PUGET SOUND, Wash. -- King County is pulling up creatures from the depths of Puget Sound in hopes that what they learn from the bottom of the food chain can help predict the future success of salmon runs -- and in turn -- the endangered southern resident orcas that eat them.
Twice a month every month, King County Environmental Laboratory takes out the SoundGuardian boat for its marine ambient survey, which has about 20 stations around the Sound. At each station, scientists cast over the edge of the boat an instrument they call CTD, which stands for conductivity, temperature and depth.
It's a survey they've been doing for decades. There's a lot to learn under the surface of Puget Sound and what they find in the darkness sheds light on the health of the ecosystem. But a step the lab added about five years ago is further expanding their knowledge.
On one day on the water with the lab, we stop at Carkeek Park, Point Jefferson, Point Wells, West Point, Elliott Bay and the Duwamish River.
Environmental scientist Bob Kruger drives the CTD to the depths of each location, up to 280 meters. In real time, the CTD measures temperature, salinity, dissolved oxygen, chlorophyll and photosynthetic radiation. It also has several canisters they can trip to capture water samples at certain depths and bring to the surface to bottle for lab testing.
Kruger looks at a laptop screen, identifying the real-time chlorophyll levels as the CTD goes down.
"That's the maximum in this water column," he said, pointing at a peak in the chart. "We're interested in that so we're going to take a sample on the way up."
When the CTD hits the deck, two scientists settle into the humdrum routine, filtering and sorting samples that will get sent back to the lab. They do this at every station.
Going the extra step
About five years ago, King County added another step to test for zooplankton, the food source for forage fish and young salmon.
At one station, they sent a vertical ring net 200 meters down and, using the crane, slowly pulled it back up through the water column. The fine mesh catches all of the creatures in that location.
"This is what we call the big reveal," Houston Flores said.
They sprayed the contents of the net into a sieve and placed the zooplankton and phytoplankton samples into a bucket to take a look. A lot of critters swam around, from jellies to crab larvae.
"Oh, those salmon are smacking their lips!" said Kimberle Stark, Water Quality Planner for King County Department of Natural Resources.
The food web is pretty simple. Zooplankton eat the phytoplankton, forage fish and young salmon eat the zooplankton and the endangered southern resident orcas eat the salmon once they're grown.
But for so long, there has been gaps in what we know about the health of the food web.
"The whole food web, from phytoplankton and zooplankton have not been particularly well studied just because they're really hard to sample," Stark said.
How it helps
Chlorophyll levels are indicators of the presence of phytoplankton. By knowing when during the year chlorophyll peaks and when zooplankton are at its highest levels, the science King County is compiling could possibly tell hatcheries the optimum time to release young chinook salmon to give them the greatest chance of survival.
By timing hatchery releases with the salmon's food source, they can increase chances of the juveniles putting on more weight and growth before reaching the ocean.
"Instead of just saying, 'Hey, I'm pretty sure this is going on,' they can say, 'I know this is happening because this data proves it,'" Kruger said.
He goes on: "I don't think just zooplankton is going to answer any big questions. But we can look at a lot of different causes of the population decline of chinook salmon and this is just one piece of the puzzle."