"The Day I Learned to Always Wear a Hood" was also because of perch ... around here they can be anywhere from a few inches to 12"+. One fine summers day my dive buddy suggested "Hey, it's so warm, we should dive without our hoods!" which seemed like such a great idea at the time. And then we passed below the thermocline, and I had the mother of all ice cream headaches. The cold was so bad it kind've put me into a stupor while my brain was trying to figure out how to process the extreme sensory input. That was when the perch struck. You know how when you hook a fish with a rod and reel, and he jigs about on the hook while you try to reel him in? That's what this little bugger was doing on my ear.
So most people wear hoods all the time here. All this means is that now when I get perch bites they are usually on my lips. Nice. I seem to get them a lot and so I have gotten a reputation as the "guy who gets bit by perch". I often feel them biting my suit, hoses and fins too.