SOURCE: Seattle Weekly
DATE: January 31, 2019
SNIP: There’s little good news these days for salmon in the Lake Washington watershed, and new information from researchers paints an even bleaker future for some of Washington state’s most cherished animals.
The number of kokanee salmon returning to spawn in the tributaries of Lake Sammamish was low again this year, prompting King County to start looking at ways to preserve this freshwater species. On top of this, local sockeye species that migrate to the Pacific Ocean hit record low numbers last year because an unknown disease, or combination of diseases, is wiping out the adult salmon when they return to Lake Washington.
In Lake Sammamish, around 100 kokanee returned to spawn this year, significantly higher than the 19 seen last year, but still much lower than levels that would indicate a healthy population. King County environmental affairs officer David St. John said the low number of returning fish provides evidence for their hypothesis that a lake condition known as “the squeeze” is killing the fish.
This year’s returns provide more evidence that Lake Sammamish is in some years an inhospitable place for young fish, especially during the hot summers of 2014–16. During these years, the heat appears to have driven the young, cool-water-loving fish deeper into the lake into zones with inadequate oxygen to support them, ultimately killing them. Toward the bottom of the lake are decomposing leaves, plant matter and animals, which all lower oxygen levels. During relatively favorable years for the fish, they can dive deeper into the lake to find cooler water without being pushed into oxygen-scarce zones, but during hot summers, this habitable zone often disappears.
Other trends, specifically among Lake Washington sockeye, are even more troubling. Aaron Bosworth, a biologist with the Washington Department of Fish and Wildlife, said sockeye are dying en masse in Lake Washington from disease — a phenomenon that has increased over the past five years, during which researchers saw three of the lowest returns on record. The 2018 season was the worst ever, with only 3,500 sockeye spawning in the Lake Washington system. The previous low point was 7,000. A healthy spawning count would be more than 100,000.
Too-warm water, loss of habitat, and higher levels of CO2 in the water could all be to blame.