Octopus Marine Ecology Centre







Survey of habitats, potential food, and remediation requirements in juvenile chinook nursery areas of the Cowichan Estuary.

The Cowichan Estuary, while not a salmon-spawning habitat, is a critical and important environment for the rearing and feeding of juvenile chinook and chum, and perhaps coho salmon.

The chinook project worked broadly to:

  • survey the edges of the estuary and some areas of the mudflats to assess habitat suitability for chinook juveniles.

  • determine what if any rehabilitation is needed to improve habitat suitability.

  • develop an awareness program

1. Habitat Survey

In the Cowichan, as elsewhere, chinook smolts are scattered along the marsh edges at the highest point reached by the tide. They then retreat into tidal channels and creeks, which retain water as the tide retreats. The juvenile chinook occurs in the estuary from late March to early September, typically peaking in July and August. Populations dwindle considerably in September.

Due to delays in obtaining project funding, we were unable to start until early October. We managed to complete most of our fieldwork before the rains set in and counted our blessings for so many beautiful days. We were concerned for the change in seasons and particularly the change in chemical and physical characteristics of the estuary once the rains started.

Approximately 99% of the accessible estuary edges have been surveyed, including reclaimed marshes and shorelines, as well as impacted shorelines and mudflats at 32 Centres over a distance of 1900 meters. . The habitat survey was conducted on 0.2km sectors where possible. Each Centre contained one to four subCentres or transects. Shoreline transect protocols followed those developed by the Marine Ecology Centre over the past 8 years. Substrate (bottom) and epibenthic (above bottom) samples were taken where possible at each of the 95 intertidal sites and at 7 subtidal sites. The samples were taken at tide levels ranging from just below 2.5 meters up to 4.5 meters, above sea level. Specifics as to the type of substrate, plant and animal life were recorded on data sheets and a series of photos were taken at each transect. We also assessed each Centre transect for possible future habitat rehabilitation, if any was required.

Surveyor, David Tattam.

Mudflat sample site.

The goal of this project was to assess the suitability of various habitats for certain food items of juvenile chinook. It is recognized that seasonal, tidal, and other factors disallow any quantative assessment and further that sampling techniques are not necessarily comparable to the mechanisms used by chinook juveniles to locate and consume prey.

Field and lab technicians (left to right): Barbera Benoit, David Tatam and Margaret Walker.

David Tattam and project manager Jackie Hendrix.

Fifty samples each about 6 cm3 (6 cm 2 x 1 cm deep) were analyzed for potential chinook juvenile prey items (meiofauna). These samples ranged from the subtidal to the upper intertidal areas of the estuary. Animals larger than 50 Ám were counted. Counts ranged from 5 to 4,372 individuals per sample.

Species were identified to broad taxonomic category (e.g., nematodes (round worms) copepods (bullet shrimp), ostracods (clam shrimp), etc.)

2. Assessment for potential habitat rehabilitation

There are some areas of the estuary that have potential for remediation

Examples of potential rehabilitation:

  • Dykes could be breached

  • Salt marshes could be re-channeled to allow for better water flow in and out of the marsh

  • Vegetate or re-vegetate certain areas

  • Remove rip rap

  • Remove land fill

Downstream deposits from estuary land fill.

Photo of rip rap.

Any habitat rehabilitation in the estuary requires approval under the CEEMP. Our goal was to assess juvenile chinook nursery habitat for potential rehabilitation with a view toward obtaining the necessary approvals and permits for implementation in the future.

3. Continuing awareness program

Murals painted by two grade 12 students are displayed at the Entrance to the Marine Ecology Centre. One depicts the life cycle of Chinook Salmon from birth in the Cowichan River to the open sea and the return to the Cowichan to breed. The other displays examples of marine life in the estuary habitat with emphasis on food sources for Chinook juveniles.

Chinook Salmon Life Cycle by Jenny Olsen

Estuary habitat by Heather Jones.