From September to December weather permitting, trout fishermen often find themselves alone on the many lakes and streams that contain trout. The 2 1/2 million visitors who roam Yosemite National Park each season have left, while hungry native rainbows prowl the shallow streams in search of perfectly presented flies and salmon eggs. The pursuit of trout is the best excuse to grab a front-row seat and watch Mother Nature gently cover her Yosemite in quiet winter robes. The rainbow is the only true native trout in the park. Its particular twist of DNA can be traced to the Merced and the Tuolumne rivers. The Pleistocene Glaciers destroyed the ancient trout habitat, and fish no longer could climb back upstream and spawn.