My thoughts on this is that they do scare off other fish to a degree. Last year I was fishing a little bit below Ky Lake dam and was catching smallmouth Bass in the 12"-14" range and had one on my line swimming in a circle when my pole bent over double and a big Gar swam by with my 14" SM cross ways in it's mouth and broke my line. I wouldn't have thought it could even swallow the fish but it did attack it. When I've seen heavy Gar present the bite for other fish always seems off for me.