Behavioural salinity preferences of juvenile green sturgeon Acipenser medirostris acclimated to fresh water and full‐strength salt water

To quantify the salinity preference of juvenile green sturgeon Acipenser medirostris, two groups of A. medirostris [140 days post hatch (dph); total length (L_T) 38·0–52·5 cm] were acclimated to either near fresh water (mean ± s.e . salinity = 3·2 ± 0·6) or full‐strength salt water (34·1 ± 1·2) over 8 weeks. Following acclimation, the two groups were divided into experimental and control groups, where experimental A. medirostris from both freshwater and saltwater acclimations were individually introduced (200–220 dph) into a rectangular salinity‐preference flume (maximum salinity gradient: 5–33). Control A. medirostris were presented with only their acclimation water (fresh water or salt water) on both sides of the flume. It was demonstrated that A. medirostris acclimated to both salt water and fresh water spent a significantly greater amount of time on the side of the testing area with the highest salinity concentration (P < 0·05 and P < 0·001, respectively) while control A. medirostris spent an equal amount of time on each side of the flume. These findings indicate that juvenile A. medirostris are not only capable of detecting salt water within the first year of their lives but perhaps are actively seeking out saline environments as they move through a watershed. Establishing A. medirostris salinity preferences provides a better understanding of the early life history of this threatened species, shedding light on possible outmigration timing.     

When is stream invertebrate drift catastrophic? The role of hydraulics and sediment transport in initiating drift during flood events

1. The term ‘catastrophic drift’ is used to describe the large‐scale displacement of invertebrates that occurs during periods of increased river discharge. However, the physical processes that lead to animals entering the water column at such times remain poorly understood. Specifically, the hypothesis that the movement of bed sediments during floods triggers a large increase in drift has lacked a rigorous field test. 2. Using a portable flume, the hydraulic conditions and rates of bedload transport associated with small, frequent floods were created in situ within a reach of a gravel bed river. Experiments focussed on the patches of fine sediment which are the dominant source of bed material transported during small floods. The flume produced near bed velocities of up to 2 m s^?1 over the patches, increasing shear stress, initiating sediment transport and causing invertebrates to enter the drift. 3. The total number of individuals lost from the bed, as well as the taxonomic composition of the drift, were influenced strongly by shear stress and bedload. The rate of loss from the bed was low at shear stresses <9 dynes cm^?2 (0–4 individuals min^?1 from the 0.5 m² flume bed area). Once shear stress exceeded 9 dynes cm^?2, the threshold that resulted in consistent bedload transport from the patches, the rate of loss of animals increased to a maximum of 56 individuals min^?1. When bedload transport rates were at their highest, the taxonomic composition of the drift was more similar to the benthos than it was to the drift observed when bed material was stable. 4. Absolute rates of bedload transport created by the manipulations were extremely low (<7 g m^?1 s^?1) and typical of those measured during small, frequent floods. Events of this magnitude do not break up the armour layer across the reach as a whole and so exposed patches of fine sediment are the principal source of bedload material. Consequently, discharge events not considered as disturbances in geomorphic terms may initiate frequent episodes of so‐called ‘catastrophic drift’ from patches of stream bed.     

运用水槽对优秀青少年游泳运动员有氧能力的研究

目的:通过运用水槽对上海优秀青少年游泳运动员有氧能力进行测试,掌握其有氧能力水平。方法:运用游泳水槽进行递增负荷测试,测试最大摄氧量(VO2max)、相对最大摄氧量(VO2max/kg)、呼吸熵(RQ)、最高乳酸(BLamax)和乳酸恢复率(RQ%)等指标。结果:男、女运动员的起始速度为1.20 m/s和1.16 m/s,每分钟递增0.04 m/s的VO2max测试模式是青少年运动员的适宜模式;上海优秀青少年男子和女子游泳运动员VO2max/kg分别为(59.06±5.20)ml/(min.kg)和(57.20±2.81)ml/(min.kg)。结论:上海优秀男、女青少年游泳运动员的VO2max/kg低于国外优秀运动员,乳酸清除代谢的能力强于国内运动员。     

Evaluation of swimming performance for fish passage of longnose dace Rhinichthys cataractae using an experimental flume

