i usually fish the same 10 square miles all year but I agree terrafin is essential. Yes to know where to fish but absolutely to see where NOT to fish. I occasionally will be at loudoun if I have to. I'm not fishing temp breaks but more fishing structure with good water conditions and if you have high chloro levels the fishing can be tough. I used to fish without the charts ( not knowing any better ) for years and had many days of fishing in bad water. Cold water plankton blooms can plague a guy out there.Aren't the tuna in the same general area (when they do show up)? What I mean is, aren't you fishing the same basic locations i.e. 5-6 sq. miles for the most part of each canyon, and only really venturing to 60 miles looking for them off Tofino early on in the season? Is Terrafin therefore really useful to a tuna fisherman that isn't one of the first out there? Are you using Terrafin in the last week of August or during the shootout?
It's nearly essential. The fish school at the temp and color breaks. Without knowing where those breaks are you and just trolling around blind.