 h in the forebay. The results show that within the study period, only 23% of the tagged eels reached the tidal limit, mainly due to difficulties in passing the hydropower dam. With such high loss‐rates, the escapement goals set in the management plan cannot be achieved.  相似文献   

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Escapement success and migration patterns of silver eels Anguilla anguilla (L.) was studied by acoustic telemetry in three natural free‐flowing and one dammed river and in Curonian Lagoon in Lithuania. Mean downstream migration speed and escapement success were almost the same in the shorter 210 km dammed river (52%, 13.6 km/day) and the considerably longer 300–480 km free‐flowing rivers (53%, 10.7 km/day). Despite the similarity between migration speed in the Curonian Lagoon (14.6 km/day) to that in rivers, migration success was significantly higher (71%) in the Lagoon. Although a majority of silver eels in Lithuania start migrating downstream in spring, the peak of eel migration into the Baltic Sea was observed during late fall. Overall migration success in the rivers and the Lagoon was 35%. Relatively low escapement may have negative consequences on the success on eel stock restoration and must be addressed when strategically planning for the production of spawners.  相似文献   

5.
The global population of European eel (Anguilla anguilla) is rapidly declining, and migration barriers in rivers are believed to be one of several key causes. While progress has been made in the development of bypass solutions, they are often constructed based on a limited knowledge of swimming behaviour. A bypass close to the stream bed is often recommended at fish passage facilities to accommodate downstream eel migration. The results of this recommendation are poorly studied, and the few studies that exist show varying bypass efficiencies. The current study used acoustic telemetry with depth sensors to explore the three-dimensional migratory behaviour of downstream-migrating silver eels. The eels were tracked as they approached a hydropower plant with a state-of-the-art angled bar rack and full-depth bypass. Downstream and upstream swimming differed in preferred vertical and lateral positions. During periods of local downstream movement, the density of observations was largest in the upper middle section, away from the river boundaries and in higher velocities. Conversely, when moving upstream, eels tended to avoid the upper layers of the middle part of the river, swimming closer to the riverbed and using the bank areas to a greater extent. Downstream-moving fish swam higher in the water column during night and in turbid conditions (high discharge). When approaching the impassable bar rack and the full-depth bypass, the eels searched most intensely but not exclusively along the bottom third of the rack, often exploring at new depths after changing direction. The impediment passage efficiency was 100% when both bypass solutions were considered. The study provides knowledge of the swimming behaviour of silver eels, which is relevant for the design of bypass solutions for eels at migration barriers.  相似文献   

6.
We present the magnitude of losses of European eel Anguilla anguilla and American eel A. rostrata in passage through propeller and Francis turbines at hydroelectric projects. Survival and injury rates and types were turbine type related. Overall, eel survival was higher (mean ± 90% CI = 95.1 ± 5.3%,) and injury rate lower (12.5 ± 10.5) at Francis than propeller turbines (survival = 80.7 ± 6.4%; injury rate = 25.7 ± 7.9%). The common injury type at Francis turbines was bruises and at propeller turbines was severance. Blade shape and thickness of the leading edge of the blades (rounded, thick buckets of Francis turbines v. flatter, sharper edged blades in propeller turbines); eel entry routes into the turbines; their flexible, cylindrical body shape and orientation probably contributed to these differences. Relationship between survival and injury and turbine characteristics was turbine specific. For Francis turbines, one negative correlation (r = −0.986, P < 0.01) between survival and runner speed was found and two positive correlations between injury rates and fish length (r = 0.740, P < 0.10) and number of blades (r = 0.835, P < 0.05) were noted for propeller turbines. Several severely injured eels remained active 48 h after turbine passage suggesting caution is warranted when using telemetric movement for estimating eel survival. We conclude there is a need to (a) better understand travel paths and approach orientation of eels through turbines; (b) determine where only eel passage is of concern at hydropower plants that have both turbine types and therefore preferential operation of Francis turbines may be considered; (c) inform hydropower plant operators where turbine replacement is being considered and downstream eel passage is of concern that replacement by Francis or bulb turbines may prove beneficial for eel passage.  相似文献   

