rickie and wilbur,

yes, those dark lines or shadows you referred to are the weak returns from behind the dock support pilings on that particular setting.

In the darker pictures, (post #3) those bright spots are the support pilings as well, same dock but on 800khz instead of 455hkz. guess it all depends on what you're preference is in viewing. I am assuming that fish would show up as bright spots as well if there were any fish holding under the dock on the 800hkz setting , and there would be some shadows on the 455hkz setting.

If you look closely at the shadows or bright spots, they run in straight lines (for the most part and depending on the approach angle of the SI beams/boat position).