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Downstream Movement (downstream + movement)
Selected AbstractsIllumination influences the ability of migrating juvenile salmonids to pass a submerged experimental weirECOLOGY OF FRESHWATER FISH, Issue 2 2009P. S. Kemp Abstract,,, The downstream migration of juvenile salmonids has previously been considered predominantly passive. It has been argued that passive displacement during periods of darkness is, partially at least, a result of an inability to maintain a fixed position in the absence of visual cues. In this study, behaviour of juvenile Pacific salmonids was assessed under conditions of light and dark as they passed through an artificial channel and encountered a submerged weir. Results indicated that when light, fish formed schools and actively explored the channel. Conversely, when dark (infrared illumination only) they did not form schools, but maintained randomly distributed positions holding station against the flow. As a consequence, more fish approached and either passed, or rejected, the weir when light. The majority of fish that passed the weir did so within the first minute of each trial. Fish predominantly passed through the channel facing downstream and changed orientation prior to passing tail first over the weir crest in the presence and absence of visual cues. The orientation switch was less common when dark. This study shows, at a fine-resolution scale, that downstream movement of juvenile salmonids can be inhibited as fish exhibit alternative behaviours in the absence of visual cues. Downstream movement was not predominantly passive. Fish passage design should not be based on the assumption that downstream migration is passive. [source] Migratory movements of pacu, Piaractus mesopotamicus, in the highly impounded Paraná RiverJOURNAL OF APPLIED ICHTHYOLOGY, Issue 6 2007M. C. Makrakis Summary 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. [source] Illumination influences the ability of migrating juvenile salmonids to pass a submerged experimental weirECOLOGY OF FRESHWATER FISH, Issue 2 2009P. S. Kemp Abstract,,, The downstream migration of juvenile salmonids has previously been considered predominantly passive. It has been argued that passive displacement during periods of darkness is, partially at least, a result of an inability to maintain a fixed position in the absence of visual cues. In this study, behaviour of juvenile Pacific salmonids was assessed under conditions of light and dark as they passed through an artificial channel and encountered a submerged weir. Results indicated that when light, fish formed schools and actively explored the channel. Conversely, when dark (infrared illumination only) they did not form schools, but maintained randomly distributed positions holding station against the flow. As a consequence, more fish approached and either passed, or rejected, the weir when light. The majority of fish that passed the weir did so within the first minute of each trial. Fish predominantly passed through the channel facing downstream and changed orientation prior to passing tail first over the weir crest in the presence and absence of visual cues. The orientation switch was less common when dark. This study shows, at a fine-resolution scale, that downstream movement of juvenile salmonids can be inhibited as fish exhibit alternative behaviours in the absence of visual cues. Downstream movement was not predominantly passive. Fish passage design should not be based on the assumption that downstream migration is passive. [source] The onset of downstream movement of juvenile Atlantic salmon, Salmo salar L., in a chalk streamFISHERIES MANAGEMENT & ECOLOGY, Issue 2 2002W. D. RILEY The downstream movements of wild Atlantic salmon, Salmo salar L., from their established feeding territories in the River Itchen, Hampshire, UK, were logged continuously over an 11-month period using a passive integrated transponder (PIT) antenna system. The time of these movements was then related to a number of monitored and calculated environmental parameters. Initial downstream movement of smolts in April was correlated with the onset of darkness, at which time salmon moved from their established feeding territories alone. No relationship was found between the number of smolts migrating and river flow or maximum daily water temperature. The timing of downstream movement of parr between October and March was random with regard to sunset and time of maximum daily water temperature, suggesting the environmental cue that initiates movement may be different outside the spring smolt period. [source] Water outflow as a cause of changes in trophic conditions for zooplanktivorous fish in reservoirsFISHERIES MANAGEMENT & ECOLOGY, Issue 1-2 2000L. Pehlivanov The seasonal changes and vertical distribution of zooplankton, the export of zooplankters by outflow through water management installations, and the feeding of zooplanktivorous fish were studied in two Bulgarian reservoirs. In a bottom-draining reservoir, planktonic crustacea >,1.0 mm were found to be selectively exported as a result of their diurnal vertical migrations. Increases in water outflow for irrigation resulted in a decrease in total zooplankton abundance, as well as changes in zooplankton size and species composition at the beginning of the summer. At the same time, major changes occurred in the feeding patterns of bleak, Alburnus alburnus (L.), and juvenile pikeperch, Stizostedion lucioperca (L.), the principal zooplanktivores in this reservoir. It is easy for bleak to switch to feeding on an alternative food, but a lack of available large prey organisms is suggested as the main