7.
In 2002 and 2003, the Bishops Falls hydroelectric generating facility on the Exploits River, insular Newfoundland, Canada, underwent extensive refurbishing including replacement of turbines and installation of a ‘retrofitted’ bypass and fish handling system. The effectiveness of this new bypass system has been assessed during the annual downstream run of wild Atlantic salmon smolt and kelt in 2003 and 2004. In 2003, 195 smolt were radio tagged and released between June 9 and July 2, in the forebay of the hydro plant (19 releases) and one upstream (in-river) release. Fish guidance efficiency (FGE) of the system overall was 63% (123 of 195 fish) with 36 fish passing through the turbines, and six known mortalities. In 2004, between June 9 and July 2, a total of 358 smolt and 103 kelt were released in the forebay in 45 and 13 releases (n = 8 per release), respectively. The FGE of the system for smolt was 71.7% (257 of 358 fish) and for kelt was 92.3% (95 of 103 fish). In 2004, 96 tagged smolt passed through the turbines and 43 (44.8%) were detected at a downstream station confirming they had survived turbine passage, suggesting an overall survival of smolt passage of the Bishops Falls hydro facility in the order of 85%. A total of seven kelts (6.8%) passed through the turbines and were not detected 1.5 km downstream suggesting they did not survive turbine passage. Smolt spent on average 39.8 h in the forebay before exiting in 2003 and forebay residency averaged 26 h in 2004. In both years, most smolt selected their passage route, actively or passively, within the first 10 h with secondary peaks at 25–30 h and 50–55 h, corresponding to evening passage in the second and third night, after release. Few smolt were bypassed or entrained into turbines during daylight hours. In both years turbine passed smolt spent more time in the forebay suggesting the longer fish reside in the forebay the greater the likelihood of turbine entrainment. Kelt were either bypassed or turbine entrained relatively quickly, within 2 h of release, and virtually all kelts were bypassed/turbine entrained during the hours of 18:00 and 01:00. These data on fish behaviour and residency in the forebay will assist further refinement of operations of the bypass facility to optimize survival.  相似文献   

8.
Downstream migrations and population characteristics of eels Anguilla anguilla were studied between 1967–1982 and 2002–2005 using a fish trap and electrofishing in the Girnock Burn, a small oligotrophic upland sub‐catchment of the River Dee, north‐east Scotland, 70 km from the tidal limit. In limited mark‐recapture studies, 9% of eels were recaptured up to three times and 97% of all recaptures were made at the same electrofishing site. The recaptured eels had a low mean growth rate of c. 13 mm year−1. Smaller eels appeared to show preferences for shallower habitats with small boulder and gravel–sand substrata. Trap catches exhibited seasonal modes in total length at 140–180 mm in late spring, and 320–340 mm in early autumn, probably relating to water temperatures and discharges. From other studies, it is inferred that the spring mode comprised sexually undifferentiated nomadic eels and the autumn mode differentiated males beginning their spawning migration. Large female eels were rare. The fish trap appears to have formed a major barrier to upstream migration since its construction in 1966. In‐stream density has decreased significantly since then from 16 to three eels 100 m−2, biomass from 260 to 78 g 100 m−2 and emigrants from 700 to 100 individuals year−1. Emigrants have comprised c. 5% of the standing stock year−1 since the 1970s. The proportion of larger differentiated eels in the Girnock Burn has, however, remained relatively constant and escapement has been c. 100–200 (probably male) eels year−1 since the late 1960s. Evidence, including that from other northerly British rivers, is reviewed to assess the possible impacts of Europe‐wide declines in glass eel recruitment since the 1980s. It is recommended that the data series be maintained, plus further sex determination and ageing studies. Installation of an upstream trap to capture immigrants and studies of recolonization are proposed.  相似文献   

