King County Executive Dow Constantine on Monday called for a six-month moratorium on new Atlantic fish farming facilities along unincorporated King County shoreline.

While there currently are not any net pen operations in the waters off Vashon and the county has not heard of any specific plans to begin the operations, Constantine’s announcement was preemptive, Alex Fryer, director of communications for Constantine’s office said Monday. In a news release, Constantine mentioned the August incident when 300,000 non-native Atlantic salmon spilled into the Salish Sea north of Anacortes as reason for the ban. More than 100,000 were never caught.

“Atlantic salmon don’t belong here,” Constantine said in the statement. “Beyond a six-month moratorium, we need to ensure these operations can never again pose a threat to indigenous salmon already struggling to survive.”

Legislation to put the ban in place was given to the King County Council Monday. Indian tribes including the Muckleshoot and Suquamish tribes reviewed and approved the proposed moratorium to ensure it did not interfere with their local fisheries and treaty rights.

King County rivers are home to seven native salmon species, including chinook, steelhead, and bull trout populations that are protected by the Endangered Species Act. Puget Sound is where these and other salmon species spend much of their lives, feeding for a year or more, before returning to their home streams to spawn.

The salmon pen ban will enable King County to review and strengthen its shoreline regulations to eliminate the risk of harm from non-native salmon farming to native salmon runs and sensitive shorelines.