We examined the effectiveness of three fishpasses (two gabion‐style pool–weir fishpasses and one nature‐like choke‐and‐pool fishpass) at enhancing connectivity among three small, headwater lakes as part of a fish habitat compensation project in the Barrenlands region of the Northwest Territories. We quantified fish attraction and passage efficiency of fishpasses using PIT antennae, and compared fish use of fishpasses to reference streams using visual and electrofishing surveys for 1 year before and 2 years after their construction. We did not detect, observe, or capture any fish in either of the gabion‐style pool–weir fishpasses during the first year after construction, and these two fishpasses were subsequently retrofitted to improve their hydraulic performance. After retrofits were completed, we still did not detect any tagged fish (≥150 mm) migrating through the two fishpasses using PIT telemetry, but identified some small fish moving downstream through these fishpasses during visual and electrofishing surveys. Conversely, we detected tagged Arctic Grayling Thymallus arcticus migrating upstream and downstream through the nature‐like choke‐and‐pool fishpass during both postenhancement years, and also encountered fish throughout this fishpass during visual and electrofishing surveys. Compared with reference streams, gabion‐weir fishpasses limited fish movement and use even after modification, whereas the nature‐like fishpass successfully facilitated fish movement and use. We recommend against using gabion‐style pool–weir fishpasses in Barrenlands headwater lake–stream systems, particularly when stream flow is limited, and suggest future projects aimed at enhancing lake–stream connectivity explore nature‐like fishpass designs in an experimental management framework.

Sperm-dependent asexual species must coexist with a sexual species (i.e. a sperm source) to reproduce. The maintenance of this coexistence, and hence the persistence of sperm-dependent asexual species, may depend on ecological niche separation or preference by males for conspecific (i.e. sexual) mates. We first modified an analytical model to consider both of these mechanisms acting simultaneously on the coexistence of the two species. Our model indicates that a small amount of niche separation between parental species and hybrids can facilitate coexistence by weakening the requirement for male mate preference. We also estimated niche separation empirically in the Chrosomus (formerly Phoxinus) sexual-asexual system based on diet overlap between sperm-dependent asexuals and their two sexual host species. Diet overlap between the sexual species was not significant in either lake, whereas the sperm-dependent asexual had an intermediate niche that overlapped significantly, but somewhat asymmetrically, with both sexual species. These empirical results were then used to parameterize our analytical model to predict the minimum strength of male mate preference required to maintain coexistence in each lake. Some male mate preference is likely required to maintain coexistence in the Chrosomus system, but the minimum required preference depends on the severity of density dependence. Future empirical work on understanding coexistence in sperm-dependent asexual systems would benefit from taking both niche separation and mate choice into account, and from simultaneous empirical estimates of male mate choice, niche separation, and density dependence.

Using a PIT detection system and two in‐stream, swim‐through antennas, we examined the movements of Arctic Grayling Thymallus arcticus through a low‐gradient (<1%), nature‐like fishpass that connected two small lakes in the Barrenlands region of northern Canada. We used an ensemble of generalized linear mixed models to evaluate whether passage events (1) were related to fish FL, water depth in the fishpass, and/or temperature in the fishpass; and (2) exhibited any diel patterns. During two seasons, passage events were not related to fish FL or fishpass water temperature; however, the probability of a passage event occurring increased with increases in fishpass depth, which likely served as a proxy for velocity and/or discharge. Most notably, 95% (n = 193/204) of Arctic Grayling passages occurred at night (1800–0559 hours) throughout our study. Although the cause(s) of this diel pattern were not examined directly, we hypothesized that it represented a response to avian predation given the shallow depth of the fishpass and given our observations of daytime avian predation events on Arctic Grayling in the littoral zones of the study lakes. Our results offer novel insights into correlates of Arctic Grayling passage through a fishpass and lay the foundation for future studies to address the hypotheses supported herein with well‐designed experiments to determine the mechanisms behind the patterns we observed. Received September 8, 2015; accepted April 7, 2016 Published online July 28, 2016

We evaluated pool use by Arctic grayling (Thymallus arcticus) in an engineered stream in the Canadian Barrenlands at the summer background flow (1.0 l/s) and at enhanced flows (9.9 l/s and 21.9 l/s) similar to those during the spring spawning period. We used an acoustic Doppler velocimeter to measure and map out point velocities (horizontal and vertical) in five study pools. The positions of adult Arctic grayling were monitored for each flow condition using visual surveys and a novel video assessment technique. Although fish mobility limited pool selection at the summer background flow, the highest use of pools by fish during enhanced flows occurred where pool designs incorporated scour holes or downstream sills to provide larger amounts of relatively deep water. Within those pools, grayling selected for locations with depths between 0.20 m and 0.30 m and near-zero vertical velocities (−0.02 m/s to 0.04 m/s). Fish selected near-zero horizontal velocities(0.00 m/s to 0.04 m/s) for resting and higher velocities (0.12 m/s to 0.20 m/s) for feeding. In contrast, grayling tended to show local avoidance of areas with horizontal velocities above 0.2 m/s or vertical velocities above 0.04 m/s. Although findings are likely site specific, our study contributes towards the development of size, depth, and velocity criteria for Arctic grayling habitat; this information can promote effective designs for habitat compensation and fish passage projects. We also present a novel video monitoring method that can be easily deployed at remote locations.