LT,

Generally, fin clipping is done from the fall through February, with smolt releases beginning around mid-April. The fin clipping is done when water temperatures are cool and the juvenile fish don't have loose scales. Loose scales are associated with smoltification. So there is a good amount of time for the marking scar to heal before the fish smolts and begins its seaward migration.

Mortality associated with fin clipping and coded-wire-tagging is typically less than 1%. Fin clipping and tagging juveniles while they are smolts is higher, depending on species, water temperature, and handling. It could be as little as 1 or 2% with coho and as high as 10 or 20% with sockeye or spring chinook smolts. You can see why it's generally preferable to avoid marking and tagging smolts, but sometimes that's the only way to obtain a mark group of wild fish.

Sincerely,

Salmo g.