Finding navigation cues near fishways.

Many fish species depend on migration for various parts of their life cycle. Well-known examples include diadromous fish such as salmon and eels that need both fresh water and salt water to complete their life cycle. Migration also occurs within species that depend only on fresh water. In recent decades, anthropogenic pressures on freshwater systems have increased greatly, and have resulted, among other effects, in drastic habitat fragmentation. Fishways have been developed to mitigate the resulting habitat fragmentation, but these are not always effective. To improve fishway efficiency, the variety of navigation cues used by fish must be better understood: fish use a multitude of sensory inputs ranging from flow variables to olfactory cues. The reaction of a fish is highly dependent on the intensity of the cue, the fish species involved, and individual traits. Recently developed monitoring technologies allow us to gain insights into different combinations of environmental and physiological conditions. By combining fish behavioural models with environmental models, interactions among these components can be investigated. Several methods can be used to analyse fish migration, with state-space models, hidden Markov models, and individual-based models potentially being the most relevant since they can use individual data and can tie them to explicit spatial locations within the considered system. The aim of this review is to analyse the navigational cues used by fish and the models that can be applied to gather knowledge on these processes. Such knowledge could greatly improve the design and operation of fishways for a wider range of fish species and conditions.

Individual based models for the simulation of fish movement near barriers: Current work and future directions.

River fragmentation is an increasing issue for water managers and conservationists. Barriers such as dams interfere with freshwater fish migration, leading to drastic population declines. While there are a range of widely implemented mitigation approaches, e.g. fish passes, such measures are often inefficient due to suboptimal operation and design. There is increasing need to be able to assess mitigation options prior to implementation. Individual based models (IBMs) are a promising option. IBMs can simulate the fine-scale movement of individual fish within a population as they attempt to find a fish pass, incorporating movement processes themselves. Moreover, IBMs have high transferability to other sites or conditions (e.g. changing mitigation, change in flow conditions), making them potentially valuable for freshwater fish conservation yet their application to the fine-scale movement of fish past barriers is still novel. Here, we present an overview of existing IBMs for fine-scale freshwater fish movement, with emphasis on study species and the parameters driving movement in the models. In this review, we focus on IBMs suitable for the simulation of fish tracks as they approach or pass a single barrier. The selected IBMs for modelling fine-scale freshwater fish movement largely focus on salmonids and cyprinid species. IBMs have many applications in the context of fish passage, such as testing different mitigation options or understanding processes behind movement. Existing IBMs include movement processes such as attraction and rejection behaviours, as reported in literature. Yet some factors affecting fish movement e.g. biotic interactions are not covered by existing IBMs. As the technology available for fine scale data collection continues to advance, such as increasing data linking fish behaviour to hydraulics, IBMs could become a more common tool in the design and implementation of fish bypass structures.

Depth-dependent hydraulic roughness and its impact on the assessment of hydropeaking.

Hydrodynamic river models in combination with physical habitat modelling serve as the basis for a wide spectrum of environmental studies. Larvae, juvenile and spawning fish, redds and benthic invertebrates belong to the biological groups most heavily affected by rapid flow variations as a consequence of peaking energy production, or "hydropeaking". As these species find their preferential habitat to a great extent in shallow regions, high prediction accuracy for these areas is essential to substantiate the use of hydrodynamic models. In this paper, a new formulation for the depth-dependent roughness originating from the boundary layer theory is derived. The modelling approach is based on the concept of a dynamic, spatio-temporal Manning's roughness which allows for considerable improvement in the accuracy of stationary and highly transient hydrodynamic simulations in shallow river areas. In addition, the approach facilitates more effective model calibration, as it allows for the preservation of the roughness sublayer thickness as a single calibration parameter for the entire range of hydropeaking discharges. The approach is tested and validated on a 7.5km long stretch of a middle-size gravel river affected by hydropeaking. Model results using conventional constant roughness and the proposed dynamic roughness approaches are compared. The implications for the stationary habitat assessment and calculation of dynamic hydropeaking parameters are analysed as well.