Mergansers can do a hurtin' on fish pops in rivers & streams as they hunt in packs. I've seen them on some very small trout streams. I once spooked a bunch and one of them actually regurgitated its last few meals when it saw me (this happens to me on some blind dates too. lol) any how the pic is below. It was two white suckers and a 4" wild brown. This is one mergansers meals in one hour or less of feeding. Multiple this by thousands of birds times hundreds of days of feeding and u can see how they could put a serious dent in fish pops. IDC about the suckers but the trout? That's another issue entirely. I've also seen them on the Raritan(main & both branches), Delaware and Paulinskill.
I've seen cormorants at Merrill staring down at me from the standing timber but never seen them feeding. That reservoir is chock full of fish so they don't seem to be bothering the fish there.
