Buck,

I don't have any stats on how much weight they lose, but I can tell you that a very thin steelhead will weigh about 30% less than an average girth steelhead of the same length. Likewise, a really fat or big-shouldered steelhead will weigh about 30% more than an average steelhead of the same length. This is real helpful in estimating the weight of a steelhead you want to release if you know how much an average steelhead of that length would weigh. Ex. a 32 inch "average" steelhead weighs about 10 pounds. A spawned out 32 inch steelie would weigh 20 to 30% less (7 to 8 pounds). A girthy 32 inch steelie will weigh 12 or 13 pounds.