The Mariners designated Ervin for assignment Wednesday, Shannon Drayer of 710 ESPN Seattle reports.
The transaction opens up a spot on the 40-man roster for reliever Keynan Middleton, whom the Mariners signed to a one-year deal in a corresponding move. After being scooped up off waivers from the Reds in September, Ervin struggled at the dish during his one-month stint in Seattle, slashing .205/.340/.282 with three doubles and no home runs.