ReelSmoker- both fish are in the same scientific "family" so I guess you could say they are brothers who choose different lifestyles. That said there are cutties that live like steellehad, steelhead that live like cutties, and resident river varieties of both. sometimes they even sleep together (gasp). size of all salmonids seems to be directly related to amount of time they spend in the salt feeding. Coho salmon and steelhead also have a very similar life history.