Can the creation of new freshwater habitat demographically offset losses of Pacific salmon from chronic anthropogenic mortality?

Over 1 billion USD are devoted annually to rehabilitating freshwater habitats to improve survival for the recovery of endangered salmon populations. Mitigation often requires the creation of new habitat (e.g. habitat compensation) to offset population losses from human activities, however compensation schemes are rarely evaluated. Anadromous Pacific salmon are ecologically, culturally, and economically important in the US and Canada, and face numerous threats from climate change, over-harvesting, and degradation of freshwater habitats. Here we used a matrix population model of coho salmon (Oncorhynchus kisutch) to determine the amount of habitat compensation needed to offset mortality (2-20% per year) caused by a range of development activities. We simulated chronic mortality to three different life stages (egg, parr, smolt/adult), individually and in combination, to mimic impacts from development, and evaluated if the number of smolts produced from constructed side-channels demographically offset losses. We show that under ideal conditions, the typical size of a constructed side-channel in the Pacific Northwest (PNW) (3405 m2) is sufficient to compensate for only relatively low levels of chronic mortality to either the parr or smolt/adult stages (2-7% per year), but populations do not recover if mortality is >10% per year. When we assumed lower productivity (e.g.; 25th percentile), or imposed mortality at multiple life stages, we found that constructed channels would need to be larger (0.2-4.5 times) than if we assumed mean productivity or as compared to the typical size built in the PNW, respectively, to maintain population sizes.. We conclude that habitat compensation has the potential to mitigate chronic mortality to early life stages, but that current practices are likely not sufficient when we incorporate more realistic assumptions about productivity of constructed side-channels and cumulative effects of anthropogenic disturbances on multiple life stages.

Using Video to Evaluate Depth and Velocity Selection by Arctic Grayling (Thymallus arcticus) in Pools of an Engineered Tundra Stream

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.

Adding the “where” to the “who and what”. Considering the seascape can help the study of biodiversity and ecosystem functioning.

Whether we want to conserve, restore or enhance biodiversity, or use it to assess the environmental status of our coasts, the indissoluble link between biodiversity and ecosystem functioning is influenced by the spatial context of an ecosystem (the seascape). Using field-based research conducted in subarctic regions, we will show how the seascape can modulate species interactions which impair the habitat-forming functions of kelp. Specifically, bottom heterogeneity modulates top-down grazer control impacting the functioning of artificial structures as habitats for canopy-forming seaweeds in habitat compensation efforts. Unfortunately, coastal habitat maps from which seascape information could be obtained are often non-existant or are coarse in scale. We thus present how optical imagery-derived photomosaics can be used to map biological and geomorphological features over continuous and wide areas. Moreover, photomosaics can reveal patterns of local distribution of benthic species that can be useful when assessing biodiversity to evaluate the environmental status in coastal areas. Seascape context is thus a determining element which will improve our ability to maintain ecosystem functioning and services and inform coastal management.

Adding the “where” to the “who and what”. Considering the seascape can help the study of biodiversity and ecosystem functioning.

Whether we want to conserve, restore or enhance biodiversity, or use it to assess the environmental status of our coasts, the indissoluble link between biodiversity and ecosystem functioning is influenced by the spatial context of an ecosystem (the seascape). Using field-based research conducted in subarctic regions, we will show how the seascape can modulate species interactions which impair the habitat-forming functions of kelp. Specifically, bottom heterogeneity modulates top-down grazer control impacting the functioning of artificial structures as habitats for canopy-forming seaweeds in habitat compensation efforts. Unfortunately, coastal habitat maps from which seascape information could be obtained are often non-existant or are coarse in scale. We thus present how optical imagery-derived photomosaics can be used to map biological and geomorphological features over continuous and wide areas. Moreover, photomosaics can reveal patterns of local distribution of benthic species that can be useful when assessing biodiversity to evaluate the environmental status in coastal areas. Seascape context is thus a determining element which will improve our ability to maintain ecosystem functioning and services and inform coastal management.