9.
Vital statistics such as growth, mortality, and maturity parameters are crucial in understanding the population dynamics of a species. A total of 7 074 Japanese eels (Anguilla japonica) in the lower reach of the Kao‐Ping River, southern Taiwan, were collected with eel tubes in 1998 ~ 2004 and shrimp nets in 2004 ~ 2007. Data from 2004 were excluded due to mixed gear information and escapement of cultured eels; in subsequent years escaped cultured eels were identified and excluded from analyses. The estimated asymptotic length in the von Bertalanffy growth function (84.5–110 cm) was smaller, while the Brody growth parameter (0.30–0.44 year?1) was higher using electronic length frequency analysis (ELEFAN) than when using Shepherd’s length composition analysis (SLCA). The total instantaneous mortality rate (Z) was around 1 for periods 1998–2003 and 2 year?1 for 2005–2007 using length‐converted catch curves. The 95% confidence intervals of Z did not overlap for two of the periods, suggesting that the mortality rates were significantly higher during 2005–2007, possibly due to the introduction of shrimp nets. The maturity function differed significantly between sexes, indicating that females become silver eels at a larger size. The Japanese eels in the lower reach of the Kao‐Ping River were likely heavily exploited, thus management and conservation actions are strongly recommended.  相似文献   

10.
Tracking 47 post-spawned adult Atlantic salmon Salmo salar L. in a hydropower-regulated river through autumn, winter and spring revealed that winter survival was 56% and 75% in two study years, respectively, with higher mortality of males than females (50% vs. 33% and 100% vs. 13%, respectively). Some kelts (n = 7) displayed nondirected movements that were interpreted as a reconditioning period for an average of 9–17 days prior to directed downstream movements indicating the initiation of migration. Survival after the initiation of migration in spring was 83% and 94% to the hydropower dam in the first and second study years, and decreased to 60 and 63%, respectively, after dam passage. There were no further losses in the downriver reach in the second year, with the first year having a cumulative survival estimate of 53% to the river mouth. Kelts approached the dam when the spillway gates were available as a passage option most of the time (64%–75%), but some kelts arrived at the dam or had not yet passed when spillways were closed (n = 6) and the only remaining passage option was restricted to the turbines. However, all but one kelt that must have passed via turbine were successful in reaching the river mouth. Migratory delay presumably due to searching behaviour caused by low water flow was estimated at approximately 6 days as migration rates were significantly slower in the reservoir (median ± s.e. 8.5 ± 2.5 km day−1) than up- (29.7 ± 5.0 km day−1) or downriver (22.1 ± 3.1 km day−1). The proportion of time (median 30%) that kelts spent swimming upstream (searching behaviour) in the reservoir was a significant variable for migration success.  相似文献   

11.
A method was developed to quantify the number and biomass of European eels Anguilla anguilla escaping to the ocean for breeding. The non‐intrusive method, involving a fixed‐position, high‐frequency multi‐beam sonar, permitted constant surveillance of A. anguilla movements throughout their 5 month escapement season (July to December). During this period, >1000 individuals were monitored escaping to the Atlantic Ocean from their freshwater habitat in the River Huntspill study site (Somerset, U.K.). The total length of each fish was measured using the sonar software. These measurements were then converted to an estimate of mass using a length:mass regression relationship derived from historical fyke‐net data from this site, comprising c. 500 A. anguilla length:mass measurements collected over a 10 year period. The net biomass of escapement from the study site was equivalent to c. 6 kg ha?1 year?1, lower than the present European target which would require at least 7 kg ha?1 year?1 from this habitat. These findings demonstrate the capabilities of this monitoring technique and its usefulness both as a tool to assess the compliance with conservation targets and as a tool to evaluate the success of conservation measures for elusive aquatic species such as A. anguilla.  相似文献   

