Lower Chehalis River and Surge Plain Fish Use Assessment
Lower Mainstem Chehalis River, Porter to Montesano
April 2014 (sampling through late July, 2014)
During the three sampling sessions we caught over 16,000 fish, consisting of 21 different species. This included three species of salmon (chum, coho, and Chinook salmon), as well as several rainbow trout/steelhead and cutthroat. Salmon made up a relatively small portion of the total catch (15%); however, the composition of the fish assemblage changed dramatically between April and July. In April, salmon accounted for about 63% of all fish (primarily Chinook salmon), by June and July, salmon comprised less than 3% of the catch. The increased abundance of stickleback (56% of total catch), pikeminnow (8%), peamouth, red-sided shiner and juvenile starry flounder coincided with warmer water temperatures and lower river flows.
Poor floodplain conditions exist in the stretches upstream of Montesano and between the Satsop confluence and Elma due to bank armoring and channelization. Upstream of Elma, the mainstem has both spawning and rearing habitat for salmon, although the mainstem spawning habitat is used mostly by Chinook salmon. Coho salmon and steelhead trout use the mainstem for transportation to spawning areas, and also rear in the sloughs and off-channel habitats. Our research has specific implications for salmon recovery planning and restoration actions in the lower Chehalis River and Surge Plain. Juvenile salmon utilize the lower Chehalis River and Surge Plain extensively, with salmon caught at all the sample sites. Survival during this early period of their life-cycle is critical for the overall success of their respective populations.
The Lower Chehalis River and Surge Plain Fish Use Assessment was developed as a pilot study. The primary goals were to anticipate the location and extent of the future Surge Plain and to identify the key habitat areas utilized by juvenile salmon and other fishes. The project had four specific objectives at the outset:
- Estimate the future head of tidal intrusion and map the habitats of the lower river using 2013 LiDAR data. (Accomplished in July, 2014)
- Determine the abundance, distribution, emigration timing and habitat preferences of juvenile salmonids in the Surge Plain and lower Chehalis River. Meeting this objective also establishes the presence of these fish at locations in the lower river, a prerequisite for land acquisition for conservation or conservation easements.
- Understand which physical variables (flow rate, dissolved oxygen, temperature, salinity) best predict the distribution of Chinook, coho, and chum salmon, and which habitat types are of the highest priority.
- Integrate this knowledge into the Grays Harbor Estuary Salmonid Conservation Plan, which identifies specific restoration and conservation opportunities in the estuary, Surge Plain and lower Chehalis River.
Todd Sandell, James Fletcher, Andrew McAninch
The Rose Foundation
Rose Foundation, Grays Harbor county LE, and Grays Harbor Audubon