Hi, welcome to science buddies!
Since both of the projects you picked are abbreviated, there's a lot of room for modification and creativity when planning your course of action. It would be very helpful if you could think of a hypothesis that sounds interesting to you in regards to either of these topics.
For example, if you choose to work on the topic of sand beaches, you can formulate a hypothesis about how man-made sand beaches affect the balance of life in the intertidal zone for creatures that are accustomed to living by a rocky beach. There are several ways to test this, one of them being making a model water table, as suggested in the project brief.
If you choose to work on sustainable fishing, you could easily survey local grocery stores and note which types of fish they offer and cross-check your list with the information supplied on this website:
http://www.montereybayaquarium.org/cr/S ... sheet.aspx
The page suggests you do molecular studies on the fish to confirm their identity, but if that is unavailable to you, you can always identify them yourself. While it's easy to look at a fish and assume it is like any other, it is really not difficult to discern between them if you are familiar with the types. When in doubt, use a dichotomous key!
If you need any more help, let me know.