The influence of system settings on positioning accuracy in acoustic telemetry, using the YAPS algorithm

Background: Acoustic positioning telemetry allows to collect large amounts of data on the movement of aquatic animals by use of autonomous receiver stations. Essential in this process is the conversion from raw signal detections to reliable positions. A new advancement in the domain is Yet Another Positioning Solver (YAPS), which combines the detection data on the receivers with a model of animal movement. This transparent, flexible and on-line available positioning algorithm overcomes problems related to traditional point-by-point positioning and filtering techniques. However, its performance has only been tested on data from one telemetry system, providing transmitters with stable burst interval. To investigate the performance of YAPS on different system parameters and settings, we conducted a simulation study. Results: This paper discusses the effect of varying burst types, burst intervals, number of observations, reflectivity levels of the environment, levels of out-of-array positioning and temporal receiver resolution on positioning accuracy. We found that a receiver resolution better than 1 ms is required for accurate fine-scale positioning. The positioning accuracy of YAPS increases with decreasing burst intervals, especially when the number of observations is low, when reflectivity is high or when information out-of-array is used. However, when the burst interval is stable, large burst intervals (in the order of 1 to 2 min) can be chosen without strongly hampering the accuracy (although this results in information loss). With random burst intervals, the accuracy can be much improved if the random sequence is known. Conclusions: As it turns out, the key to accurate positioning is the burst type. If a stable burst interval is not possible, the availability of the random sequence improves the positioning of random burst interval data significantly

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

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

Over the last 40 years, Anguilla species in the northern hemisphere have shown a strong decline in recruitment. Due to a 98% recruitment decline, the European eel is now classified as critically endangered according to the IUCN Red List. To aid conservation and recovery of European eel populations, the European Union recently adopted a Council Regulation which imposes a management system that ensures 40% escapement of the spawning stock biomass, defined as the best estimate of the theoretical escapement rate if the stock were completely free of anthropogenic influences. Various causes likely contribute to the eel decline (e.g. pollution, human-introduced parasites, changes in ocean climate, habitat deterioration…), but habitat fragmentation by migration barriers that prevent the movement of silver eels between freshwater and the sea is probably one of the most important bottlenecks. During the last decades, a substantial number of canals has been developed, creating new habitat for eels. However, eel migration and potential obstacles in these systems are still underexplored. In this study, we tracked 131 European eels (Anguilla anguilla L.) from October 2014 till March 2017 in the Belgian Albert Canal with acoustic telemetry. The 130-km long canal is on average 86 m wide, 5 m deep and functions as a shipping route between the rivers Schelde and Meuse. The canal has a highly regulated water flow and six shipping locks to overcome the 56-m fall, which may have a negative impact on silver eel escapement. Indeed, we found significant delays (i.e. periods with a significantly prolonged residence time) and a ca 50% lower swimming speed near shipping locks compared to riverine conditions. Depending on nothing but their accumulated fat for migration to their spawning grounds, delays can seriously impact eels by wasting precious energy resources needed for a successful trans-Atlantic migration

Emigration of European silver eel (Anguilla anguilla L.) from a polder system into the Schelde estuary

Connectivity between freshwater habitats and marine areas is heavily obstructed by migration barriers, leading to a high pressure on diadromous eel populations. Migration barriers attribute to the 98% decline of the European eel (Anguilla anguilla L.) population. A better understanding of eel behaviour regarding these barriers is needed for water managers to take proper mitigation actions. We tracked 50 eels by means of acoustic telemetry between July 2012 and January 2015 and analysed their migration behaviour in a Belgian polder area. On their way to the Schelde Estuary, eels face several migration barriers such as a pumping station, a weir and tidal barriers. The telemetry study did reveal significant delays and searching behaviour near those barriers. Depending on nothing but their accumulated fat, delays can have a serious impact on the fitness of the eel by wasting precious energy resources needed for a successful trans-Atlantic migration. In addition, delays and searching behaviour can also increase predation risk. The obtained knowledge can contribute to efficient management such as improved fish passage and guidance solutions

Trying to choose the less bad route: Individual migratory behaviour of Atlantic salmon smolts (Salmo salar L.) approaching a bifurcation between a hydropower station and a navigation canal

Contrary to small- and medium-sized rivers, little attention has been paid to the downstream migration of Atlantic salmon smolts in large-sized rivers and the size-related impact of hydropower stations. From 2014 to 2016, we investigated the downstream migration of n=72 acoustic-tagged smolts in the Meuse river at a bifurcation zone between a hydropower station equipped with three Kaplan turbines and a navigation canal. A hydrodynamic model that solves the depth-integrated shallow water equations on a Cartesian grid using a finite volume technique was used to infer the influence of water discharge and flow velocity on the smolts’ behaviour upstream of the hydroelectric complex. Of the migrating smolts, 41.5 % performed back and forth movements before approaching the complex for the first time, sometimes over long distances and at a slow pace, leading to significant delays (3‒298 h). Beyond about 250 m3 s-1, the water flow direction changes towards the hydropower station with a gradual acceleration. A median water discharge of 161 m3 s-1 and associated median flow velocity of 0.14 m s-1 tended to favour a more direct and downstream movement towards the hydropower station. On the other hand, the navigation canal was mainly approached at low water discharge (median 132 m3 s-1), due to a higher flow velocity (median 0.11 m s-1) at the entrance. Of the released smolts, only 38.6 % passed through the complex, of which 36.4 % migrated by the navigation canal and 63.6 % by the hydropower station, with a median research time of 04:44. Among all the released individuals, the escapement rate at the end of the study site was 2.9 % by the canal and 8.3 % by the Meuse river. This site, which offers two non-optimal, unattractive and unsafe migration routes, turns out to be problematic for successful downstream smolt migration

How to select patients for anti-reflux surgery? The ICARUS guidelines (International Consensus regarding preoperative examinations and clinical characteristics assessment to select adult patients for AntiReflUx Surgery)

Objective: Anti-reflux surgery can be proposed in patients with gastro-esophageal reflux disease, especially when proton pump inhibitor use leads to incomplete symptom improvement. However, to date, international consensus guidelines on the clinical criteria and additional technical examinations used in patient selection for anti-reflux surgery are lacking. We aimed at generating key recommendations in the selection of patients for anti-reflux surgery. Design: We included 35 international experts (gastroenterologists, surgeons and physiologists) in a Delphi process and developed 37 statements that were revised by the Consensus Group, to start the Delphi process. Three voting rounds followed where each statement was presented with the evidence summary. The panel indicated the degree of agreement for the statement. When 80% of the Consensus Group agreed (A+/A) with a statement, this was defined as consensus. All votes were mutually anonymous.Results: Patients with heartburn with a satisfactory response to PPIs, patients with a hiatal hernia (HH), patients with esophagitis LA grade B or higher and patients with Barrett’s esophagus are good candidates for anti-reflux surgery. An endoscopy prior to anti-reflux surgery is mandatory and a barium swallow should be performed in patients with suspicion of a HH or short esophagus. Esophageal manometry is mandatory to rule out major motility disorders. Finally, esophageal pH (+/- impedance) monitoring off PPI is mandatory to select patients for anti-reflux surgery, if endoscopy is negative for unequivocal reflux esophagitis. Conclusion: With the ICARUS guidelines, we generated key recommendations for selection of patients for anti-reflux surgery