Salmo,

They have actually found that, since the listing in 1999, the two populations are likely more associated with migration timing than fork-specific distributions, in general. These are a summer and a more fall-timed component. The summers are more prevalent spawning in the NF and the "falls" more in the SF, but they both overlap in space a bit. The captive brood program is on the fall or "SF" population and yes, they can tell the pops apart genetically.