Northwest Fisheries Science Center

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Document Type: Report
Center: NWFSC
Document ID: 6513
Title: Delta and nearshore restoration for the recovery of wild Skagit River Chinook salmon:  linking estuary restoration to wild Chinook salmon populations
Author/Editor: E. M. Beamer, A. McBride, Correigh M. Greene, R. Henderson, G. Hood, K. Wolf, K. Larsen, Casey A. Rice, Kurt L. Fresh
Contributing Author: E. M. Beamer (contributing author)
Year: 2005
Institution: Appendix D in Skagit Chinook Recovery Plan. Report of the Skagit River System Cooperative. LaConner, Washington
Abstract:

In 1992 we set out on a research path to understand the role the Skagit estuary might play in recovering wild Skagit Chinook salmon.  Now, over a decade of field research has informed our understanding of Skagit Chinook salmon populations and estuarine habitat.  This document synthesizes studies of estuary habitat use, life history variation, estuary habitat loss, marine survival, and potential global warming scenarios, to predict the benefits of potential restoration projects for recovering Skagit Chinook salmon.  In summary, our research leads to the following conclusions useful for Chinook population recovery planning:

1.  All six wild Skagit Chinook salmon stocks include delta rearing and fry migrant life history types in their populations. These life history types currently rear in Skagit delta and pocket estuary habitats.

2.  Skagit delta and pocket estuary habitats are much smaller and more fragmented than historically.  Therefore, rearing opportunity of estuarine rearing Chinook salmon has been greatly reduced.  Restoration opportunities exist at both historic delta and pocket estuary sites.

3.  At contemporary Chinook salmon population levels, current delta habitat conditions are limiting the number and size of juvenile Chinook salmon rearing in delta habitat.  Otolith data indicates that delta residence is important for the success of juvenile Chinook salmon surviving later in their life cycle.  Restoration of delta habitat should increase capacity for delta rearing Chinook salmon.

4.  At contemporary Chinook salmon population levels, limitations in current delta habitat conditions are displacing juvenile Chinook salmon from delta habitat to Skagit Bay habitat and forcing a change in their life history type from delta rearing to fry migrants. Literature values show that fry migrant survival is much lower than delta rearing individuals.

5.  Some fry migrant Chinook salmon rear and take refuge in pocket estuaries.  Restoration of pocket estuary habitat can be a strategy to partially mitigate delta density dependence and improve survival of naturally occurring fry migrants.

6.  Differences in habitat connectivity influence juvenile Chinook salmon abundance in both delta and pocket estuary habitats, indicating that habitat fragmentation, in addition to habitat loss, has been detrimental to Skagit Chinook populations.  Restoration of connectivity should be a component of Skagit Chinook salmon population recovery planning.

7.  Large-scale climatic processes influence marine survival.  In the past 30 years we have observed two different climate regimes; average marine survival between regimes has varied by a factor of three.  Skagit Chinook salmon population recovery planning must consider possible shifts in marine survival and ensure population recovery is achieved under a variety of conditions, including the worst-case scenario.

Collectively, these conclusions demonstrate that wild Skagit Chinook salmon populations will benefit from estuarine habitat restoration (both delta estuary and pocket estuary habitat) and improved migration pathways within and between estuary habitats.  From these results we have developed tools to predict benefits of candidate restoration sites thus linking potential estuary restoration with Skagit Chinook Salmon recovery goals.

Notes: Complete report available from http://skagitcoop.org/documents/
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