I believe the chart can be found here, which is linked from the old attheoak.net site which is now http://www.wtv-zone.com/riparian/index.html:
http://www.wtv-zone.com/riparian/taylor/lat-depths.html
I've tried to cut and paste below.
North Lat Line Approximate Depth Of Water 23N 50' 24N 100' 25N 250' 26N 300' 27N 400' 28N 450' 29N 500' 30N 550' 31N 575' 32N 600' 33N 610' 34N 605' 35N 600' 36N 590' 37N 560'
If you continue trolling north after this and the numbers keep dropping, it means perhaps you should do a 180, unless you have a Canadian license.