Upstream migration by young pigmented freshwater eels (Anguilla australis australis Richardson) in Tasmania

1984 ◽  
Vol 35 (1) ◽  
pp. 61 ◽  
Author(s):  
RD Sloane
Keyword(s):  
Water Temperature ◽  
Fresh Water ◽  
River Flow ◽  
Late Spring ◽  
Day Length ◽  
Upstream Migration ◽  
Single Specimen ◽  
Anguilla Australis ◽  
And Control ◽  
Freshwater Eels

During late spring and summer, upstream migrations by young pigmented freshwater eels (elvers) can be seen at stream barriers in Tasmania. The elver runs at two major hydro-electric dams, Trevallyn and Meadowbank, were sampled regularly during the period 1977-1981 and migrations at a number of smaller stream barriers throughout Tasmania were also investigated. Migrating elvers were found to be short-finned eels, A. a. australis; only a single specimen of the long-finned eel, A. reinhardii Steindachner, was recorded. Elvers sampled at inland stream barriers were both larger and older than those found nearer the sea, indicating that eels migrate farther upstream for several years in succession. Eels involved in upstream migration were found to be shorter than 25 cm, having spent up to 10 years in fresh water. Day length, water temperature and river flow may all contribute to the initiation and control of elver migrations. The numbers of elvers involved in annual migrations at major hydro- electric dams in Tasmania are substantial: the largest migration occurs at Trevallyn, where between 3 × 106 and 5 × 106 elvers take part each year. These elvers represent a considerable stocking poterltial and could be used to expand the local wild-eel fishery.

Preliminary observations of migrating adult freshwater eels (Anguilla australis australis Richardson) in Tasmania

1984 ◽  
Vol 35 (4) ◽  
pp. 471 ◽  
Author(s):  
RD Sloane
Keyword(s):  
Water Temperature ◽  
Significant Positive Correlation ◽  
River Flow ◽  
Downstream Migration ◽  
Single Male ◽  
Male Specimen ◽  
Anguilla Australis ◽  
Daily Water Temperature ◽  
Daily Water ◽  
Freshwater Eels

The downstream migration of maturing adult short-finned eels, A. a. australis, was recorded at an eel trap on the Clyde River during the 1981-1982 season. 5.2 t of eels entered the trap from November to April with 53% of the catch taken during January. Of the 190 eels examined, only a single male specimen was found. Female A. a. australis migrated downstream at a mean length of 94.5 cm, a mean weight of 1700 g and a mean age of 22.1 years (range 18-30 years). There was a significant positive correlation between catch and water temperature, temperatures above 12�C being associated with eel migration. The peak catch occurred during January and coincided with the highest record of mean daily water temperature (20.5�C). The migration did not appear to be influenced by moon phase, and river flow was controlled.

Invasion and upstream migration by glass-eels of Anguilla australis australis Richardson and A. reinhardtii Steindachner in Tasmanian Freshwater Streams

1984 ◽  
Vol 35 (1) ◽  
pp. 47 ◽  
Author(s):  
RD Sloane
Keyword(s):  
Fresh Water ◽  
River Flow ◽  
Condition Factor ◽  
Late Summer ◽  
Upstream Migration ◽  
Larval Life ◽  
Freshwater Streams ◽  
Anguilla Australis ◽  
Glass Eels ◽  
High River Flow

The recruitment of glass-eels into fresh water was investigated by hand-netting and electrofishing at the lowest permanent freshwater riffle on several streams in eastern Tasmania. Measurements of the forward extent of the dorsal fin distinguished the short-finned eel, A. a. australis, from the long-finned eel, A. reinhardtii; this separation was verified by vertebral counts and A. a, australis glass-eels were found to be larger than A. reinhardtii. A. a. australis glass-eels were collected at the first riffle during all seasons of the year except mid-summer. Numbers in the catch declined during mid-winter, probably as a result of an effective seaward movement of the freshwater-estuarine interface during periods of high river flow; A. a. australis glass-eels were still found to be abundant near estuary mouths at such times. A. reinhardtii glass-eels exhibited a more restricted movement into fresh water during late summer and autumn with no collections recorded after mid-winter. For both species, the stage of pigmentation was found to advance as the season progressed, and length, weight and condition factor declined with advancing pigmentation. The otoliths of invading glass-eels of both species appeared similar with a single summer ring, suggesting a larval life of 1-1½ years. The restricted invasion period of A. reinhardtii and the similar size throughout the species range suggests a short and precise larval life. The length of larval life of A. a. australis is probably quite variable, resulting in a more substantial and prolonged influx of glass-eels into Tasmanian waters.

scholarly journals Aspects of the Biology of Juvenile Freshwater Eels (Anguillidae) in New Zealand

