Lower Cowlitz River Monitoring and Evaluation, 2013

For more than half a century the Cowlitz River has been divided by a series of three dams, constructed in 1963 to 1968 to support hydroelectric development in the basin. These dams greatly reduced natural salmon and steelhead populations, and large hatcheries were constructed and operated to mitigate this impact. Currently, an extensive reintroduction program in the Cowlitz River is underway to restore the anadromous migration corridor between the upper and lower Cowlitz River basins. Hatchery programs have been modified to support this reintroduction while continuing to support fisheries in the lower Cowlitz River. Successful recovery of natural salmonid populations in the Cowlitz River will require minimizing the impacts of the hatchery programs on lower Cowlitz River populations. This report describes the efforts to implement the first year of the lower Cowlitz River Monitoring and Evaluation Plan. The focus of this effort is to estimate spawner abundance and composition, hatchery returns and composition, and Cowlitz River fishery impacts on lower Cowlitz River populations of winter steelhead, coho salmon and spring and fall Chinook salmon.

Mark-recapture estimates of steelhead spawner abundance for spawn year 2013 were made for Delameter and Olequa creeks. The mark-recapture estimate of steelhead abundance above the weir locations was 86 fish (CV = 9.5%) for Delameter Creek and 133 fish (CV = 15.9%) for Olequa Creek. Mark recapture estimates of coho spawner abundance for spawn year 2013 were made for Ostrander, Delameter, and Olequa creeks. The mark-recapture estimate of coho spawner abundance above the weir locations was 109 fish (CV = 16.0%) on Ostrander Creek, 174 fish (CV = 15.1%) on Delameter Creek and 250 fish (CV = 20.1%) on Olequa Creek. In 2013, the estimation method for total tributary spawner abundance was similar for both steelhead and coho. This method used mark-recapture estimates above weir locations and the modeled spawning distribution for each species.

The total number of steelhead spawners in lower Cowlitz River tributaries (excluding Toutle and Coweeman rivers) for spawn year 2013 was estimated to be 559 (508 natural-origin and 51 hatchery-origin) with a proportion of hatchery origin spawners (pHOS) of 0% to 13.9% above weirs and 9.2% for non-weir tributaries. The total number of adult coho spawners in lower Cowlitz River tributaries (excluding Toutle and Coweeman rivers) for spawn year 2013 was estimated to be 1,694 (1,565 natural-origin and 20 hatchery-origin) with a pHOS of 0% above weirs and 1.7% in non-weir tributaries.

The estimation method for spring and fall Chinook salmon for spawn year 2013 was based on an expansion of peak aerial redd counts and age composition from carcass recoveries. The abundance of spring Chinook salmon spawners was estimated to be 960 spawners (pHOS = 89%). The abundance of fall Chinook salmon spawners was estimated to be 4,436 spawners (pHOS = 19%).

Estimated returns of natural-origin (NOR) and hatchery-origin (HOR) adult steelhead, coho salmon, spring Chinook salmon, and fall Chinook salmon returning to the lower Cowlitz River in 2013 are summarized in the table below. These are the best available estimates with the caveat that the methodologies to minimize bias and include precision are still being derived. Integrated (I) and Segregated (S) hatchery programs are noted. Table does not include NOR returns to the Tilton or upper Cowlitz River. The table is partially completed because the lower Cowlitz River Monitoring & Evaluation Plan was only partially implemented in 2013. More complete implementation of the M&E Plan is underway for 2014.