May 11, 2020

Salmonids Migrate Up Seymour River 5 Years After Slide

Seymour Slide: 2019 Sees First Success for Returning Sea-Run Salmonids After Five Years of Hard Work

The Seymour is one of only two Burrard Inlet streams to support both a summer and winter run of steelhead. Its location makes it popular for anglers and non-anglers alike. However, anglers familiar with Vancouver’s North Shore will undoubtedly recall the devastating rockslide that dumped 50,000 cubic metres of boulders and rubble into the Seymour River on December 7, 2014. The Seymour system already suffers from the various challenges of an urban stream, as well as having been dammed since the 1920s to provide a clean drinking water supply. Many thought this latest catastrophe could be the final nail in the coffin for its salmon and steelhead runs.


The Seymour watershed area above the rockslide and below the Seymour Falls Dam. | Reece Fowler, Seymour Salmonid Society. 

Prior to the slide, salmon and steelhead returned to the river annually. This has been in large part due to the committed efforts of the Seymour Salmonid Society, which maintains the on-site hatchery that produces coho, summer and winter steelhead, chum, and pink salmon juveniles for release each year. With no fishway at the dam, adult fish are not able to migrate beyond it without assistance. This group is also coordinating efforts to get fish above the dam to the upper watershed, where significant stretches of spawning and rearing habitat exist.


Assessing passage past the giant ‘House Rock’, which is part of the rockslide. | Reece Fowler, Seymour Salmonid Society.

Until the rockslide, coho and steelhead (both summer and winter) were able to access portions of the river below the dam to spawn. In 2015, though, a tagging study confirmed that no adult salmon or steelhead could move upstream beyond the slide. Given the rockslide’s location, spawning options for coho and steelhead were so severely restricted that, if mitigation weren’t undertaken, these populations would likely become unviable over the next couple of generations.

As the chinook population has always been very small, and since chum and pink salmon are generally limited to spawning locations below the rockslide, the impacts to these species are considerably less. Unfortunately, to reduce the blockage’s impacts on all salmonids, the entire river has been closed to fishing since the slide occurred. Restoration of fish passage was determined essential to maintain the ecological integrity of this river as a priority salmonid-bearing system in the Lower Mainland.

Starting in 2016, multiple partners, including the Freshwater Fisheries Society of BC, contributed significant funds to the Seymour Salmonid Society to coordinate the restoration of the salmonid migratory channel at the rockslide’s location for both adults moving upstream, and juveniles moving downstream. This has been no small feat. Removal of debris had to be done in a controlled way to retain bank stability, and to ensure that debris removal in one section did not subsequently create barriers downstream. Water flow levels also had to be considered, since passage through the slide area is easier for fish during certain flow conditions.


Site of the rockslide on the Seymour River. | Reece Fowler, Seymour Salmonid Society.

So far, rock drilling and controlled blasting have taken place annually during summertime low flows to reduce the river gradient at critical locations, and to fill in large spaces in order to provide a usable channel for fish. Once these activities are completed, hydraulic engineers must wait until after the next springtime freshet (when material is mobilized by large volumes of water) to assess their effectiveness in terms of channel formation.


A summer steelhead captured in 2019 as part of the ongoing hatchery broodstock program on the Seymour. | Reece Fowler, Seymour Salmonid Society.

However, the true test is observing successful fish movement unassisted by humans. Radio-tagging out-migrating coho smolts in 2017 and 2018 confirmed that juvenile salmon could successfully move downstream past the rockslide, but it wasn’t until 2019 that tagged adult coho were documented to have successfully navigated upstream of this location. A combination of tagging and observational data confirmed that three of the radio-tagged coho adults had made it to upstream waters in the fall of 2019. In addition, non-tagged steelhead were also observed above the rockslide in 2019. Initial estimates associated with carcass recovery counts, and the operculum (gill cover) tagging program of transported fish, indicated that 300-400 salmon made it upstream on their own in 2019, which was at least comparable to the number that were trapped downstream and trucked for release above the slide.


Fish jumping upstream at rockslide. | Georgia Dixon, BCIT.

To complement these efforts in 2019, the Seymour Salmonid Society also moved 32 coho pairs upstream to the section of river above the dam. And for the first time in 90 years, adult coho had the opportunity to spawn there naturally.


Coho salmon were collected and moved upstream. | Reece Fowler, Seymour Salmonid Society.


River seining salmon in preparation for moving them to the upper river to access spawning grounds. | Reece Fowler, Seymour Salmonid Society.

These are positive signs that efforts to restore passage through the Seymour rockslide are working. In 2020, more rock breaking and moving work is planned during the summer low flows.

The Society is pleased to have contributed funds to this multi-partner initiative over the past four years.  We would also like to acknowledge the tireless work of the Seymour Salmonid Society in coordinating efforts to have salmon and steelhead once again move naturally upstream beyond the rockslide.


Large male coho caught in the Seymour River. | Brian Ha, Capilano Hatchery.

For further information please contact:

Mike Willcox (Ministry of Forests, Lands, Natural Resource Operations and Rural Development)
Reece Fowler (Seymour Salmonid Society)

Interactive Map: Watch the Seymour Steelhead Ocean Migration 

Kintama Research Services has conducted marine tagging work to better understand ocean migration and survival of juvenile salmonids. Interested readers can study an interactive map of 229 Seymour summer-run steelhead that were acoustically tagged in 2015, from the time of release starting May 19, to September 14 when no further movement past receivers was detected.



Author: Sue Pollard, Freshwater Fisheries Society of BC
Images: Reece Fowler, Seymour Salmonid Society; Georgia Dixon, BCIT; Sam Pritchard, Seymour Salmonid Society; Brian Ha, Capilano Hatchery.