Now we are talking...
Bulls can be caught in the lake; I'm not sure on the impact from the river water. For fishing tips on how to catch sharks I'd suggest you try
This site focus on land based shark fishing and you can learn more then you ever imagined and make some great friends as well.
From Technique to leaders to places and people.
If interested we frequently travel to grand isle to fish for sharks, you would be more then welcome to join us, we will show you everything we know.
As for bait Mullet can get caught with a cast net in the lake, could also land you some black drum or big reds. Sting Ray is shark great shark bait and probably one of the most common used by LBSF. Always try to use the freshest bait you can get. I'm assuming that you are catching and releasing your sharks and you mentioned that you were using circles, should be at least a 16/0 circle, we use 20/0's on the island. All depends on the size of Shark you want to catch and bait size. We use baits as small as a 1/2 of a Mullet up to a 50lb whole stingray/Jack/king fish etc...
For fishing in the lake I’d assume that your targeting around 5ft Bulls. We use would use about a 5ft bite section of at least 400lb steel braid 10-15ft 400lb monofilament leader (or Weed eater line). Sharks sometime spin and get coiled in your line; this is only one reason why you will want a long leader. Another is it make it a lot easier to drag them out the water unless you have a tail rope.
Would probably not be using a cork unless you are trying to keep the bait off the bottom or you were in 100 ft of water. Typically we drop our baits in water 8 to 25 ft deep on the bottom with a 3-8oz weight depending on the current and surf conditions.
Try out the web site, we are actually having a meet in Texas next weekend with all land based shark fisherman. We will also be in Grand Isle this weekend. Shoot me an e-mail and we can discuss shark fishing so we don’t bore the others on this site.