Abstract:The loss of spawning habitat has been identified as a limiting factor to population 23 growth for lake sturgeon, Acipenser fulvescens, the most widely distributed species of the family 24 in North America. While local information exists about lake sturgeon spawning habitat, a 25 synthesis of all available data is needed across its range. Our study used meta-analytical 26 techniques to describe the mean and range of critical spawning habitat characteristics based on 27 data from 48 sites across all major watersheds in which lake sturgeon are found. Data were 28 compiled into univariate habitat suitability indices to describe the spawning niche. Results

Despite a widespread acknowledgment that river restoration projects sometimes fail due to a poor understanding of geomorphology and hydrology, there are relatively few published case studies reporting failures, particularly for nonsalmonid species such as Lake Sturgeon Acipencer fulvescens. We used a three‐dimensional hydrodynamic model to retroactively assess a restoration project in the 80‐m‐wide Ouareau River, Quebec which did not meet its objective of providing additional spawning habitat for Lake Sturgeon. Virtual modifications of the bathymetry allowed for the flow field to be simulated with and without instream structures (boulder weirs) constructed in 2007 for four discharges representing flow conditions during spawning. Simulated velocities and flow depths were used to determine the suitability of the site and to assess the impact of the instream structures. Results revealed that instream structures did not meet the expectation of raising water levels and had no significant impact on river velocity. Furthermore, there was sufficient good quality habitat within the study area before restoration, and artificial spawning sites were placed in locations with nonoptimal velocities for spawning Lake Sturgeon. A comparison with a successful Lake Sturgeon restoration project in the St. Clair–Detroit River system revealed marked differences in restoration strategies, which likely explain the different outcomes of these two projects. These results point to the need for (1) adaptive management protocols that include an iterative decision‐making process to allow for adjustments in hypotheses and strategies to improve the management process, (2) multidisciplinary input, including hydrogeomorphology, and (3) a more systematic use of two‐dimensional or three‐dimensional numerical models prior to the implementation of instream structures in river restoration projects.

Vortex rock weirs (VRW) are often used in natural channel design applications to maintain channel form and function, provide physical channel stability, and enhance aquatic habitats. A balanced approach is required to address (often) conflicting goals of VRWs, which include providing erosion protection and grade control while facilitating fish passage for target species. This research evaluated a sequence of modified VRWs in a small-scale watercourse in Southern Ontario, Canada. To determine passage suitability for the target fish species, the water level, water temperature, and channel geometries at 10 VRWs and 11 adjacent pools were monitored under different water level conditions. The structural dimensions and velocity at each VRW were compared to the burst swim speed of local small-bodied fish species to determine fish passage suitability and identify the best practices for VRW design and construction. The results concluded that VRWs provided suitable passage for small-bodied fish species through gap and over-weir flow pathways, particularly during low water level conditions. Further, appropriate design considerations based on the VRW gradient, VRW width, keystone size, and pool length contributed to 100% fish ‘passability’ under all water level conditions. The methodology is provided for predicting the velocity and small-bodied fish passage suitability through VRWs, informing the best practices for VRW design and construction while balancing the requirements for channel stability and fish passage, and contributing to fish population management strategies.

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