Re: Depth sounder limits?
Actually, in this case, the Gulf Stream is loosely defined as "the edge", which is where the shelf starts to drop off rapidly at about the 100' line. On most days, you can figure this out without even having a sounder; there will be a line of boats. If you really want to know when you are inside what is officially the Gulf Stream, all you need is to watch your thermometer; the temperature climbs precipitously. But you don't really need to go out into the stream proper to catch a lot of fish, and it really depends on what type of fish you are talking about. Many fish are found in much shallower water, including cobia, snapper, grouper, tarpon, etc. Getting out to "the edge" adds other types of (generally larger) fish, such as dolphin, wahoo, sailfish, or marlin.
I know this doesn't address the question about how deep a recreational sounder can go (in my experience, less than 500-600 feet), but it seems this is what you are really asking about. Pete