This is the most time consuming achievement of the game. You will need to complete 6 seasons (3 king crab and 3 opilio = 6 seasons). Your best bet is to take a simple boat on the the first 2 seasons and just fish for money (you do not need to be first in any season, you only need to catch $1,500,000 worth of crab in the last season) so you can buy an expensive boat starting in season 3 or 4. Upgrade the boat to a nice 150+ pots capacity for seasons 5 & 6. During the 6th season my suggestion is to find 2 good spots somewhat close to the top of the screen and near one of the docks and just drop 50 pots in each one. Make sure and see if other boats are in your area. If they are, move to another spot since they will basically turn your crab collection into about 1/3 of what it would normally be based on the yellow bar for crab amount in the area.
Get a good crew as well. I had two 3% share schmucks who I alternated the dropping of pots between and then picked a single person for retreiving pots, sorting crab & unloading and only used that particular person on each job. I used Katie & Jonathan for dropping, Neal for retrieving, Lenny for sorting & Freddy for unloading.
Make sure to keep them all rested as much as you can. The more rested they are the longer your bonus bars last, giving you an opportunity for pulling in maybe $200,000-$400,000 extra in a single season that is added to your crab catch totals. When you get close to the end of season 6 you should have well over $1.5 million. I ended up with slightly over $2 million caught at the end of season 6.