I found a post that may help (from another website): "So ever since I got my fishing rod I've obviously been targeting sharks due to their value.
Aside from their price, they are very good because you know their value before catching them. No going after mystery fish and ending up with a bunch of sea bass. So if you could only catch sharks you could fill your inventory up with high value fish, making each trip to the store worth 125-150k.
The problem of course is that sharks aren't very common and it would take a long time to fill your inventory with sharks if you only cast when one was available.
Well, it doesn't have to be slow to harvest sharks.
Here's the trick: When you "Save and Continue", the fish in the ocean are reset. This means that each time you save there is approximately a 30-50% chance that you will have at least one shark spawn. It only takes about 10 seconds to save. So, to harvest sharks, go to your longest beach. A vertical beach is better because you can run up it to save time and still be able to stop in time to not scare away sharks because you can see their fin on the horizon. Save at one end of your beach and then run across it to the other end. Catch all the sharks you see(if any) then save at the other end and run back. Repeat until your inventory is full of sharks and then go sell it for a 6-figure payday.
Some might consider this an exploit so it might not be for everyone, but if you don't mind it then, enjoy.
Thanks for reading. As a note I have only tested this on my game but it seems to be working reliably. If this has already been posted, then sorry but I never saw it when I searched."
Link to the post:
http://www.gamefaqs.com/boards/997811-animal-crossing-new-leaf/66413909
