Cougars is too generic.
Eagles is taken (Philadelphia).
Emeralds is lame.
Evergreen is a plant.
Firebirds is meh, Thunderbirds would be perfect, but a Vancouver university hockey team uses it.
Kraken is cheesy.
Rainers is too specific.
Renegades is very un-Seattle.
Sea Lions is kind of cool, but too similar to Seahawks.
Seals has been done.
Sockeyes is pretty cool, very unique, has original colour options.
Totems is sacred object for First Nations so I don't think it's appropriate.
Whales just doesn't feel right.