2021 ◽  
Author(s):  
◽  
Donald John Jellyman
Keyword(s):  
New Zealand ◽  
Fresh Water ◽  
Habitat Preferences ◽  
Spring Tide ◽  
Age Groups ◽  
Upstream Migration ◽  
Coastal Lake ◽  
Anguilla Australis ◽  
Glass Eels ◽  
Freshwater Eels

<p>The early freshwater life of the two species of New Zealand freshwater eels, Anguilla australis schmidtii Phillipps and A. dieffenbachii Gray was studied involving an examination of 8131 glass-eels, 5275 migratory elvers, and 4291 resident eels of less than 26 cm. Most eels were collected from the Makara Stream, Wellington by set-net, hand-net and electric fishing. These extensive samples together with subsidiary collections from elsewhere in New Zealand show that glass-eels of both species arrive in fresh-water from July to December. Their otoliths indicate a marine larval life of about 18 months but it is not possible as yet to locate the precise oceanic spawning areas. Migratory movements of glass-eels are in two phases: an invasion of fresh-water from the sea and an upstream migration. The former occurs only at night with a periodicity corresponding to the daily ebb-flood tidal rhythms. There is a seasonal reversal in this response which is attributable to the onset of the behavioural transition taking place prior to the second migratory phase. Increased pigmentation and changes in response to light, flowing fresh-water and schooling tendencies characterise this latter migration which occurs primarily at spring tide periods. Such juvenile eels show specific habitat preferences and a high degree of olfactory differentiation of water types. This behaviour, together with pigment development and physical tolerances, was studied in the laboratory. Measurements of invading glass-eels show that mean length, weight and condition all decline throughout the season of arrival but mean vertebral numbers remain constant. An upstream migration of small eels (elvers) occurs each summer and is readily observed at many hydro-electric stations. These migrations, comprising eels of mixed sizes and age groups, penetrate progressively further upstream each year. In both species, scales begin formation at body lengths of 16.5-20 cm. All features of scale formation, including the number of scale rings, are related to length with relative differences in rate of development occurring between the species. In contrast to scale rings, otolith rings are annual in formation and become visible after grinding or burning the otolith. Growth rates established for 273 eels to 29 cm in length from the Makara Stream, Wellington, are slow, with mean annual increments of 2.2 and 2.1 cm respectively for shortfins and longfins. In contrast, shortfins from a coastal lake near Wellington reach 26 cm in their third year of freshwater life. Length-weight relationships for small eels are given together with mean monthly condition factors. Growth studies on elvers held in a multiple tank unit in which temperature, density, and amount and frequency of feeding could be controlled, show that young eels grow more slowly than normal under such conditions. However, growth appears optimum at 20 degrees C with a feeding rate of 5-7% body weight per day. Feeding efficiency decreases with higher temperatures. At both glass-eel and elver stages, shortfins adapt and survive better under artificial conditions.</p>

scholarly journals Aspects of the Biology of Juvenile Freshwater Eels (Anguillidae) in New Zealand

2021 ◽  
Author(s):  
◽  
Donald John Jellyman
Keyword(s):  
New Zealand ◽  
Fresh Water ◽  
Habitat Preferences ◽  
Spring Tide ◽  
Age Groups ◽  
Upstream Migration ◽  
Coastal Lake ◽  
Anguilla Australis ◽  
Glass Eels ◽  
Freshwater Eels

<p>The early freshwater life of the two species of New Zealand freshwater eels, Anguilla australis schmidtii Phillipps and A. dieffenbachii Gray was studied involving an examination of 8131 glass-eels, 5275 migratory elvers, and 4291 resident eels of less than 26 cm. Most eels were collected from the Makara Stream, Wellington by set-net, hand-net and electric fishing. These extensive samples together with subsidiary collections from elsewhere in New Zealand show that glass-eels of both species arrive in fresh-water from July to December. Their otoliths indicate a marine larval life of about 18 months but it is not possible as yet to locate the precise oceanic spawning areas. Migratory movements of glass-eels are in two phases: an invasion of fresh-water from the sea and an upstream migration. The former occurs only at night with a periodicity corresponding to the daily ebb-flood tidal rhythms. There is a seasonal reversal in this response which is attributable to the onset of the behavioural transition taking place prior to the second migratory phase. Increased pigmentation and changes in response to light, flowing fresh-water and schooling tendencies characterise this latter migration which occurs primarily at spring tide periods. Such juvenile eels show specific habitat preferences and a high degree of olfactory differentiation of water types. This behaviour, together with pigment development and physical tolerances, was studied in the laboratory. Measurements of invading glass-eels show that mean length, weight and condition all decline throughout the season of arrival but mean vertebral numbers remain constant. An upstream migration of small eels (elvers) occurs each summer and is readily observed at many hydro-electric stations. These migrations, comprising eels of mixed sizes and age groups, penetrate progressively further upstream each year. In both species, scales begin formation at body lengths of 16.5-20 cm. All features of scale formation, including the number of scale rings, are related to length with relative differences in rate of development occurring between the species. In contrast to scale rings, otolith rings are annual in formation and become visible after grinding or burning the otolith. Growth rates established for 273 eels to 29 cm in length from the Makara Stream, Wellington, are slow, with mean annual increments of 2.2 and 2.1 cm respectively for shortfins and longfins. In contrast, shortfins from a coastal lake near Wellington reach 26 cm in their third year of freshwater life. Length-weight relationships for small eels are given together with mean monthly condition factors. Growth studies on elvers held in a multiple tank unit in which temperature, density, and amount and frequency of feeding could be controlled, show that young eels grow more slowly than normal under such conditions. However, growth appears optimum at 20 degrees C with a feeding rate of 5-7% body weight per day. Feeding efficiency decreases with higher temperatures. At both glass-eel and elver stages, shortfins adapt and survive better under artificial conditions.</p>

