Sockeye do bite in freshwater. The first time I intentionally targeted sockeye was before there was rentention by sporties allowed on the Fraser. Having never heard of flossing at this point I used a three foot leader and caught one fish after another. I continue to use a three or four foot leader and continue to catch fish consistently. I've caught sockeye on both fly (using a short tippet) and using marabou jigs on other systems. Of course my buddies say that the only reason I fish with short leaders is that I'm too cheap to tie longer ones.