These tags have been implanted in steelhead smolts for more than a decade. Plus a wide variety of other salmonids and fish.

There is no way that I know of to assess the impact of the tags because you can't monitor the non-tagged fish in the same way. At least some of the fish have been recovered as adults with the tag still in.

Lots of searun cutthroat and anadromous native char have been tagged and monitored through the sound.

One of the first surprises I saw with the results was the loss of migrants all over the place, for all species. The rate of loss, per km migrated, was highest for the shortest migration. That is, early in the migration they get hammered.

Long time ago, we clipped coho, steelhead, and rainbow as they left a small lake on their way to sea. Then, recaptured them 5km downstream. Lost about 10% or more in that short trip.