Near shore salmon habitat in Chignik, southwest of Kodiak on the Alaska Peninsula, is slowly disappearing. One researcher out of Seattle, Washington looked into why.
Alaska Fisheries Science Center biologist Mark Zimmermann was studying maps of ocean depth from the 1920s and 1990s and noticed a big difference along the coastline.
“In Chignik, there were many neighboring maps that all reported the same thing. It was all getting shallower. And that was really unusual.”
Zimmermann wanted to find out why. After some investigation, he learned that layers of volcanic ash were shallowing the sea floor.
“From what we can tell, it’s just covering a lot of the landscape in the Chignik area, and it’s been there for, in some cases, thousands of years since very large caldera forming eruptions occurred, and we think it is just eroding from the hillsides with wind and rain and snowfall and trickling down through the watersheds into the bays.”
He found that ash was encroaching on salmon habitat, especially in Mud Bay and Chignik Lagoon, where eelgrass is abundant.
“And we think that the roots of the eelgrass are serving to help entrap the sediment and those bays are seeing more sedimentation than the other bays. There is so much sedimentation that these areas are becoming too shallow for the regular fish habitat use.”
He says the rate of change is slow, but it could affect how salmon reproduce in the long-term.