I've been on a few sturgeon and ocean charters. Generally for a group of 4-5 we'll throw in an extra $100 or so depending on how hard we feel the guide worked. This may be a little on the cheap side but the guide always seemed appreciative.
I do agree with Gone_Fishing_ that it is a bit bizzare how some people we are expected to tip and others not. I hate tipping but generally I tip the expected rate in restaurants and so on as I can afford to and dont want to look like a cheap bugger and embarass my wife.
The family owned business that services our vehicles is fantastic and has done a fair bit of work here and there without charging us extra. Never tipped them. Same with the place we buy our tires. Also remember when I was a young lad I worked a lot on min wage jobs (flippin burgers) and never got a single tip. Also lived in Japan for 4 years in my 20s and liked that you never tipped anyone! Anyway, it is what it is and if you hope to ever use the same company/guide again you had best leave an adequet tip assuming your experience is positive.