SCREWSLUICE

talked a buddy into buying a big lake fishing boat one month ago. We're both new to the sport but learning fast. I play first mate/mechanic/roustabout. We have GPS and 2 sonar units. 15yr old electronics or so. We constantly "mark" fish at various depths. It seems like too many echos to all be fish. Could it all be fish or is this a set up/adjustment issue or should we consider upgrading the units? Not catchin much yet