G-man
You need to remember that they are a fall spawner so many of the fish caugth in winter , especially those over 16 inches are kelts (spawn-outs). The first fish to come downstream from the spawn often take advantage of the spawning salmon's eggs (mostly chums) and get into condition pretty quick. Those that drop downstream latter (February and March) don't have as much food as those earlier fish so tend to be skinny.

Those June fish had a chance to recover from the spawning. The other thing is those June fish had a chance to recover from the winter's fishing pressure and those are easier to catch. While the common wisdom is "Dollies" are easy to catch may experience has proven to be exactly the opposite. With fishing pressure they become much harder to catch, especially the larger fish.

In the Skagit the anadromous fish are usually 2 year smolts, sometimes 3 year fish. Most fish spawn the first time at age 4 or 5. A 6 pound fish might be as old as 6 to 10 years old. Some fish may live as long as 15 or more years.

Tight lines
Smalma