scholarly journals Decreased stock entering the Belgian Meuse is associated with the loss of colonisation behaviour in yellow-phase European eels

2018 ◽  
Vol 31 ◽  
pp. 7 ◽  
Author(s):  
Billy Nzau Matondo ◽  
Michaël Ovidio
Keyword(s):  
Home Range ◽  
Water Temperature ◽  
River Flow ◽  
Upstream Migration ◽  
Migratory Behaviour ◽  
Pit Tag ◽  
Size Classes ◽  
Total Length ◽  
Vertical Slot ◽  
Inland Rivers

The upstream migratory behaviour of yellow-phase European eels was investigated in regulated inland rivers (>320 km upstream the sea), where the stock is in drastic decline. From 2010 to 2015, eels entering the Belgian Meuse River (n = 1357; total length, 231–755 mm) were caught in fish passes, tagged with a pit-tag and released. Their upstream movements were tracked during the next six consecutive years, using three detection stations installed in vertical-slot fish passes of the Meuse and its Ourthe tributary. Among the 1357 eels tagged, 27.6% (n = 374 individuals) were detected at one or more of the three upstream detection stations. Only 6.6% (n = 89) of tagged eels were detected at the two subsequent stations. In this last group, most of the detected eels continued to move upstream through the Meuse rather than leaving it for the Ourthe. Water temperature >13 °C, river flow 24–226 m3/s, dark time 00:00–05:00 h and the spring–summer seasons were the most important cues for upstream migration. Temperatures and flows at detection did not differ between size classes of ascending eels, while the detection period was earlier and daily speed was faster in large (>450 mm) eels. However, small (≤300 mm) eels moved further upstream at slow speeds because they alternated between short periods of movement and long stationary periods. This behaviour suggests the existence of a few nomad individuals and probably more home range dwellers in the entering population. Small eels were better suited to colonise upper rivers.

ACCES Assessment of Command and Control during a Division-Level CPX, Late Spring 1991 (ACCES Application 91-01)

1992 ◽  
Author(s):  
Jr. Castro ◽  
Collingwood Felix D. ◽  
Ervin Chester E. ◽  
Halpin J. R. ◽  
Stanley M.
Keyword(s):  
Command And Control ◽  
Late Spring ◽  
And Control

Restoring and Controlling the Water Pollution of Endangered River in Bangladesh: A Case Study in Pabna City

2020 ◽  
Vol 3 (2) ◽  
pp. 68-81
Author(s):  
Abu Sadath ◽  
Farhana Afroz ◽  
Hosne Ara ◽  
Abdulla-Al Kafy
Keyword(s):  
Water Pollution ◽  
Local Community ◽  
River Flow ◽  
Low Cost ◽  
Design Approach ◽  
Government Officials ◽  
Conservation Plan ◽  
Policy Measures ◽  
And Control ◽  
Riverfront Development

Rivers are the lifeline of Bangladesh economy and serve as the source of water supply, fisheries, irrigation for agriculture, low-cost transport, generate electricity and conserve biodiversity. The Ichamati River situated in Pabna, Bangladesh is also a blessing for the city. However, recently, due to the irregular and unplanned activities adjacent to the riverside, the life, flow and water quality of the river is in a vulnerable condition. This study aims to identify the present status of the Ichamati River and provide an effective design approach and policy measures in restoring the river flow and control water pollution. The data was collected from the questioner surveys, key informant interviews and focus group discussions. Results suggest that several factors such as the construction of an illegal settlement, unplanned waste dumping, disposal of fiscal sludge through sewerage connection, lack of awareness among people regarding the importance of river biodiversity and absence of riverfront development and conservation plan are responsible for water pollution, inconsistent water flow and damaging the life cycle of Ichamati river. The design approach and policy measures were developed based on the perceptions of local community people, experts and government officials. The suggested policy measures will help to restore the flow of the river and reduce the water pollution, and the design approach will ensure the economic benefit of the riverfront development in future.

