Beamer, E. and Wolf, K., 2016. The influence of a naturally formed distributary channel on the distribution of juvenile Chinook salmon within the Skagit tidal delta. Skagit River System Cooperative, La Conner, WA. pp. 30.

In 2006 a new distributary channel began to form within the North Fork region of the Skagit tidal delta. This created a new fish migration pathway within and through the delta, potentially changing the distribution of juvenile Chinook rearing in the delta and influencing juvenile Chinook use of existing habitat and future restored habitat. This study used existing fish data to test whether the formation of a new distributary has changed the distribution of juvenile Chinook salmon within the Skagit tidal delta.
The long-term monitoring dataset provides an opportunity to retrospectively test spatially explicit hypotheses for juvenile Chinook densities before and after the new distributary formed at six sites in the Skagit tidal delta and Skagit Bay nearshore. We found the new distributary is not a viable pathway to move juvenile Chinook from the North Fork Skagit River to Fir Island’s bayfront marsh habitat. Instead, juvenile Chinook that take the new distributary pathway are more likely to be exported to Skagit Bay nearshore than are juvenile Chinook taking the pathway along the North Fork Skagit River.
The new distributary has changed water flow and sediment deposition patterns within the North Fork tidal delta, which are further influenced by large scale processes also acting on tidal delta conditions, such as sea level rise and sediment inputs from the Skagit River. We identify areas within the North Fork tidal delta where habitat changes are rapidly occurring, including a) areas where distributary channel habitat is filling and changing to marsh / blind tidal channel habitat, and b) areas with less certain habitat change trajectories.
We recommend continued monitoring of fish and habitat in the Skagit tidal delta. The formation of the new distributary is a proxy for restoration actions being proposed in the Skagit (e.g., Fir Island Cross-Island Connector in the Skagit Chinook Recovery Plan) and other Puget Sound estuaries. It will be important to document how habitat in the North Fork tidal delta forms because of the new distributary and the surrounding larger scale processes, and how juvenile Chinook respond to changes.