Summary1. The presence of dams, stream-road crossings, and other infrastructure often compromises the connectivity of rivers, leading to reduced sh abundance and diversity. The assessment and mitigation of river barriers is critical to the success of restoration eorts aimed at restoring river integrity.2. In this paper, we present a combined modeling approach involving statistical regression methods and mixed integer linear programming to maximize resident sh species richness within a catchment through targeted barrier mitigation. Compared to existing approaches, our proposed method provides enhanced biological realism while avoiding the use of complex and computationally intensive population/ecosystem models.3. To estimate barrier passability quickly and at low cost, we further outline a rapid barrier assessment methodology. The methodology is used to characterize potential passage barriers for various sh species common to the UK but can be readily adapted to dierent planning areas and other species of interest. 4. We demonstrate the applicability of our barrier assessment and prioritization approach based on a case study of the River Wey, located in south-east England. We nd that signicant increases in species richness can be achieved for modest investment in barrier mitigation. In particular, dams and weirs with low passability located on mid to high order streams are identied as top priorities for mitigation.5. Synthesis and applications. Our study shows the benets of combining a coarse resolution barrier assessment methodology with state-of-the art optimization modeling to cost-eectively plan sh passage barrier mitigation actions. The modeling approach can help inform on-the-ground river restoration decision making by providing a recommended course of action that best allocates limited resources in order to restore longitudinal connectivity and maximize ecological gains.

The effect of Anguillicola crassus, Pseudodactylogyrus bini and Pseudodactylogyrus anguillae infection on the behaviour of downstream migrating adult European eels Anguilla anguilla as they encountered accelerating water velocity, common at engineered structures where flow is constricted (e.g. weirs and bypass systems), was evaluated in an experimental flume. The probability of reacting to, and rejecting, the velocity gradient was positively related to A. crassus larval, adult and total abundance. High abundance of Pseudodactylogyrus spp. reduced this effect, but A. crassus was the strongest parasitic factor associated with fish behaviour, and abundance was positively related to delay in downstream passage. Delayed downstream migration at hydraulic gradients associated with riverine anthropogenic structures could result in additional energetic expenditure for migrating A. anguilla already challenged by A. crassus infection.

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Ecological Engineering xxx (2015) pp. xxx-xxxInfluence of corrugated boundary hydrodynamics on the swimming performance and behaviour of juvenile common carp (Cyprinus carpio) L.R. Newbold, P.S. Kemp * Carp swimming performance and behavioural response to corrugations were assessed.Corrugations did not improve swimming performance compared to smooth walls. Fish could occupy low velocity areas within large and medium corrugation troughs.Fish often swam in higher velocity, lower TKE flow, away from larger corrugations.Turbulence near the corrugated walls may have reduced fish stability.Ecological Engineering xxx (2015) xxx-xxx Although occupation of the MC and LC troughs occurred, many individuals spent little time here, and areas with lower TKE were often occupied. Under the experimental conditions created, this study does not support the assumption that low velocity areas created by wall corrugations will improve culvert passage.

Installation of baffles intended to improve fish passage through culverts can reduce discharge capacity and trap debris, increasing flood risk. A sloping upstream face may reduce this risk,but new designs must be tested for fish passage efficiency. The European eel (Anguilla anguilla) is a critically endangered species, yet the suitability of even common baffle types to aid upstream movement has not been tested. This study compared the water depth, velocity, turbulent kinetic energy (TKE), and upstream passage performance of adult yellow-phase eels, between three 6 m long culvert models: smooth and unmodified (control); containing corner baffles (treatment 1); and with prototype sloped baffles installed (treatment 2).Passage of individual fish was assessed during 25 one-hour trials per model. Performance was quantified as entrance efficiency, number of entries per fish, passage efficiency, and overall efficiency. Total and passage delay, and successful passage time were also evaluated.Despite some individuals being able to swim against unexpectedly high water velocities (> 1.5 m s -1 for 4 m), passage performance in the control was poor, with an overall efficiency of 28%. Compared to the control, both treatments increased the mean centreline water depth by approximately 0.11 m, created heterogeneous flow conditions with low velocity resting areas, and reduced maximum velocities. As a result, entrance rate and all efficiency parameters were higher for the treatments than for the control (overall efficiency = 84%), despite longer passage delay. The TKE was slightly higher in treatment 2 than 1, but there was no difference in water depth or overall efficiency. The findings show that both corner and sloped baffles can mitigate for impeded upstream adult eel movement. The extent to which the sloping upstream face will improve debris transport should be explored further.