12.
Downstream migration of Anguilla anguilla silver eels was studied in the Lower Rhine, Germany, and the Rhine Delta, The Netherlands, in 2004–2006. Fish ( n = 457) released near Cologne with implanted transponders were tracked by remote telemetry at 12 fixed detection locations distributed along the different possible migration routes to the North Sea. Relatively more A. anguilla migrated via the Waal than the Nederrijn, as would be expected from the ratio of river discharges at the bifurcation point at Pannerden. Downstream migration from the release site to Rhine-Xanten, close to the German–Dutch border, generally occurred in the autumn of the year of release but migration speeds tended to be low and variable and unaffected by maturation status or river discharge rates. Detection frequencies were not significantly related to discharge peaks or lunar cycles, but there was a minor detection peak 1–6 h after sunset. Between 2004 and 2009, 43% of the 457 A. anguilla released were never detected and of the 260 detected entering the Netherlands, 83 (32%) were detected escaping to the sea, 78 (94%) via the Nieuwe Waterweg and three (4%) and two (2%) via the sluices in the Haringvlietdam and Afsluitdijk, respectively. Possible causes of non-detections are discussed and it is suggested that many A. anguilla temporarily ceased migration, but that fishing mortality could have been important during passage through the Dutch parts of the Rhine. Practical implications of the results for predicting emigration routes, timings and magnitudes and use in management initiatives to promote escapement of A. anguilla silver eels to the sea are critically discussed.  相似文献   

13.
American Eel Anguilla rostrata abundance has declined in recent decades, in part because sexually maturing, silver-stage adults, outmigrating from freshwater to oceanic spawning grounds, encounter migratory blockades or perish when passing through active hydroelectric turbines. To help improve downstream passage effectiveness and increase survival rates, the role of silver-stage American Eel conspecific chemical cueing during outmigration was investigated using a new type of bioassay. Inside a laboratory flume, downstream-swimming eels were exposed to both live (putative attractant) and dead (putative repellent) conspecific washings to determine whether their trajectory of downstream movement, level of activity, or time spent inside targeted areas of the arena changed after exposure. Silver eels were not attracted to or repulsed by either odor, as none of five scoring metrics indicated a behavioral response. Results did not support the hypothesis that conspecific chemical cueing is a mechanism for downstream migration coordination or danger avoidance; however responses may not have been readily apparent in this type of assay. Fisheries managers may opt to focus future research on more feasible restoration efforts using alternate experimental designs to remedy this ecological issue.  相似文献   

14.
This study monitored post-release movements of 20 wild Japanese eels (Anguilla japonica) [mean ± S.D. 520.8 ± 92.3 mm total length (TL), 217.9 ± 146.3 g body mass (BM)] in a brackish water lagoon in northeastern Japan using acoustic telemetry to elucidate how wild Japanese eels use different river, estuary and marine environments. In addition, 12 cultured Japanese eels (TL = 578.9 ± 18.0 mm, BM = 344.9 ± 25.5 g) were released to understand the comparative behaviours of wild and cultured eels. Both types of eels were simultaneously released in the southern inner part of the lagoon in September 2016 where there are freshwater influences from a river. Following release, eight of the wild eels (40%) were largely sedentary near the released point (river mouth) and stayed at the site for overwinter. Nonetheless, several individuals showed behavioural plasticity of habitat use: three wild eels moved towards the northern part of the lagoon with stronger influence from the sea during May–July 2017. Two wild eels showed clear repeated movements from the lagoon to a river at night and returned to the lagoon by dawn for more than a week every day, and one wild eel migrated upstream for overwintering. Signals from 55% of the wild eels could be detected for more than 6 months, whereas those from all of the cultured eels were lost by December 2016, indicating a short resident time of large cultured eels (BM > 200 g) released in a brackish water area. One wild silver eel migrated to the outer sea during the ebb tide at night in November 2016, probably triggered by the decrease in water temperature (from c. 20°C to c. 13°C), and seven cultured eels similarly moved to the outer sea during October–November 2016. The results revealed the similarities (e.g., nocturnal movements) and differences (e.g., stay period and seasonal movements) in the behavioural characteristics of wild and cultured eels and indicated that habitat connectivity among river, estuary and coastal waters is crucial for enabling eels to efficiently utilise these productive habitats through their behavioural plasticity.  相似文献   

