The Muckleshoot Indian Tribe is taking a close look at the gravel in the Green River to see if it’s causing low runs of naturally spawning chinook.

“Each year we see a smaller population of naturally produced chinook leave the Green River,” said Martin Fox, habitat biologist for the Muckleshoot Tribe. “We think the low runs might have something to do with low quality gravel throughout the river.”

Gravel is important to chinook and other salmon because they spend the early part of their life cycle living in it. Returning adult salmon build eggs nests – or redds – in the gravel. When those eggs hatch, the baby fish can live in the gravel for weeks before emerging.

“Too much fine sediment, like from a landslide, can hurt salmon runs even before they have a chance to leave for the ocean,” Fox said.

Just over 3 percent of chinook that are born in the Green River survive to make it to the ocean, compared to more than 10 percent in both the nearby Cedar and Skagit rivers. This is down from more than 7 percent over a decade ago.

“We know that there is something happening on the Green, and it likely has to do with declining salmon habitat quality and quantity,” Fox said.

The tribe is studying three stretches in the river. The first, in the high, undeveloped watershed, should give the researchers an idea of what natural gravel conditions look like. Two more in the lower Green River watershed are above and below a landslide.

The EPA’s National Estuary Program contributed funding to the research.

“By taking a look at conditions on either side of the slide, we can see what kind of changes it’s having on the habitat in the river,” Fox said. “The only way we can restore strong runs of salmon throughout the region is by restoring and protecting their habitat.”