The effects of hydrodynamics on the three-dimensional downstream migratory movement of Atlantic salmon.

Anthropogenic structures in rivers are major threats for fish migration and effective mitigation is imperative given the worldwide expansion of such structures. Fish behaviour is strongly influenced by hydrodynamics, but little is known on the relation between hydraulics and fish fine scale-movement. We combined 3D Computational fluid dynamics modelling (CFD) with 2D and 3D fish positioning to investigate the relation between hydrodynamics and the downstream movement of Atlantic salmon smolts (Salmo salar). We show that fish use fine-scale flow velocity and turbulence as navigation cues of fine-scale movement behaviour. Tri-dimensional swimming speed and swimming direction can be explained by adjustments of fish to flow motion, which are linked to fish swimming mode. Fish diverge from the flow by swimming at speeds within or higher than their prolonged speeds (0.38-0.73 m s-1). Flow direction plays a pivotal role on fish swimming performance, with high upstream and downwards velocities impacting swimming the most. Turbulence is also influential, by benefiting swimming performance at low TKE (< 0.03 m2 s-2) or constraining it at higher levels. We show that fish behaviour is affected by interactions of several hydraulic variables that should be considered jointly.

Hydropower and fish - Report and messages from workshop on research and innovation in the context of the European policy framework.

Hydropower is the world's largest renewable electricity source and will have an important role in the future energy system with increased requirements to integrate environmental and socioeconomic aspects of sustainability. One important field of interaction is between hydropower and fish. The aim of optimizing hydropower production as well as fish production via Research and Innovation in the context of the European policy framework was the topic of the workshop "Hydropower and Fish - Research and Innovation in the context of the European Policy Framework" organized in May 2017 in Brussels. This paper reports the main messages from the workshop sessions including future research needs, collaboration strategies and knowledge exchange. In particular, the workshop emphasized the need for standardized monitoring and mitigation approaches and of following a balanced approach in addressing challenges between renewable energy production and river and fish ecology. Future research in the area is needed. As perspective and primer for future discussions, the interrelations of hydropower and fish to the different spheres of the total environment are presented and discussed.

Severe mortality in wild Atlantic salmon Salmo salar due to proliferative kidney disease (PKD) caused by Tetracapsuloides bryosalmonae (myxozoa).

Extensive mortality in Atlantic salmon fry was reported in the River Aelva from 2002 to 2004. Dead fish were collected in late summer 2006, and live fish were sampled by electrofishing in September the same year. At autopsy and in histological sections, the fish kidneys were found to be pale and considerably enlarged. Proliferative lesions with characteristic PKX cells were seen in a majority of the fish. DNA from kidney samples of diseased fish was subjected to PCR and sequencing, and the amplified sequences matched those of Tetracapsuloides bryosalmonae. We concluded that this myxozoan transmitted from bryozoans was the main cause of the observed mortality in salmon fry in 2006. Results from quantitative electrofishing in 2005 and 2006, combined with the observed fry mortality from 2002 to 2004, show that the smolt production in the river is severely reduced and that T. bryosalmonae is the most likely explanation for this decline. The present study is the first to report a considerable negative population effect in wild Atlantic salmon due to proliferative kidney disease (PKD). It also represents the northernmost PKD outbreak in wild fish. The river is regulated for hydroelectric power purposes, causing reduced water flow and elevated summer temperatures, and the present PKD outbreak may serve as an example of increased disease vulnerability of northern fish populations in a warmer climate.