PFunk -
Actually there are several cases of "trout" being in west side rivers. There are sea-run cutthroat in most streams (in north Puget Sound lots of them), in the upper reaches there seems to be overlaps between steelhead and resident rainbows, and there are the Dolly Varden/bull trout. In addition there are a number streams with beaver ponds with resident trout that are included in the westside regs as streams.

Technically the folks fishing during the summer are not catching smolts - steelhead, cutthroat or char - but rather parr (next year's smolts). As pointed out by Obsessed the smolts are 6 to 8 inches long with a peak outmigration occurring in May - the vast majority are out of the stream by the first of June - thus the June 1 opening.

The minimum size limit of 14 inches was designed to protect the various parr and to protect cutthroat and resident rainbows until the majority have had a chance to spawn.

If there is concern is about protecting the parr than in addition to season and size restriction that were suggested by Obsessed the prohibition of the use of bait would be helpful. The reason bait bans are nor more commonly seen is due to the active opposition to such rules by steelhead/salmon anglers.

Tight lines
Smalma