Habitat Restoration in the Nechako River - Spawning Reach
Altering the natural flow and sediment regimes of a river may cause significant physical and ecological change within the ecosystem. One common effect of flow-regulation by dams is a reduced ability to mobilize and transport sediment. As sand and fine gravels increasingly deposit on the riverbed, the gravel substrate that is used by early life stage sturgeon may become covered by sand and fine sediment and pore spaces between larger gravels and cobbles infill. Larval white sturgeon have been shown to preferentially hide within these pore spaces of gravel immediately after hatching, providing them with several survival advantages such as increased growth and reduced predation.
The infilling of gravel by sand within the spawning reach in Vanderhoof is continuous. Habitat restoration methods to clean and restore the substrate are advancing. For an excellent overview of the most current work - watch this video:
NWSRI Habitat Restoration Video (2025)
The spawning reach is divided into three 'patches' - Upper, Middle and Lower, and over the years, a number of experiments and monitoring have occurred within the patches.
2011 - Substrate Placement
In 2011, 2,100 cubic metres of gravel of cleaned and sorted gravel substrate were placed on the bed of the Nechako River at the white sturgeon spawning grounds near Vanderhoof, BC (Lower & Middle patches). Biological and physical monitoring programs of the gravel pads have been conducted each year since placement.
Using underwater cameras and other sampling methods, the three patches were monitored for sediment transportation over the next several years. It was found that there was moderate transportation of sediments in the Upper patch, and little to no transportation was recorded in the Middle and Lower patches, meaning that the substrate that was added to the Middle and Lower patches remained in place.
EGG RELEASE 2011- After the placement, hatchery raised eggs were released over the newly placed spawning gravel. Subsequently, a recruitment pulse was observed in 2011 as well.
2014-2017 - Sediment Transportation Studies
Understanding the placement and movement of sediment transported through and deposited within the spawning reach has implications on further research and mitigation measures to improve the potential effectiveness of the spawning reach. The main findings included:
- The bedload movement was estimated to be 10 times less than previous estimates.
- Transport of sediment was higher at the observed river flow rate at the site above the spawning reach compared to below.
- Visual evidence of infilling in the lower patch of the spawning reach. Yet there were visibly suitable habitat for spawning within the study area.
Recommendations from this included:
- Developing a sediment cleaning plan to physically clear fine sediment from gravel beds in the lower patch of the spawning area.
- Continue to take underwater visual recordings of the lower patch to determine spawning quality.
2016 & 2020 - Substrate Cleaning
Based on recommendations from the sediment transportation work, in 2016 a spider excavator was deployed to clean the spawning gravel within the Lower patch of the spawning reach. The machine picked up the substrate and gently shook it back into the river. The fine sediments are then carried by the current downstream, resulting in ‘cleaner’ gravel. In 2020, substring cleaning occurred in the Lower patch in the fall.
EGG RELEASE 2016 - After cleaning, hatchery raised eggs were released over the newly cleaned spawning gravels.
EGG RELEASE 2021 - The following spring, after the substrate cleaning in the fall of 2020, eggs were released over the Lower patch.
A constraint of this work however is how to maintain substrate quality when there is continual sand input into the spawning reach.
2022-2023 - Egg and Larval Experiments
Over two summers, researchers conducted lab and in-situ experiments to determine effective egg dispersal monitoring techniques, as well as larval settlement success over different substrates and velocities. Both studies help inform habitat restoration work moving forward, as the studies found that:
- Fewer eggs were captured on egg mats in the cleaned channel due to higher retention in the crevices between gravel particles.
- Substrate composition did not statistically influence the proportion of larvae that settled. Larvae settled equally well in gravel compared to gravel covered with a layer of cobble.
2023 - Tubescreen Cleaning Method Test
Within a side channel of the, researchers developed and tested a 'tubescreen' - a metal filtering device to be towed behind a boat that sorts substrate. The concept is to drag the device on the bottom of the river to lift the substrate, and reorganize the substrate with fines falling first, then covered by grails then cobbles. The method did show improvements to substrate quality.
2025 - Sled Substrate Cleaning
Using lessons learned in the tubescreen cleaning tests, the NWSRI Technical Working Group team conducted a full-scale cleaning operation in the Lower patch of the spawning reach using the tubescreen, as well as a larger 'sled'. The ultimate goal continues to be to increase the chance of survival of wild spawned eggs and larvae.
Using the specialized equipment crews carefully scraped the riverbed, lifting the substrate at its location. The work occurred weeks ahead of sturgeon spawning in the spring. A portion of the Lower patch was cleaned. Monitoring of the substrate change was done using freeze core sampling as well as video monitoring.
EGG RELEASE 2025 - After cleaning, hatchery raised eggs were released over the newly cleaned spawning gravels.