Fish Behaviour in the Vicinity of a Navigation Lock Complex: the Challenges

Hydraulic structures such as navigation locks, pumping stations and hydropower plants play an important role in navigation, water management and sustainable energy production. However, these structures may severely impact the aquatic ecosystem and freshwater fish in particular. In Belgium, the Albert Canal connecting the river Meuse to the river Scheldt, is an important migration route for European eel (Anguilla anguilla, critically endangered) and Atlantic salmon (Salmo salar, vulnerable). Both species have a downstream migrating phase in their lifecycle (respectively silver eels and salmon smolts), during which they are hampered by hydraulic structures. In the coming years, Archimedes screws are to be installed at the navigation lock complexes present in the Flemish part of the canal, which can function both as pumping stations and hydropower generators. A first installation is already present at the navigation lock complex of Kwaadmechelen. Before fish mitigation measures can be implemented, it is important to gain understanding on how the downstream migrating fish are affected by hydrodynamics around the complex. In this paper, we focus on the challenges in investigating fish behaviour, related to the acoustic telemetry used to determine fish positions, as well as on the complexity of a hydrodynamic CFD model for the studied site. Additionally, we present some preliminary results. In the next phase of the research, observed fine-scale behaviour of the fish in front of the navigation lock complex will be compared with predicted flow patterns by means of a CFD model

Spatio-temporal analysis of fish behaviour: lessons learnt to stimulate fish passage

Obstacles like weirs, watermills and locks are barriers for migratory fish. The fact that specific fish species cannot reach their optimal spawning habitat can have severe consequences for the survival of these species. While numerous fish passage types have been designed to solve this problem, these are sometimes not efficient. More insight into fish behavior is needed to improve fish pass efficiency, and acoustic telemetry allows such detailed observation of spatio-temporal migration patterns. We present novel findings on fish behavior at anthropogenic structures based on acoustic telemetry. The impact of several constructions like sluices, weirs, pumping stations and small-scale hydropower plants will be assessed and potential solutions to enhance fish migration at these structures will be discussed. This approach will identify crucial information needs for effective fish passage management and reveal a range of opportunities for fish passage research

European silver eel (<i>Anguilla anguilla</i> L.) migration behaviour in a highly regulated shipping canal

Among the many man-made structures that facilitate shipping, navigable canals take an important position. These canals may offer energetically favourable migration routes for diadromous fish, but they may also obstruct fish migration, for instance at shipping locks. Because the use of shipping canals by, and their effects on, migrating fish remain unknown, we assessed whether these canals can play a significant role in the migration of the critically endangered European eel. Only one third of 70 acoustically tagged silver eels completed migration through a shipping canal, and did so at a very low pace (average -1) due to delays at shipping locks and most likely also due to the disruption of water flow. These delays may come at an energetic cost, hampering the chances of successful migration. Knowledge on the impact of shipping canals on diadromous fish is crucial for proper management regulations. For instance, the observation that eels mostly migrated at night and during spring and autumn can support water managers to define adequate measures to improve eel migration in shipping canals

Kan Vlaanderen het tij nog keren voor de Europese paling? Effecten van tien jaar Europese bescherming op het voortbestaan van de Paling in Vlaanderen

Despite the many restoration measures launched to prevent the Eelfrom further decline, glass eel recruitment and yellow eel density remain troublesome. Eel life is challenging in Flemish waters, where migration routes are blocked by barriers, where unnatural banks and toxic substances hamper growth and reproductive capacity and where pumping stations abruptly end many Eels’ lives. In spite of high levels of pollutants in its meat, Eels still end up on anglers plates (ca. 30 tons/year). Urgent actions are needed to increase the amount of easily accessible high-quality watercourses with more natural flow dynamics. As long as the tides are not turned, a more vigorous European policy on the restriction of the Eel fishery (including elvers) seems indispensable

Capacitive water release and internal leaf water relocation delay drought-induced cavitation in African Maesopsis eminii

© 2016 The Author. The impact of drought on the hydraulic functioning of important African tree species, like Maesopsis eminii Engl., is poorly understood. To map the hydraulic response to drought-induced cavitation, sole reliance on the water potential at which 50% loss of xylem hydraulic conductivity (?50) occurs might be limiting and at times misleading as the value alone does not give a comprehensive overview of strategies evoked by M. eminii to cope with drought. This article therefore uses a methodological framework to study the different aspects of drought-induced cavitation and water relations in M. eminii. Hydraulic functioning of wholebranch segments was investigated during bench-top dehydration. Cumulative acoustic emissions and continuous weight measurements were used to quantify M. eminii's vulnerability to drought-induced cavitation and hydraulic capacitance. Wood structural traits, including wood density, vessel area, diameter and wall thickness, vessel grouping index, solitary vessel index and vessel wall reinforcement, were used to underpin observed physiological responses. On average, M. eminii's 50 (±SE) was -1.9 ± 0.1 MPa, portraying its xylem as drought vulnerable, just as one would expect for a common tropical pioneer. However, M. eminii additionally employed an interesting desiccation delay strategy, fuelled by internal relocation of leaf water, hydraulic capacitance and the presence of parenchyma around the xylem vessels. Our findings suggest that exclusive dependence on 50 would have misdirected our assessments of M. eminii's drought stress vulnerability. Hydraulic capacitance linked to anatomy and leaf-water relocation behaviour was equally important to better understand M. eminii's drought survival strategies. Because our study was conducted on branches of 3-year-old greenhouse-grown M. eminii seedlings, the findings cannot be simply extrapolated to adult M. eminii trees or their mature wood, because structural and physiological plant properties change with age. The techniques and methodological framework used in this study are, however, transferable to other species regardless of age