cause of the downstream movement of pikeperch juveniles. In a surface-draining reservoir, the pattern of zooplankton export corresponded to those in natural lakes. Discharged water carried with it mainly small-sized epilimnetic zooplankton from the most numerous groups (i.e. rotifers, juvenile copepods and cladocerans) in the reservoir. Furthermore, outflow exports represent a relatively small part of total zooplankton number, and thus, do not disturb the natural zooplankton succession, and changes in abundance and composition Coincidental changes in the trophic responses for zooplanktivores (mainly juvenile cyprinids and percids) were not found. [source] Differences in endozoochorous dispersal between aquatic plant species, with reference to plant population persistence in riversFRESHWATER BIOLOGY, Issue 2 2005B. J. A. POLLUX Summary 1. In river ecosystems, populations are continuously subjected to unidirectional downstream currents resulting in a downstream movement of populations. To ensure long-term population persistence in rivers, organisms must have a mechanism for upstream dispersal, which allows them to re-colonise upstream areas. 2. In this study we assessed differences in the potential for endozoochorous seed dispersal of Sparganium emersum and Sagittaria sagittifolia, two aquatic plant species with different seed morphologies, by mallard (Anas platyrhynchos) and teal (Anas crecca), two duck species with different body weights. 3. We found no significant differences in seed retrieval (the proportion of ingested seeds retrieved after gut passage) and seed retention time (time between seed ingestion and retrieval), between mallard and teal, despite the difference in body weights. We did find a significantly higher germination (%) over retention time of S. emersum seeds retrieved from teal compared with mallard, most likely related to a more efficient removal of the seed coat during passage through the gut of teal. 4. There were large differences between S. emersum versus S. sagittifolia in: (i) seed retrieval (22.65 ± 20.8% versus 1.60 ± 2.4%, respectively); (ii) seed retention time in duck gut, with a maximum of 60 h versus 12 h; (iii) the effect of gut passage on seed germination, with an increase of approximately 35% versus a decrease of 25%; and (iv) the effect of gut passage on seed germination rate, with an acceleration of 10 days versus a delay of 3 days on average. The results show that S. emersum has a higher potential for endozoochorous dispersal by ducks and postdispersal establishment than S. sagittifolia. 5. We propose that, in rivers, bird-mediated seed dispersal may promote re-colonisation of upstream areas, enabling long-term plant population persistence. [source] Detection efficiency of multiplexed Passive Integrated Transponder antennas is influenced by environmental conditions and fish swimming behaviourECOLOGY OF FRESHWATER FISH, Issue 4 2009J. C. Aymes Abstract,,, The efficiency of a Passive Integrated Transponder (PIT)-tag detection system was tested during a 23-day experiment using a permanent digital video to record the passage of fish through multiplexed antennas. Coupling video to the PIT system allowed the detection of error sources and the correction of erroneous data. The efficiency of the detection system and its variation were investigated according to fish swimming speed, direction of movement and individual fish behaviour. Influence of time and environmental conditions on detection results were also checked. The PIT tag system was 96.7% efficient in detecting fish. Upstream movements were better detected (99.8%) than downstream movements (93.7%). Moreover, results showed that efficiency rate was not stable over the experiment; it was reduced on stormy days. Several sources of errors were identified such as sub-optimal orientation of the PIT tag relative to the antenna plane, the influence of fish swimming speed, individual fish behaviour and influence of environmental conditions. [source] Dispersal in drift-prone macroinvertebrates: a case for density-independenceFRESHWATER BIOLOGY, Issue 5 2002S. HUMPHRIES 1.,Studies of dispersal of macroinvertebrates in streams and rivers tend to be focused on drift, whilst benthic movements are usually considered to be less important. 2.,Field-enclosure experiments with the mayfly Baetis rhodani indicate that net dispersal in this species is simply a proportional loss of individuals from the benthos. 3.,Neither net upstream or downstream movements exhibited evidence of density-dependence in the form of curvilinear relationships between initial and final densities. 4.,The net number of animals moving upstream did not differ significantly from the net number moving downstream. 5.,The probable mechanisms behind density-independent dispersal are discussed, as are the implications for our understanding of population dynamics in relation to invertebrate drift. [source] Migratory movements of pacu, Piaractus mesopotamicus, in the highly impounded Paraná RiverJOURNAL OF APPLIED ICHTHYOLOGY, Issue 6 2007M. C. Makrakis Summary 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. [source] Long-distance downstream movements by homing adult chinook salmonJOURNAL OF FISH BIOLOGY, Issue 3 2006M. L. Keefer Unusually long downstream movements totalling several hundred kilometres to >1100 km were observed during upstream homing migrations of radio-tagged spring chinook salmon Oncorhynchus tshawytscha in the Columbia and Snake Rivers, U.S.A. Downstream migrants, identified by their repeated ascension and fallback over a series of large hydroelectric dams within the migration corridor, were primarily hatchery-origin males. [source] | |||||||||||||