Decades upon decades of logging have made Canada into the world’s second-largest exporter of wood products. The price of such productivity became apparent in the late 20th century, when logging led to environmental damage that prompted Canada’s Department of Fisheries and Oceans to conduct a four-year restoration project in the upper Chilliwack River Watershed.
“The watershed in the study area was extensively logged during the 20th century, which increased landslide frequency and river bank instability and reduced large wood debris in fish habitat,” said Matt Foy, restoration biologist at DFO.
Foy is a co-author on a study published in the Canadian Journal of Fisheries and Aquatic Sciences which examines the effectiveness of the Forest Renewal Project that took place between 1996 and 2000. Focusing on coho salmon productivity, the study is among the first of its kind to evaluate restoration outcomes on a watershed scale.
“The restoration work increased floodplain off-channel habitat along the Chilliwack River valley,” Foy said. “Off-channel habitat is critical for juvenile coho salmon survival, particularly during the winter flood period.”
The researchers wanted to test whether the project effectively raised wild coho salmon productivity at a rate and cost comparable to hatchery production. To do so, they needed to estimate coho smolt population in the upper Chilliwack River Watershed, and the proportion of that population originating from the restored off-channel waterways.
Two years after the Forest Renewal Program wrapped up, the researchers set up traps throughout the Chilliwack River system to capture coho smolts during their spring migration. Captured smolts were marked and released, and in many cases, recaught at a downstream rotary-screw trap.
“It was challenging to operate a trap in the Chilliwack River, a large, steep, boulder-bedded mountain stream,” Foy said. “Especially during the latter timing periods when the high-level snow melt got underway.” All the sites, he noted, were located in forests, which posed a number of other minor challenges for the researchers.
Comparing data from the trapping project with area-based models built from previous studies, the researchers found that restoration improved coho smolt production. Furthermore, production in the most cost-effective restoration sites was comparable to average hatchery production costs. This is good news for future restoration projects, for which funding can often hinge upon proof of fiscal efficiency.
“The study confirmed that floodplain restoration is a viable tool for recovering wild coho productivity in rivers degraded by human activities such as logging,” Foy said. He called the findings “encouraging due to the scale and scope of the works.”