15.
This study demonstrates passage of age‐0+ year individuals of pikeperch Sander lucioperca, common bream Abramis brama and non‐native tubenose goby Proterorhinus semilunaris from the Nové Mlýny Reservoir into the River Dyje (Danube River basin, Czech Republic) through the turbine of a hydropower facility. Most fishes had standard length (LS) in the range 12–33 mm. Seasonal patterns corresponded with spawning activity, i.e. an early single spawning event for S. lucioperca, multiple spawning events for A. brama and continuous spawning with a later start and prolonged duration for P. semilunaris. Sander lucioperca, P. semilunaris and larger A. brama (>22 mm) drifted almost exclusively during the dark; smaller A. brama displayed no preference for light or dark. Proterorhinus semilunaris displayed significantly lower mortality than other species when passing through the turbine (3% compared to 18%). The passage of high numbers of P. semilunaris from the reservoir (estimated at 473 000 individuals per year), and their subsequent mass downstream drift, may have contributed to rapid population establishment along the River Dyje and the quick downstream expansion.  相似文献   

16.
The aim of this 2008–2012 study was to prove the hypothesis that the Three Gorges Reservoir (TGR) and the upper free‐flowing section can offer a habitat for restocking the Chinese sturgeon, Acipenser sinensis. Thus, 498 cultured A. sinensis (including 28 sub‐adults tagged with ultrasonic transmitters) were released into the TGR and the adjacent free‐flowing section of the Yangtze River. The distribution, movement and growth of the released fish were collected by acoustic telemetry and bycatch information. Results indicated that only three sub‐adults migrated upstream to the free‐flowing section where they remained for the three‐year observation (limited by the longevity of the transmitter battery). However, most sub‐adults migrated downstream after release, with a migration distance of 15–877 km as well as a tracking duration from 19 to 6063 h. The downstream traveling speed in the free‐flowing section (mean = 3.70 km h?1, range = 1.51 – 8.25 km h?1) was significantly faster than that in the reservoir section (mean = 1.05 km h?1, range = 0.12 – 1.82 km h?1; p < 0.05). Only three sub‐adults migrated to within 3 km of Three Gorges Dam (TGD) and stayed in the reservoir. Sub‐adults stayed obviously deeper within the reservoir (mean = 11.47 m) than in the free‐flowing section (mean = 3.63 m; p < 0.05). Juveniles were recaptured from 45 – 810 km downstream their release sites with a mean traveling speed of 1.05 km h?1 (range = 0.13 – 1.82 km h?1), lower than that of the sub‐adults released in the free‐flowing section. Twelve percent of juveniles released in one of the tributaries of the Yangtze River found the entrance and migrated downstream to the reservoir within the first 30 days. Average body weight of the recaptured juveniles increased by 10.3% (range = 2.3% – 15.3%) and some crustaceans (e.g. river shrimp) were found in the stomach and gut of two juveniles. The results demonstrate that the TGR and its adjacent upstream free‐flowing Yangtze River section can serve as reintroduction sites to support a certain quantity of Chinese sturgeon to remain and mature there.  相似文献   

