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The Elwha Nearshore’s Ecological Function and Dam Removal…

The rapid changes to the Elwha nearshore are both exciting and inspiring. The Coastal Watershed Institute has been monitoring the ecological function of the Elwha nearshore for over a decade, including both pre-dam removal and dam removal timelines. We presented some of our preliminary observations of nearshore response to dam removal at the Salish Sea Conference held in Seattle April 20 – May 2 2014. Dam removal is still in full swing so everything is very much in flux both physically and ecologically. With that caveat, the presentation summarized highlights of our observations of juvenile fish use of the Elwha estuary. In the spirit of the conference’s emphasis on shared ecosystem responsibility, this post includes much of the material covered in the presentation.

The Elwha nearshore is a part of the Strait of Juan de Fuca, the major conduit between inland and coastal ecosystems. Legislation from 1992 cleared the way for dam removal on the Elwha River -the enabling legislation stipulated the restoration of the Elwha ecosystem-which includes nearshore….

Will dam removal make a difference for native salmon? The answer is a resounding yes. A comparasion of successful spawning adult salmon numbers after dams were installed (the 2005 data) and an estimate of pre dam spawning numbers reveal dramatic-but not unexpected-declines in fish use which are due to dams.

Note that prior to dams, chum and pink were a dominant salmon in the Elwha system. After dams were installed? Their estimated numbers slipped to teetering on extinction for this river.

Prior to the dam removals, the Elwha nearshore has tbeen severely sediment starved over the last 100 years, largely driven by anthropogenic changes of shoreline armoring, in-river dams, and lower river alterations. In contrast, the flood of sediment since the dam removals began in 2011 has actually, as of March 2014, contributed over 100 acres of new estuary and intertidal habitat.

And we are only just beginning. Dam removals have also reactivated complex and critically important nearshore physical and ecological processes. In this volatile meeting of river and marine hydrodynamics we have been lucky enough to conduct a study of fish abundance since 2007.

Study: Fish use as metric for ecological function

This paper presented an overview of results to date of CWI’s ongoing study to define how nearshore ecological function responds to dam removal sediment delivery through three time phases: 1. Pre-dam removal; 2. Dam removal; 3. Post-dam removal

We define basic ecological function using fish metrics. We are currently in the dam removal phase of the study, so results provided are for pre-dam removal and dam removal phases. Monthly sampling since 2007 gives us a clear picture of the changes over time to the nearshore. In 2013 we added sampling sites as the estuary expanded. Salt Creek is used as a comparative site.

Sediment delivery has just begun. Numbers change daily, but somewhere between 20-60 percent of the 16 million cubic meters (what an astounding number!) of sediment predicted to be delivered to the nearshore has arrived. Physically, restoration has just begun.

Ecologically?

While the story is still unfolding-remember dam removal is not yet complete and sediment is just starting to arrive to the nearshore-we’re seeing the following changes in the Elwha estuary. We attribute these changes with dam removal as we are not seeing these changes in the comparative Salt Creek area.

Of particular interest in our observations is the first documented appearance of eulachon in the Elwha estuary. Eulachon are a culturally and federally listed important species. If we look at basic ecological metrics as an indicator of change in the Elwha estuary relative to our comparative area this is what we see to date. The red line indicates the beginning of dam removal.

In a nutshell?

Species Richness is highly variable in the nearshore, and defined by month. Species Richness in the Elwha estuary has not changed significantly since dam removal began, and is not significantly different than that of the comparative area.

We may be seeing some response in Chinook and coho use of the Elwha estuary-hatchery releases make it VERY hard to decipher….

Observations of our chum data are very intriguing. While overall abundance appears to be about the same, when, and the size of, juvenile chum are using the Elwha estuary appears to be changing.

Conclusions

It is vital to stress that these results are preliminary and will undoubtedly change as the Elwha nearshore continues to restore. We will continue to work on these elements in more detail for the upcoming post dam removal phase. Our informal, preliminary observations to date:

Overall, ecological function of the Elwha estuary is functioning at pre-dam removal level thru the dam removal phase. New estuary sites functioning at same ecological level for fish as original Elwha sites. As soon as the estuary habitat is available juvenile salmon are using it.

Elwha nearshore estuary habitat is changing rapidly: both estuary and lower river habitat are expanding. Both changes are reflected in fish use as the estuary and lower river grow.

Chum use of the estuary may be more complex than initially understood – juvenile appear to be leaving the estuary earlier, and smaller than prior to dam removal. We’ll assess this in more detail once dam removal is over.
Hatchery releases currently occur at the peak of juvenile chum use of the Elwha estuary. Given the importance of the estuary for restoring chum, and the historic importance of chum to the watershed, chum should be considered in much more detail when considering adaptive managment options for the watershed. We’ll assess this in the near future after 2014 (dam removal) outmigration season and project phase is over.

Thank you to:

CWI volunteer extraordinaire Anne Gough contributed significantly to this blog!

And for some fun footage of juvenile salmon use of the nearshore see our humble video:

https://vimeo.com/100600510