Marsh and Riparian Habitat Compensation in the Fraser River Estuary: A Guide for Managers and Practitioners

A guide designed to help improve the state of habitat compensation in the Fraser River Estuary by making sound, evidence-based recommendations guided by the findings of Lievesley and Stewart (2016), Assessing Habitat Compensation and Examining Limitation to Native Plant Establishment in the Lower Fraser River Estuary. The findings from this study indicate that only one-third of sampled marsh habitat compensation projects created between 1983 and 2010 are acceptably compensating for habitat losses; and that several riparian habitat compensation projects from this same time period had significant deficiencies. These findings indicate that there is still much room for improvement in the field of habitat compensation in the Fraser River Estuary.

Stream habitat connectivity in the Canadian Arctic: an on-site approach to design and construction

We developed a successful on-site approach for design and construction of stream modifications that addressed challenging remote-site conditions of limited field data and available construction materials. Fish habitat connectivity enhancements were constructed within an Arctic headwater stream containing a naturally impassable cascade section with 13% slope, which was bypassed in a newly constructed channel at 5% slope with nature-like fishpass structures. Primary design considerations included (1) creating suitable hydraulic characteristics for fish passage in periods of high and low discharges; (2) reducing drop heights and creating unimpeded flow paths; (3) improving hydraulic complexity for a variety of stream habitats; and (4) salvaging and incorporating vegetation disturbed from construction activities into riparian and in-stream habitat structures. In high gradient reaches (2.5%–5%), we constructed boulder weirs, boulder chokes, and deflection boulders to overcome migration impediments. In medium gradient reaches (1.5–2.5%), rock ramps, boulder chokes, and deflection boulders were constructed to control hydraulic characteristics to ensure an unimpeded flow path, suitable hydraulic complexity, and resting zones. At lower gradients (<1.5%), we incorporated a softer approach using riparian vegetation and in-stream woody debris to ensure a similar quality of fish habitat as created in the higher gradient reaches. Initial hydraulic responses to the modifications indicated this reconstructed channel provided suitable hydraulic and habitat characteristics for habitat connectivity throughout the entire stream. Our findings advance understanding of headwater stream hydraulics in the Canadian Arctic and will assist in designing future stream restoration and fish habitat compensation projects on small and remote systems. This case study supports the feasibility of successfully constructing future habitat compensation projects in challenging remote environments when using an on-site, adaptive design and construction approach.

Stream modifications to enhance system connectivity for fish habitat compensation: a case study in the Barrenlands region of Canada

This study examines stream modification efforts to increase the productive capacity of an isolated system of three small lakes in the Barrenlands region of Arctic Canada by enhancing system connectivity. The lakes’ outlet streams were modified to create conditions favourable for fish passage and thereby promote migration among the lakes and the large lake into which they drain. Gabion step pools (in two streams) and a nature-like choke-and-pool structure (in one stream) were installed. Two years of post-construction hydraulics data were compared to data collected for two years prior to construction to determine the efficacy of the various stream modifications. Initial evaluations indicated unsuccessful performance of gabion step pools, so after the first year, they were retrofitted with boulders to increase flow depth, restrict discharge, improve flow duration, and create unimpeded connections rather than sudden drops. Variation of lake levels and duration, variability, and depth of stream flow indicated that outlet geometry and lake catchment area should be important considerations when enhancing connectivity for fish migration in ephemeral systems. A narrow, rectangular cross-section was deemed effective for increasing flow depth while decreasing discharge, resulting in increased duration of flows. Catchment area was an effective indicator of a headwater lake’s potential response to connectivity enhancements. Smaller catchments may provide inadequate runoff to sustain minimum storage requirements for enhanced connectivity. Our findings should advance the knowledge of headwater system hydraulics in the Barrenlands and assist in designing future fish habitat compensation projects on similar systems.