Whalen (shoulder) was activated from the disabled list and optioned to Triple-A Tacoma, Ryan Divish of the Seattle Times reports.
Whalen opened the season on the DL after experiencing some inflammation in his throwing shoulder, something the Mariners wanted to be cautious with after his 2016 was cut short due to a shoulder issue. He'll head straight to Tacoma where he'll likely slot into the starting rotation there, but he could eventually earn a call-up with the Mariners if an opportunity arises.