scholarly journals Analytical approach for determining the mean water level profile in an estuary with substantial fresh water discharge

2016 ◽  
Vol 20 (3) ◽  
pp. 1177-1195 ◽  
Author(s):  
Huayang Cai ◽  
Hubert H. G. Savenije ◽  
Chenjuan Jiang ◽  
Lili Zhao ◽  
Qingshu Yang
Keyword(s):  
Water Level ◽  
Fresh Water ◽  
River Discharge ◽  
River Flow ◽  
Water Discharge ◽  
Value Theory ◽  
Velocity Amplitude ◽  
Mean Water Level ◽  
The Mean ◽  
Fresh Water Discharge

Abstract. The mean water level in estuaries rises in the landward direction due to a combination of the density gradient, the tidal asymmetry, and the backwater effect. This phenomenon is more prominent under an increase of the fresh water discharge, which strongly intensifies both the tidal asymmetry and the backwater effect. However, the interactions between tide and river flow and their individual contributions to the rise of the mean water level along the estuary are not yet completely understood. In this study, we adopt an analytical approach to describe the tidal wave propagation under the influence of substantial fresh water discharge, where the analytical solutions are obtained by solving a set of four implicit equations for the tidal damping, the velocity amplitude, the wave celerity, and the phase lag. The analytical model is used to quantify the contributions made by tide, river, and tide–river interaction to the water level slope along the estuary, which sheds new light on the generation of backwater due to tide–river interaction. Subsequently, the method is applied to the Yangtze estuary under a wide range of river discharge conditions where the influence of both tidal amplitude and fresh water discharge on the longitudinal variation of the mean tidal water level is explored. Analytical model results show that in the tide-dominated region the mean water level is mainly controlled by the tide–river interaction, while it is primarily determined by the river flow in the river-dominated region, which is in agreement with previous studies. Interestingly, we demonstrate that the effect of the tide alone is most important in the transitional zone, where the ratio of velocity amplitude to river flow velocity approaches unity. This has to do with the fact that the contribution of tidal flow, river flow, and tide–river interaction to the residual water level slope are all proportional to the square of the velocity scale. Finally, we show that, in combination with extreme-value theory (e.g. generalized extreme-value theory), the method may be used to obtain a first-order estimation of the frequency of extreme water levels relevant for water management and flood control. By presenting these analytical relations, we provide direct insight into the interaction between tide and river flow, which will be useful for the study of other estuaries that experience substantial river discharge in a tidal region.

scholarly journals Turbidity in the fluvial Gironde Estuary (southwest France) based on 10-year continuous monitoring: sensitivity to hydrological conditions

2015 ◽  
Vol 19 (6) ◽  
pp. 2805-2819 ◽  
Author(s):  
I. Jalón-Rojas ◽  
S. Schmidt ◽  
A. Sottolichio
Keyword(s):  
River Flow ◽  
Hysteresis Loops ◽  
Annual Runoff ◽  
Transitional Period ◽  
Estuarine System ◽  
Upstream Migration ◽  
Hydrological Conditions ◽  
Frequency Monitoring ◽  
Turbidity Level ◽  
River Floods

Abstract. Climate change and human activities impact the volume and timing of freshwater input to estuaries. These modifications in fluvial discharges are expected to influence estuarine suspended sediment dynamics, and in particular the turbidity maximum zone (TMZ). Located in southwest France, the Gironde fluvial-estuarine system has an ideal context to address this issue. It is characterized by a very pronounced TMZ, a decrease in mean annual runoff in the last decade, and it is quite unique in having a long-term and high-frequency monitoring of turbidity. The effect of tide and river flow on turbidity in the fluvial estuary is detailed, focusing on dynamics related to changes in hydrological conditions (river floods, periods of low discharge, interannual changes). Turbidity shows hysteresis loops at different timescales: during river floods and over the transitional period between the installation and expulsion of the TMZ. These hysteresis patterns, that reveal the origin of sediment, locally resuspended or transported from the watershed, may be a tool to evaluate the presence of remained mud. Statistics on turbidity data bound the range of river flow that promotes the upstream migration of TMZ in the fluvial stations. Whereas the duration of the low discharge period mainly determines the TMZ persistence, the freshwater volume during high discharge periods explains the TMZ concentration at the following dry period. The evolution of these two hydrological indicators of TMZ persistence and turbidity level since 1960 confirms the effect of discharge decrease on the intensification of the TMZ in tidal rivers; both provide a tool to evaluate future scenarios.

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