The swimming performance of longnose dace Rhinichthys cataractae, the most widely distributed minnow (Cyprinidae) in North America, was assessed in relation to potential passage barriers. The study estimated passage success, maximum ascent distances and maximum sprint speed in an open‐channel flume over a range of water velocities and temperatures (10·7, 15·3 and 19·3° C). Rhinichthys cataractae had high passage success (95%) in a 9·2 m flume section at mean test velocities of 39 and 64 cm s^–1, but success rate dropped to 66% at 78 cm s^–1. Only 20% of fish were able to ascend a 2·7 m section with a mean velocity of 122 cm s^–1. Rhinichthys cataractae actively selected low‐velocity pathways located along the bottom and corners of the flume at all test velocities and adopted position‐holding behaviour at higher water velocities. Mean volitional sprint speed was 174 cm s^–1 when fish volitionally sprinted in areas of high water velocities. Swimming performance generally increased with water temperature and fish length. Based on these results, fishways with mean velocities <64 cm s^–1 should allow passage of most R. cataractae. Water velocities >100 cm s^–1 within structures should be limited to short distance (<1 m) and structures with velocities ≥158 cm s^–1 would probably represent movement barriers. Study results highlighted the advantages of evaluating a multitude of swimming performance metrics in an open‐channel flume, which can simulate the hydraulic features of fishways and allow for behavioural observations that can facilitate the design of effective passage structures.     

Ecological management of aquatic plants: effects in lowland streams

Recently, a significant increase in macrophyte growth has been observed in many lowland rivers in Flanders, mainly due to eutrophication and an improvement of the water quality. This growth strongly influences the channel roughness (Manning-n). The first purpose of the project was a better understanding of the complex relationship between biomass development and discharge capacity in lowland rivers. In order to avoid the backing up of water upstream, the whole vegetation body is usually mowed annually. This project also investigated a lighter ecological management of aquatic plants in which only a part of the vegetation is removed in separate and alternating blocks, seeking a compromise between sufficient discharge and conserving large parts of the macrophyte vegetation with all its functions. Beside laboratory experiments, field survey was undertaken in the Grote Caliebeek, a tributary of the Kleine Nete in Flanders, Belgium. The results indicated that the presence of macrophytes in lowland rivers slowed down the waterflow and resulted in a raised water level. The upstream water level followed biomass development at a certain discharge level. The mowing experiments and the field survey indicated that alternating weed cutting patterns can reduce fall in an effective way. This research emphasizes the possibilities of alternating weed cutting patterns in order to deal with water flow problems. In the long term there will be the need for a better understanding of the ecological relationships in the search for a sustainable integrated method of controlling aquatic vegetation.     

First evidence of attraction of adult river lamprey in the migratory phase to larval odour

Sexually immature, adult river lamprey Lampetra fluviatilis in the upstream migratory phase, were shown to be attracted to water conditioned with ammocoete larvae when tested using a two‐choice flume. Although preliminary, the data suggest that migrating adult river lamprey may be attracted to larval putative pheromone as recorded in sea lamprey Petromyzon marinus .     

Experimental quantification of the swimming performance and behaviour of spawning run river lamprey Lampetra fluviatilis and European eel Anguilla anguilla

Using a large-scale open-channel flume, the swimming ability and behaviour of individual adult European eel Anguilla anguilla and river lamprey Lampetra fluviatilis, species that exhibit anguilliform locomotion, were quantified under complex hydraulic conditions created by a 0·2-0·3 m high under- or overshot weir during four discharge regimes. Fishes were allowed to approach the weirs from both up- and downstream. All fishes passed the undershot weir, independent of discharge and direction of movement, and under high flow (mean ±S.E. 194·63 ± 6·48 l s(-1)) moved upstream against velocities that ranged between 1·75 and 2·12 m s(-1), suggesting greater maximum swimming capability than previously reported. In comparison, passage efficiency during upstream movement was lower for the overshot weir for both L. fluviatilis and A. anguilla. Downstream moving A. anguilla took longer to pass the over- than undershot weir. This study describes a methodology to attain realistic measures of swimming ability and behavioural performance required to develop multispecies fish passage criteria.     

Measuring Ucrit and endurance: equipment choice influences estimates of fish swimming performance

This study compared the critical swimming speed (U_crit) and endurance performance of three Australian freshwater fish species in different swim‐test apparatus. Estimates of U_crit measured in a large recirculating flume were greater for all species compared with estimates from a smaller model of the same recirculating flume. Large differences were also observed for estimates of endurance swimming performance between these recirculating flumes and a free‐surface swim tunnel. Differences in estimates of performance may be attributable to variation in flow conditions within different types of swim chambers. Variation in estimates of swimming performance between different types of flumes complicates the application of laboratory‐based measures to the design of fish passage infrastructure.