17.
An extant stock of wild pallid sturgeon Scaphirhynchus albus persists in the fragmented upper Missouri River basin of Montana and North Dakota. Although successful spawning and hatch of embryos has been verified, long‐term catch records suggest that recruitment has not occurred for several decades as the extant stock lacks juvenile size classes and is comprised exclusively of large, presumably old individuals. Ages of 11 deceased (death years 1997–2007) wild S. albus (136–166 cm fork length) were estimated based on pectoral fin spines, sagittal otoliths and bomb radiocarbon (14C) assays of otoliths to test the hypothesis that members of this stock are old and to provide inferences on recruitment years that produced the extant stock. Age estimations based on counts of presumed annuli were about 2 years greater for otoliths (mean = 51 years, range = 43–57 years) than spines (mean = 49 years, range = 37–59 years). Based on 14C assays, confirmed birth years for all individuals occurred prior to 1957, thus establishing known longevity of at least 50 years. Estimated age based on presumed otolith annuli for one S. albus was validated to at least age 49. Although 14C assays confirmed pre‐1957 birth years for all S. albus, only 56% of estimated ages from spines and 91% of estimated ages from otoliths depicted pre‐1957 birth years. Both ageing structures were subject to under‐ageing error (up to 15 years). Lack of or severe curtailment of S. albus recruitment in the upper Missouri River basin since the mid‐1950s closely parallels the 1953–1957 timeframe when a mainstem reservoir was constructed and started to fill. This reservoir may function as a system‐wide stressor to diminish recruitment success of S. albus in the upper Missouri River basin.  相似文献   

18.
A mark‐recapture study was conducted in 1997–2005 to investigate movements of stocked pacu, Piaractus mesopotamicus, in the Paraná River Basin of Brazil, Paraguay, and Argentina. Fish raised in cages within the Itaipu Reservoir and in ponds were tagged externally (n = 2976) and released in the Itaipu Reservoir (53.2%) and bays of its major tributaries (46.8%). In total, 367 fish (12.3%) were recaptured. In all, 91% of the pacu moved away from the release site; upstream movements were more extensive than downstream movements. Pacu traveled upstream a maximum of 422 km (average of 41.3 km) at a maximum rate of 26.4 km day−1 (av. 0.8). Downstream movements were limited in terms of number of individuals and distance moved. Fish released during the wet season moved farther than those released during the dry season, and feeding rather than spawning might have been the compelling reason for movement. Although fish passed downstream through dams, none of the marked fish were detected to have moved upstream through the passage facilities. Pacu showed movement patterns not radically different from those of other neotropical migratory species, but their migratory movements may not be as extensive as those of other large migratory species in the basin.  相似文献   

19.
The density, size and age distribution were investigated for 233 eels, Anguilla japonica, sampled in fresh and brackish water areas of the Kojima Bay-Asahi River system, Okayama, Japan, to evaluate the possible patterns of dispersal of eels that recruit to this area. Migratory histories of 183 eels were categorized into 5 types depending on the Sr and Ca concentrations in their otoliths: (1) brackish water residents (74 fish, 40.4%), which settled in saline water and remained until capture; (2) freshwater residents (46 fish, 25.1%), which settled in freshwater and remained until capture; (3) upstream shifters (3 fish, 1.6%), which settled in saline water and moved upstream into freshwater; (4) downstream shifters (53 fish, 29.0%), which settled in freshwater and moved downstream into saline water; (5) multiple habitat shifters (7 fish, 3.8%), which shifted their habitats between freshwater and saline water more than twice. For eels captured in the brackish water area, fish density decreased with distance in the downstream direction, while the size and age of eels increased. For eels captured in the freshwater area, size and age were greater than those in the upper-most brackish site. These observations suggest that eels in this system initially accumulate in the lower reaches of the river and then disperse in both upstream and downstream directions following their growth.  相似文献   

20.
Otolith stable‐oxygen‐isotope composition and microstructure were analysed in order to investigate the vertical habitat shift of deep‐sea cusk eels (Ophidiiformes). Otolith δ18O profiles suggested that both viviparous blind cusk eels and oviparous cusk eels experienced a pelagic larval stage and then settled to the deep‐sea floor over a vertical distance that ranged among individuals from 200 to >1000 m. This result shows that the larvae of viviparous Barathronus maculatus undertake an ontogenetic vertical migration after a period of larval drift that may facilitate their wide distribution on the sea floor.  相似文献   

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