August is the height of the spot prawn season; the deep water version of these "lobsterettes." While some believe the term "shrimp" refers to the salt water crustacean, while "prawn" covers the fresh water version, in truth, prawns migrate, like salmon, from salt water to fresh water. Technically prawns are a different species than shrimp (with narrower bodies and longer legs), but the term is used loosely to describe any large shrimp as well.
June - December
They should smell of the sea, not ammonia. Cooked, shelled shrimp look plump and succulent.
Rinse and store fresh shrimp on ice, but not in it. The water will rinse away their flavor, so give them drainage. They will keep for 2 days in the fridge this way and a day more if cooked. Frozen they will last up to 3 months.
Cooking in the shells will impart more flavor, but whether to devein is a matter of personal preference only. There can be some grit in the largest shrimp or prawns, but usually it is completely unnecessary, except for cosmetic purposes.